New Simplified Chemistry Class 10 ICSE Solutions – Acids, Bases and Salts

New Simplified Chemistry Class 10 ICSE Solutions -A: Acids, Bases and Salts

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QUESTIONS

2004

Question 1.
Which of the methods, A, B, C, D or E is generally used for preparing the chlorides listed below from (i) to (v)

(A) Action of an acid on a metal
(B) Action of an acid on an oxide or carbonate
(C) Direct combination
(D) Neutralization of an alkali by an acid
(E) Precipitation (double decomposition)

  1. Copper (II) chloride
  2. Iron (II) chloride
  3. Iron (III) chloride
  4. Lead (II) chloride
  5. Sodium chloride Each method is to be used only once.

Answer:
(1) B (2) A (3) C (4) E (5) D

2005

Question 1.

Match from A to F:
A: Acidic oxide,
B: Alkali,
C: Amphoteric oxide,
D: Basic oxide,
E: Deliquescence,
F: Efflorescence

  1. The property of spontaneously giving up water of crystallization to the atmosphere.
  2. A compound, soluble in water and the only negative ions in the soln. are hydroxide ions

Answer:

  1. F: Efflorescence
  2. B: Alkali

Question 2.

What is observed when, neutral litmus soln. is added to sodium hydrogen carbonate solution.
Answer:
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 1

Question 3.

The preparation of lead sulphate from lead carbonate is a two-step process.                                            (Lead sulphate cannot be prepared by adding dilute sulphuric from lead carbonate.)

  1. What is the first step that is required to prepare lead sulphate from lead carbonate.)
    Ans. Treatment with dil. nitric acid to form soluble lead nitrate.
  2. Write the equation for the reaction that will take place when this first step is carried out.
    Ans. PbCO3 + 2HNO3Pb(NO3)2 + H20 + CO2
    Insoluble
  3. Why is the direct addition of dil. H2SO4 to PbCO3 an impractical method of preparing lead sulphate.
    Ans. Direct addition of dil. sulphuric acid to lead carbonate will lead to deposition of lead sulphate on the surface of lead carbonate which stops further reaction of sulphuric acid on it.

Question 4.

Fill in the blanks:
An acid is a compound which when dissolved in water forms hydronium ions as the only
(1) ….  ions. A base is a compound which if soluble in water contains (2)…. ions. A base reacts with an acid to form a (3)…… and water only. This type of reaction is known as (4)…….
Answer:

  1. Positive
  2. Hydroxyl
  3. Salt
  4. neutralization.

Question 5.

Acid dissolve in water to produce positively charged ions. Draw the structure of these ions
Answer:
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 2

Question 6.

Name the ion other than ammonium ion formed when ammonia dissolves in water. Give one test that can be used to detect the presence of the ion product.
Answer:
Hydroxide ion.

2006

Question 1.

Mention the colour changes observed when the following indicators are added to acids:

  1. Alkaline phenolphthalein solution.
    Ans. Pink solution becomes colourless
  2. Methyl orange solution
    Ans. Orange solution changes to red or pink
  3. Neutral litmus solution
    Ans. It turns red

Question 2.

Which of the following hydroxides is not an alkali – (Choose from the choices A, B, C and D)
(A) ammonium hydroxide
(B) calcium hydroxide
(C) copper hydroxide  
(D) sodium hydroxide

2007

Question 1.

Complete the blanks from the list given:

Ammonia, Ammonium, Carbonate, Carbon dioxide, Hydrogen, Hydronium, Hydroxide, Precipitate, Salt, Water. A solution X turns blue litmus red, so it must contain (1) …. ions ; another solution Y turns red litmus blue and therefore, must contain (2)……. ions. When solutions X and Y are mixed together the products will be a (3) …. and (4) If a piece of magnesium were put into solution X, (5)….. gas would be evolved.
Answer:

  1. hydronium
  2. hydroxide
  3. salt
  4. water
  5. hydrogen

Question 2.

Match the following:
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 3

New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 4
Answer:
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 5

Question 3.

Write balanced equation for formation of PbCl2 from Pb(NO3)2 soln. and NaCl soln.
Answer:
Pb(NO3)2 + 2NaCl → PbCl2 + 2NaNO3

2008 

Question 1.

What is the term defined i) A base which is soluble in water.
Answer:
Alkali.

2009

Question 1.

The acid which contains four hydrogen atoms –
(1) Formic acid
(2) Sulphuric acid
(3) Nitric acid
(4) Acetic acid

Question 2.

A black coloured solid which on reaction with dilute sulphuric acid forms a blue coloured solution is:
(A) Carbon
(B) Managanese (IV) oxide
(C) Lead (II) oxide
(D) Copper (II) oxide

Question 3.

Solution A is a strong acid
Solution B is a weak acid
Solution C is a strong alkali

Question 3(1).

Which solution contains solute molecules in addition to water molecules ?
Answer:
Solution B — weak acid

Question 3(2).

Which solution will give a gelatinous white precipitate with zinc sulphate solution? The precipitate disappears when an excess of the solution is added.
Answer:
Solution C — strong alkali

Question 3(3).

Which solution could be a solution of glacial acetic acid ?
Answer:
Solution B — weak acid

Question 3(4).

Give an example of a solution which is a weak alkali.
Answer:
Ammonium hydroxide — weak alkali

Question 4.

Write the equation(s) for the reaction(s) to prepare lead sulphate from lead carbonate.
Answer:
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 6

Question 5.

Define the following terms : Neutralization
Answer:
Neutralisation: The reaction in which an acid reacts with a base to form salt and water is known as neutralisation.
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 7

2010

Question 1.

A: Nitroso Iron (II) sulphate
B: Iron (III) chloride
C: Chromium sulphate
D: Lead (II) chloride
E: Sodium chloride.
Select from A, B, C, D and E –

  1. A compound soluble in hot water but insoluble in cold water.
  2. A compound which in the aqueous solution state,is neutral in nature.
  3. A deliquescent compound.

Answer:

  1. Lead (II) chloride
  2. Sodium chloride
  3. Iron (II) chloride

Question 2.

Select the correct answer from A, B, C and D –

(1) A weak organic acid is:
A: Formic acid  
B: Sulphuric acid
C: Nitric acid
D: Hydrochloric acid

(2) A complex salt is:
A : Zinc sulphate
B : Sodium hydrogen sulphate
C : Iron (II) ammonium sulphate
D : Tetrammine copper (II) sulphate

Question 3.

Give an equation for the conversions

  1. ZnSO4 to ZnCO3
  2. ZnCO3 to Zn(NO3)2

Answer:
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 8

Question 4.

A: NaOH sol. : B: weak acid C: Dil. H2SO4
Select the one which contains solute ions and molecules.
Answer:

  1. Solution C
  2. Solution A
  3. Solution B

Question 5.

Give balanced equation/s for the preparation of the following salts:

  1. Copper (II) sulphate from CuO.
  2. Iron (III) chloride from Fe.
  3. K2SO4 from KOH sol.
  4. Lead (II) chloride from PbCO3 (give two equations)

Answer:
(1)
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 9

(2)
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 10

(3)
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 11

(4)
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 12

2011

Question 1.

Write the balanced chemical equation: Lead nitrate solution is added to sodium chloride solution
Answer:
Pb (NO3)2 + 2NaCl → PbCl2 + 2NaNO3

Question 2.

Name the method used from the list:
A: Simple displacement
B: Neutralization
C: Decomposition by acid
D: Double decomposition
E: Direct synthesis

For preparation of the following salts –

  1. Sodium nitrate
  2. Iron (III) chloride
  3. Lead chloride
  4. Zinc sulphate
  5. Sodium hydrogen sulphate.

Answer:
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 13

2012

Question 1.

Match the following:
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 14
Answer:
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 15

2013

Question 1.

Select the words given below which are required to correctly complete the blanks –
[ammonia, ammonium, carbonate, carbon dioxide, hydrogen, hydronium, hydroxide, precipitate, salt water]:

  1. A solultion M turns blue litmus red, so it must contain
    (1)………..ions ; another solution O turns red litmus blue and hence, must contain, (2)……… ions.
  2. When solution M and O are mixed together, the prod­ucts will be (3)………. and (4) ……………..
  3. If a piece of magnesium was put into a solution M,(5)……………..gas would be evolved.

Answer:
(1) hydronium (2) hydroxide (3) salt (4) water (5) hydrogen.

Question 2.

Give a suitable chemical term for:

  1. A salt formed by incomplete neutralisation of an acid by a base.
  2. A definite number of water molecules bound to some salts.

Answer:

  1. Acid salt
  2. Water of crystallisation

Question 3.

Choosing the substances from the list given:
dil. Sulphuric acid, Copper, Iron, Sodium, Copper (II) carbonate, Sodium carbonate, Sodium chloride, Zinc nitrate
Write balanced equations for the reactions which would be used in the laboratory to obtain the following salts:

  1. Sodium sulphate
  2. Zinc carbonate
  3. Copper (II) sulphate
  4. Iron (II) sulphate.

Answer:

  1. Sodium sulphate
    Na2CO3 + H2SO→ Na2SO4 + HzO + CO2

  2. Zinc carbonate
    Zn(NO3)2 + Na2CO3→ ZnCO3 + 2NaNO3
  3. Copper (II) sulphate
    CuCO3 + H2SO→ CuSO4 + h2o + CO2
  4. Iron (II) sulphate.
    Fe + H2SO→ FeSO4 + H2

Question 4.

Identify: An acid which is present in vinegar.
Answer:
Acetic acid or ethanoic acid.

2014

Fill in the blank from the choices given:

Question 1.

The basicity of Acetic Acid is 1.

Question 2.

Draw the structure of the stable positive ion formed when an acid dissolves in water.
Answer:
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 16

Question 3.

State the inference drawn from the following observations:
Salt S is prepared by reacting dilute sulphuric acid with copper oxide. Identify S.
Answer:
The compound or salt S is copper sulphate CuSO4
CuO + H2 SO4  → CuSO4 + FlO

Question 4.

Give balanced chemical equations to prepareation of the following salts:

  1. Lead sulphate-from lead carbonate.
  2. Sodium sulphate-using dilute sulphuric acid.
  3. Copper chloride-using copper carbonate.

Answer:

(1) Lead sulphate from lead carbonate.

PbCO3 + HNO3 → Pb(NO3)2 + H2O  + CO2
Pb(NO3)2 + H2SO4  → PbSO4 + 2HNO3

(2) Sodium sulphate using dilute sulphuric acid.

Na2CO3  + H2SO4(dil) → Na2SO4  +  H2O+ CO2

(3) Copper chloride using copper carbonate.

CuCO3  +   HCl(dil) → CuCl2   +   H2O  + CO2
(Insoluble)

2015

Question 1.

Give balanced chemical equations for the following conversions.Fe→ Fed,
Fe →FeCl3
Answer:
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 17
Question 2.

From the list of salts — AgCl, MgCl2, NaHSO4, PbCO3, ZnCO3, KNO3, Ca(NO3)2 Choose the salt that most appropriately fits the descrip­tion given below:

  1. A deliquescent salt.
  2. An insoluble chloride.

Answer:

  1. A deliquescent salt = MgCl2
  2. An insoluble chloride=AgCl

Question 3.

From the following list of oxides — SO2, SiO2, Al2O3, MgO, CO, Na2O -Select an oxide which dissolves in water forming an acid.
Answer:
SO2

2016

Fill in the blank:

Question 1.

Higher the pH value of a solution, the more………… (acidic / alkaline) it is.
Answer:
Higher the pH value of a solution, the more alkaline it is.

Question 2.

Match the following salts given below:

(1) Pb(NO3)2 from PbO
(2) MgCl2 from Mg
(3) FeCl3 from Fe
(4) NaNO3 from NaOH
(5) ZnCO3 from ZnSO4
With their correct method of preparation from: A, B, C, D and E.
(A) Simple displacement
(B) Titration
(C) Neutralization
(D) Precipitation
(E) Combination
Answer:
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 18

2017

1. Fill in the blanks from the choices given in brackets –

Question 1.

When a metallic oxide is dissolved in water, the solution formed has a high concentration of________ ions. [H+,H3O+, OH ]
Answer:
When a metallic oxide is dissolved in water, the solution formed has a high concentration of OH” ions.

Question 2.

.Choose the correct answer from the options –
(1) to increase the pH value of a neutral solution, we should add: A. An acid; B. An acid salt; C. An alkali; D. A salt,
(2) Anhydrous iron [in] chloride is prepared by:
(A) direct combination;
(B) Simple displacement;
(C) Decomposition;
(D) Neutralization.
Answer:
C. an alkali

Question 3.

Write a balanced chemical equation for the preparation of each of the following salts:

  1. Copper carbonate,
  2. Ammonium sulphate crystals.

Answer:
CuSO4(aq) + Na2CO3(uq) → Na2SO4(aq) + CuCO3(s)
2NH4OH(aq) + H2SO4(aq) → (NH4)2SO4 + 2H2O

Additional Questions

Question 1.

Define the following as per ionic theory with examples and ionic equations wherever relevant
(1) acid
(2) base
(3) alkali
(4) neutralization
Answer:
(1) Acid — An acid is a compound which when dissolved in water yields – hydronium ions (H3O+ ) as the only positively charged ion.
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 19

(2) Base — A base is a compound which reacts with hydronium ions of an acid – to give salt and water

CuO + 2HCl → CuCl2 + H2O

(3) Alkali — An alkali is a compound which when dissolved in water yields Hydroxyl ions (OH) as they are negatively charged ions.
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 20
Alkali is a base soluble in water.

(4) Neutralization — | H+ions of an acid completely or combine with |OH+| ions of a base to give salt and water only.

Acid + Base → Salt + Water
HCl + NaOH → NaCl + H2O

Question 2.

Differentiate between:

  1. Organic and inorganic acids
  2. Hydracids and oxyacids with examples.

Answer:
(1)
Organic acids – Those acids which are derived from plants, e.g., citric acid, acetic acid, tartaric acid Inorganic acids – Acids derived from minerals e.g. HCl2,h2SO4
(2)
Hydracids – Acids containing hydrogen and a non-metallic element other than oxygen, e.g. HCl, HBr, HI.
Oxyacids – Acids containing hydrogen, another element and oxygen, e.g. HNO3, H,SO4.

Question 3.

State on what basis does the strength of an acid and an alkali depend on.
Answer:
Strength of acids depends upon concentration of hydronium ion |H3O+| present in an aqueous solution
of an acid. Strength of alkali depends on the concentration of the hydroxyl ions |OH| present in an aqueous solution of an alkali.

Question 4.

Differentiate between (1) strong and weak acid (2) strong and weak alkali with suitable examples and ionic equations.
Answer:
(1) Strong Acid – Is an acid which dissociates – almost completely in aqueous solution there by producing a – high concentration of hydrogen [H+] ions [or H3O+ions]
Examples: Hydrochloric, Sulphuric and Nitric acid.

New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 21
Weak Acid – Is an acid which dissociates – only partially in a aqueous solution thereby producing a – low concentration of hydrogen [H+] ions [or H3O+ ions].
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 22

(2) Strong Alkali – Is an alkali which dissociates – almost completely in aqueous solution thereby producing a – high concentration of hydroxyl [OH] ions.
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 23

Examples: Lithium, Sodium and Potassium hydroxide
Weak alkali – Is an alkali which dissociates – only partially in aqueous solution thereby producing a – low concentration of hydroxyl [OH ] ions.
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 24
Examples: Ammonium hydroxide and Calcium hydroxide.

Question 5.

Name the ions formed when – HCl ; HNO3 ; H2SO4 ; CH3COOH ; NaOH and NH4OH ionise in aq. soln.
Answer:
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 25

Question 6.

State giving reasons which is a stronger acid – dil. HCl or cone. H2CO3.
Answer:
Dil. HCl is a stronger acid than cone. H2CO3
Reason: HCl ionises almost completely in aqueous solution thereby producing a high concentration of Hp ions in aqueous solution. On the other hand, H2CO3 ionises to a very small extent producing a low
concentration of HO+ ions. More the concentration of H3O+ ions in solution, stronger is the acid. Hence dil. HCl is a stronger acid than cone. H2CO3.

Question 7.

State why the basicity of acetic acid is one and acidity of calcium hydroxide is two.
Answer:
Basicity of an acid is the number of hydrogen ions which can be produced from one molecule of the acids on complete dissociation. Acetic acid, CH.COOH gives one H+ per molecule the acid, hence acetic acid is monobasic i.e., its basicity is one.
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 26
Acidity of a base is the number of hydroxyl ions which can be produced from one molecule of the base on complete dissocation. Ca(OH)2 (calcium hydroxide) gives two hydroxyl ions per molecule of the base, hence calcium hydroxide is diacidic i.e., its acidity is two.

Question 8.

Give three reasons with equations wherever required, why sulphuric acid is a dibasic acid.
Answer:
Sulphuric acid (H2SO4) is a dibasic acid as explained below:

(1)
It ionises in aqueous solution to produce two hydrogen ions per molecule of the acid.

OR

It contains two replace all hydrogen ions per molecule of the acid.
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 27

(2)
It ionises in two steps in aqueous solution as shown below:
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 28

(3)
It forms two types of salt, e., normal salt and acid salt as shown below:
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 29

Question 9.

State how acids are defined as per Arrhenius’s and Lowry – Bronsted’s theory.
Answer:
Arrhenius Theory –
Acids are substances which – dissociate in aqueous solution to give H+ ions.
Strong acids dissociate – almost completely, while weak acids dissociate partially.

Question 10.

Oxygen atom in water has two Hone pair of electrons’. Explain the meaning of the term in italics. With the help of an electron dot diagram show the formation of hydronium ion and ammonium ion from a water molecule and an ammonia molecule respectively.
Answer:
A pair of electrons not shared with any other atom for bond formation is called a lone pair of electrons. In water, the central atom – oxygen has two lone pair of electrons as shown ahead:

Structure of water molecule
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 30

Formation of hydronium ion- (H3O+): When an acid is dissolved in water the proton (H+) released by the acid add onto the lone pair electrons of the oxygen atom of a water molecule. The proton (H+) accepts the lone pair of electrons forming a coordinate bond (shown by an arrow).
HCl  → H+ + Cl
Water Proton Hydronium ion
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 31

Formation of ammonium ion (NH4+): When ammonia gas is dissolved in water, the proton released by water adds onto the lone pair of electrons of the nitrogen atom of the ammonia molecule. The proton (H+) accepts the lone pair of electrons forming a coordinate bond (shown by an arrow).
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 32
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 33

Question 11.

State how you would obtain:

  1. Sulphuric acid from an acidic oxide
  2. KOH from a basic oxide.

Answer:
(1)
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 34
(2)
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 35

Question 12.

State two chemical properties each with equations of a solution containing
(1) H+ ions
(2) OH
Answer:
(1) Properties of a solution containing H+ ions: Acids when dissolved in water produce H2O+ or H ions. Typical chemical properties of aqueous solution of acids are:

(a) Neutralisation: H+ ions react with OH ions from alkalies to give water
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 36
(b) Reaction with active metals: Active metals like Al, Zn, Fe, etc., react with dil. acids (HCl, H2SO4) to give hydrogen gas. In this reaction H+ is reduced to H, by the active metal. For example,
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 37

(2) Properties of solution containing OH ions: Alkalies when dissolved in water produce OH” ions. Typical reaction of aqueous solution of alkalies are;

(a) Neutralisation: OH+ ions react with H+ ions from acids to give water.
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 38

(b) Reaction with solutions of metallic salts: Hydroxides of metals other than Group 1 and 2 are generally insoluble in water. Such hydroxides are precipitated from their respective salt solutions by OH” ions. For example,
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 39

Question 13.

Give equations for the decomposition of a metallic
(1) chloride
(2) nitrate with cone. H2SO4.
Answer:
(1) Reaction of cone. H2SO4 with metallic chloride:
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 40
(2) Reaction of cone. H2SO4 with metallic nitrate
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 41

Question 14.

State in the above reactions a reason for the formation of the respective acids from cone. H2SO4.
Answer:
The reason for the formation of the respective acids from cone. H2SO4 is the volatility of the acid formed. At room temperature or above HCl is a gas while HNO3, which is a liquid at room temperature, volatileses at the reaction temperature (w 200°C).

Question 15.

Convert
(1) NaHCO3
(2) Na2CO3 to unstable carbonic acid by action with dil. H2SO4.
State the reason why ammonia is evolved when an ammonium salt and alkali are heated.
Answer:

  1. 2NaHCO3 + H2SO4 (dil.) → Na2SO4 + 2H2CO3
  2. Na2CO3 + H2SO4 (dil.) → Na2SO4 + H2CO3

Ammonia is evolved when an ammonium salt and alkali are heated.
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 42
This is because a non-volatile base, Ca(OH)2 displace a volatile base, NH4OH which decomposes to given NH3 and H2O.

Question 16.

Define pH value. What would you say about the pH of a solution in which (i) H+ ions = OH ions

  1. evolves CO2when heated with Na2CO3
  2. OH” ions > H+ ions.

Answer:
pH value: The pH value of a solution is defined as the negative logarithm (to the bsise 10) of the hydrogen ion concentration expressed in mol L-1. Thus,
PH = -log10 [H+]
Where [H+] stands for hydrogen ion concentration in mol L-1.

  1. A solution in which [H+] = [OH], is neutral with pH = 7.
  2. A solution which evolves CO2 with NaCO3 is acidic in nature with pH < 7.
  3. A solution in which [OH] > [H+] is basic in nature with pH >7.

Question 17.

State whether litmus is a common acid-base indictor or a universal indicator.
Answer:
Litmus is a common acid-base indicator. It is not a universal indicator.

Question 18.

State the colour change in a neutral litmus in presence of
(1) acidic
(2) alkaline medium.
Answer:
Neutral litmus is purple in colour

  1. In acidic medium colour of neutral litmus changes from purple to red.
  2. In alkaline medium colour of neutral litmus changes from purple to blue.

Question 19.

State the colour change in a universal indicator e.g. pH paper on

  1. slightly acidic soil
  2. slightly alkaline soil
  3. dairy milk
  4. human blood tested for medical diagnosis.

Answer:

  1. In slightly acidic soil colour of universal indicator changes to yellow.
  2. In slightly alkaline soil colour of universal indicator changes to blue.
  3. In dairy milk colour of universal indicator change to green.
  4. In human blood colour of universal indicator changes to green (pH = 7.3).

Question 20.

Define
(1) salt
(2) normal salt
(3) acid salt – with relevant examples and equations.
Answer:
(1) Salts: A salt is a compound formed by partial or complete replacement of the replaceable hydrogen ions of an acid by a metallic ion or ammonium ion.
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 43

(2) Normal salt: The salt formed by complete replacement of the replaceable hydrogen ions present in a molecule of the acid by metallic or ammonium ion. For example,
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 44
2NaOH(aq) + H2CO3(aq)→ Na2CO3(aq) + 2H2O (l)

NH4OH(aq) + HCl(aq)→ NH4Cl(aq) + H.O (l)

(3) Acid salt: The salt formed by partial replacement of the replaceable hydrogen ions present in a molecule of the acid by metallic or ammonium ion. For example,

NaOH(aq) + H3PO4(aq) → NaH2PO4(aq) + H2O(l)
2NaOH(aq) + H3PO4(aq)→Na2HPO4(aq) + 2H2O (l)
KOH(aq) + H2SO4(aq)→ KHS04(aq) + H2O(l)
NH4OH(aq) + H2CO3(aq)→NH4HCO3(aq) + H.O (l)

Question 21.

State:

  1. the formation
  2. the components of – a basic salt.

State which of following salts is an – acid, normal or basic salt.

  1. bleaching powder
  2. potassium mercuric iodide
  3. sodium sulphite
  4. sodium hydrogen sulphite
  5. sodium silver cyanide
  6. basic lead nitrate
  7. potassium zincate
  8. alum
  9. calcium bicarbonate
  10. basic copper chloride
  11. trisodium phosphate.

Answer:

(1) Formation of a basic salt: A basic salt is formed by partial replacement of hydroxyl group of a diacidic or triacidic base with an acid radical (or an anion other than OH).

(2) Components of a basic salt: A basic salt contains a cation (other than H+ ion), a hydroxyl ion (OH from base) and an anion (other than OH ion). For example,
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 45

  1. Bleaching powder, CaOCl, (Normal salt/Mixed salt)
  2. Potassium mercuric iodide, K2(HgI4) .
    (Normal salt/Complex salt)
  3. Sodium sulphate, Na2SO4 (Normal salt)
  4. Sodium hydrogen sulphite, NaHSO3 (Acid salt)
  5. Sodium silver cyanide, Na[Ag(CN)2]
    (Normal salt/Complex salt)
  6. Basic lead nitrate, Pb(OH)NO3 (Basic salt)
  7. Potassium zincate, K2ZnO2 (Normal salt)
  8. Alum or potash alum, K2SO4.Al2(SO4)3.24H2O
    (Normal salt/Double salt)
  9. Calcium bicarbonate, Ca(HCO3)2 (Acid salt)
  10. Basic copper chloride, Cu(OH)Cl (Basic salt)
  11. Trisodium phosphate, Na3PO4 (Normal salt)

Question 22.

Name three (1) sulphates (2) chlorides insoluble in water and – two (1) oxides (2) carbonates soluble in water.
Answer:
(1) Three sulphates insoluble in water
Lead sulphate (PbSO4), Calcium sulphate (CaSO4), and Barium sulphate (BaSO4).

(2) Three chloride insoluble in water
Silver chloride (AgCl), Lead chloride (PbCl2), and Mercury chloride (Hg2Cl2 or HgCl).

(1) Two oxides soluble in water
Sodium oxide (Na2O  ), and Potassium oxide (K2O)

(2) Two carbonates soluble in water
Sodium carbonate (Na2CO3), and Ammonium carbonate [(Na4)2CO3]

Question 23.

State the method only, generally used for the preparation of the following salts
(1) Zn(NO3)2
(2) NH4Cl
(3) ZnSO4
(4) ZnS
(5) CaCO3
(6) FeCl3
(7) PbCl2
(8) Pb(NO3)2
Answer:

Salt

Method of preparation

1.      Zn(NO3)2Neutralisation of insoluble base by acid/Decomposition of insoluble carbonate by acid
2.      NH4ClNeutralisation (titration) of soluble  base by acid/Decomposition of soluble carbonate by acid
3.      ZnSO4Neutralisation of insoluble base by acid/Decomposition of insoluble carbonate by acid
4.      ZnSDirect combination (Synthesis)/Double decomposition (Precipitation)
5.      CaCO3Double decomposition (Precipitation)
6.      Fecl3Direct combination (Synthesis)/
7.      pbCl2Double decomposition (Precipitation)
8.      Pb(NO3)2Neutralisation of insoluble base by acid/Decompostion of insoluble carbonate by acids

Question 24.

Give balanced equations for the preparation of the following salts –

(a)
(1) CuSO4  
(2) NaHSO4
(3) Na2SO4
(4) FeSO4
(5) BaSO4
(6) PbSO4 – using dil. H2SO4
(b)
(1) NaHSO4
(2) CuSO4 – using cone. H2SO4.
Answer:
(a) Using dil. H2SO4

  1. CuO (s) + H2SO4 (aq) → CuSO4 (aq) + 2H2O (l)
  2. NaOH (aq) + H2SO4 (aq) → NaHSO4 (aq) + H2O(l)
  3. 2NaOH (aq) + H2SO4 (aq)→Na2SO4 (aq) + 2H2O(l)
  4. Fe (s) + H2SO4 (aq)→ FeSO4 (aq) + H2 (g)
  5. BaCl2 (aq) + H2SO4 (aq)→ BaSO4 (s) + 2HCl (aq)
  6. Pb(NO3)2 + H2SO4 (aq)→ PbSO4 (s) + 2HNO3 (aq)

(b) Using cone. H2SO4

New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 46

Question 25.

Starting from insoluble ZnO how would you obtain insoluble ZnCO3 by precipitation.
Answer:
ZnO (s) + 2HCl (aq)→ ZnCl2 (aq) + H2O(l)
ZnCl2 (aq) + Na2CO3 (aq)→ ZnCO3 (s) + 2NaCl (aq)

Dissolve zinc oxide in minimum quantity of dil. HCl. Add to it a saturated solution ofNa2CO3 in water till
no more precipitation takes place. Filter and dry the ZnCO3 so obtained.

Question 26.

Give balanced equations for the action of a dilute acid on
(1) zinc carbonate,
(2) potassium bicarbonate for the preparation of the respective salt.
Answer:

  1. Zinc carbonate
    ZnCO3 + 2HNO3 → Zn(NO3)2 + H2O + CO

  2. Potassium bicarbonate
    2KHCO3 + H2SO4 → K2S04 + 2H2O + 2CO2

Question 27.

Give balanced equations for the decomposition of
(1) calcium bicarbonate by dil. HCl,
(2) calcium carbonate by dil. HNO3,
(3) sodium sulphite by dil. H2SO4,
(4) zinc sulphide by dil. H2SO4.

Answer:

  1. Ca(HCO3)2 + 2HCl→ CaCl2 + 2H2O+ 2CO2
  2. CaCO3 + 2HNO3 → Ca(NO.)2 + H2O+ CO2
  3. Na2SO3 + H2SO4 (dil.) → Na2SO4 + H2O+ SO2
  4. ZnS + H2SO4 →ZnSO4 + H2S

Question 28.

State what will be the effect of each of the following solution on blue litmus –
(1) K2CO3 soln
(2) KCl soln.
(3) NH4NO3
Answer:

  1. K2COis a salt of a strong base (KOH) and weak acid (H2CO3). Hence its aqueous solution will be basic in nature. It will have no effect on blue litmus solution.
  2. KCl is a salt of a strong acid (HCl) and a strong base (KOH). Hence its aqueous solution will be neutral in nature. It will have no effect on blue litmus solution.
  3. NH4NO3 is a salt of a strong acid (HNO3) and weak base (NH4OH). Hence its aqueous solution will be acidic in nature. It will turn blue litmus solution red.

Question 29.

Select the correct acid, base or salt from the list in bracket for each of the statements given below:

  1. An example of an acid derived from a mineral is……….. (citric acid / nitric acid / acetic acid)
    Ans. Nitric acid
  1. An example of a base which is not a alkali is….. (caustic soda / zinc hydroxide / liquor ammonia / caustic potash)
    Ans. Zinc hydroxide
  1. An example of a strong acid is dilute……… (acetic acid / sulphuric acid / tartaric acid / carbonic acid)
    Ans. Sulphuric acid
  1. An example of a weak alkali is…. (potassium hydroxide / calcium hydroxide / sodium hydroxide) solution.
    Ans. Calcium Hydroxide
  1. An acid having basicity 1 is……… (carbonic acid / acetic acid / sulphurous acid)
    Ans. Acetic acid
  1. An acid obtained by dissolving sulphur trioxide in water is…. (sulphurous acid / sulphuric acid oleum)
    Ans. Sulphuric acid
  1. A volatile acid obtained when nitre reacts with non­volatile concentrated sulphuric acid on heating is (hydrochloric acid / sulphuric acid/ nitric acid)
    Ans. Nitric acid
  1. A base obtained when lead nitrate undergoes thermal decomposition is……. (trilead tetroxide / lead (IV) oxide/ lead (II) oxide.                                                        .
    Ans. Lead (II) oxide
  1. An acid obtained when concentrated nitric acid is heated with sulphur is…….. (sulphurous acid / sulphuric acid / nitrous acid)
    Ans. Sulphuric acid
  1. The more volatile acid obtained when the less volatile acid reacts with sodium bicarbonate is……… (sulphuric acid / carbonic acid / nitric acid)
    Ans. Carbonic acid
  1. The insoluble base obtained when sodium hydroxide reacts with iron (III) chloride is…. (iron (II) hydroxide / iron (III) hydroxide / iron (II) oxide)
    Ans. Iron (III) hydroxide.
  1. A solution whose pH is above 7 is….. (vinegar / milk / liquor ammonia.
    Ans. Liquor Ammonia
  1. The salt formed when sulphuric acid reacts with excess caustic soda solution is…… (sodium bisulphite / sodium sulphate / sodium sulphite / sodium bisulphate).
    Ans. Sodium sulphate
  1. An example of an acid salt is……. [CH3COONa/NaNO3/ Na2HPO4/NaKCO3]
    Ans. Na2HPO4
  1. An example of a soluble salt is ……… (AgCl / PbSO4 /CaSO4 / CaCl2)
    Ans. CaCl2
  1. An example of an insoluble salt is….. (Na2CO3 \ K2CCl,/ MgCO3 / (NH4)2 CO3)
    Ans. MgCO3
  1. A salt prepared by neutralization in which titration is involved is…….. (MgCl2 / CaCl2 / NH,Cl / CuCl2)
    Ans. NH4Cl
  2. An insoluble salt prepared by direct combination or synthesis is……. [FeCl3 / FeSO4 / FeS/Fe(NO3)2] Ans. FeS
  1. A salt prepared by precipitation i.e. by double decomposition of two salt solutions is………… (Na2SO4 /PbSO4 / ZnSO4 / CuSO4)
    Ans. PbSO.
  2. A salt prepared by simple displacement i.e. action of dilute acid on a metal is____ (PbCl2/ CuCL, / AlCl3 / HgCl)
    Ans. AlCl3
  3. Decomposition of calcium hydrogen carbonate with…. [dil. HNO3 /dil. HCl/dil. H2SO4] results in formation of calcium chloride.
    Ans. dil.HCl
  1. Action of dilute acid on a metallic sulphide results in evolution of____ [SO2/H2S/CO2] gas.
    Ans. H2S
  1. A salt which on hydrolysis produces a neutral solution is……. (sodium chloride / ammonium chloride / sodium carbonate)
    Ans. Sodium chloride

Unit test Paper 3 A —Acids, Bases and Salts

l. Name the following:

  1. A basic solution which does not contain a metallic element.
    Ans. Ammonium Hydroxide.
  1. A normal salt of sodium formed from acetic acid.
    Ans. Sodium acetate, COCOON a.
  2. A base which reacts with an acid to give a salt which .on hydrolysis gives a slightly acidic solution.
    Ans. Ammonium hydroxide (NH4OH)

OR

   Calcium hydroxide [Ca(OH)2].

  1. An ion which combines with a polar covalent molecule to form an ammonium ion.
    Ans. Hydrogen ion a proton (H+).
  1. A soluble salt formed by direct combination between a light metal & a greenish yellow gas.
    Ans. AlCl3

2. Identify which of the following terms matches with the appropriate description 1 to 5.
A: Hydracid
B: Monobasic acid
C: Less volatile acid
D: Weak acid
E: Tribasic acid
F: Dibasic acid
G: More volatile acid

  1. An acid having basicity 1 and having only one replaceable hydrogen ion per molecule of the acid.
    Ans. Monobasic acid
  1. An acid which dissociates to give a low concentration of H+
    Ans. Weak acid
  1. An acid containing hydrogen and a non-metallic element other than oxygen.
    Ans. Hydracids.
  1. The type of acid which generally displaces another acid when the acid is heated with a salt.
    Ans. Less volatile acid
  1. The type of acid which reacts with a base to give an acid salt and a normal salt.
    Ans. Dibasic acid

3. State which of the following methods is generally used for preparing the salts 1 to 5 given below:

A: Neutralisation – insoluble base and dil. acid
B: Neutralisation – alkali and dil. acid
C: Simple displacement – active metal and dil. acid
D: Direct combination
E: Precipitation (double decomposition)                 .

  1. PbCO3
  2. Zn(NO3)2
  3. NaCl
  4. Cu(NO3)2
  5. FeS

Answer:

  1. PbCIO3: Precipitation (Double decomposition) (E)
  2. Zn(NO3)2: Simple displacement-active metal and dil. acid (C)
  3. NaCl: Neutralisation-alkali and dil. acid (B)
  4. (CuNO3)2: Neutralisation + insoluble base and dil. acid (A)
  5. FeS: Direct combination (D)

4. Give balanced equations for the preparation of the following salts:

  1. Calcium oxide → Calcium chloride → Calcium carbonate
    Ans. CaO + 2HCl → CaCl2 + H2O
  2. Zinc sulphide Zn→ Zinc sulphate
    Ans. Zn + S → ZnS
  3. Iron (II) chloride ← Fe→ Iron (III) chloride
    Ans. Fe + 2HCl → FeCl2 + H2
  4. Lead (II) oxide → Lead nitrate→ Lead sulphate
    Ans. PbO + 2HNO3 → Pb(NO3)2 + H2O
  5. Copper (II) oxide → Copper (II) sulphate ←Copper (II)hydroxide
    Ans. CuO + H2SC4 → CuSO4+ H2O

5. The diagram represents the preparation of sodium sulphate salt from dil. H2SO4 acid and sodium hydroxide.
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 47

  1. Name the apparatus ‘A’.
    Ans. Burette
  1. Name the substance ‘X’ placed in ‘A’ and the (substance ‘Y’ placed in B.
    Ans. Dil. H2SO4 Sodium Hydroxide
  1. State the reason for conducting the titration using the apparatus ‘A’ and ‘B’
    Ans. Titration is conducted to determine the completion of the neutralisation reaction, i.e. to determine the amount of sulphuric acid required to neutralise a known amount of sodium hydroxide.
  1. State which solution is transferred to the evaporating dish and evaporated to point of crystallisation for obtaining the salt.
    Ans. Sodium Sulphate.
  1. State why titration is not conducted for the preparation of copper (II) sulphate crystals by neutralisation.
    Ans. This is because copper (II) oxide is not soluble in water.

6. Give reasons for the following:

Question 6(1).

Concentrated sulphuric acid is a weaker acid compared to dilute sulphuric acid.
Answer:
Sulphuric acid,H2SOis a covalent compound as shown below.
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 48
When dissolved in water, polar water molecules helps in its ionisation, thus producing B,O+ ions responsible for its acidic nature. More water (i.e., dilute acid) means more H3O+ ions and hence stronger acid.

Question 6(2).

An aqueous solution of the salt ammonium chloride is acidic in nature while an aqueous solution of sodium chloride is neutral.
Answer:

New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 49
New Simplified Chemistry Class 10 ICSE Solutions Chapter 3A Acids, Bases and Salts 50

From above equation it is clear that NH4Cl forms weak alkali which is acidic in nature where as NaCl from strong alkali which is neutral.

Question 6(3).

In the preparation of an insoluble salt from another insoluble salt by precipitation [double decomposition], dilute nitric acid and not dilute sulphuric acid is generally used.
Answer:
Direct addition of dil. H2SO4 to PbCO3 is an impractical method of preparing lead sulphate since PbSO4 is insoluble and forms a coating on PbCO3, thereby the reaction slowly comes to a stop.

Question 6(4).

Acetic acid does not form an acid salt but forms a normal salt.
Answer:
Acetic acid (CH3COOH) is a monobasic acid, i.e. it contains only one replaceable hydrogen ion per molecule of the acid. As such it can only form normal salts.

Question 6(5).

Sulphurous acid forms two types of salts on reaction with an alkali.
Answer:
Sulphurous acid (H2SO3) is a dibasic acid, i.e., it contains two replaceable hydrogen ions per molecule. As such, it can form normal salt (say Na2SO3) as well as acid salt (NaHSO3) on reaction with an alkali.

 

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New Simplified Chemistry Class 7 ICSE Solutions – Elements, Compounds and Mixtures

New Simplified Chemistry Class 7 ICSE Solutions – Elements, Compounds and Mixtures

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

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Points to Remember:

  1. Every substance is made up of very tiny particles, called molecules. Molecules are formed from even smaller particles called atoms.
  2. Element—
    (a) Element is the simplest pure substance. It cannot be divided further into simpler substances by any chemical method, e.g. oxygen, hydrogen, sulphur, etc.
    (b) At present 116 elements are known, of which 92 are natural elements.
  3. Based on their properties, elements are classified into : metals, non-metals, metalloids, noble gases.
  4. Metals are ductile, malleable, good conductors of heat and electricity, high melting and boiling points. Metals are sonorous, e.g., Iron, Gold, Silver, etc.
  5. Non-metals are solids and brittle in nature, bad conductor of heat and electricity (exception Graphite) low melting and boiling points, e.g. sulphur, carbon, hydrogen, etc,
  6. Metalloids— These elements show properties of both metals and non-metals. They are hard solids, e.g. Boron, Silicon, Arsenic.
  7. Inert or noble gases— These elements do not react chemically with other elements or compounds are called noble (Inert) gases, e.g., helium, neon, argon, etc.
  8. Symbols of Elements— Each element is denoted by a symbol usually to first letter.
    Examples: Oxygen by O Hydrogen by H.
  9. Atom— “An Atom is the smallest particle of an element that can take part in a chemical reaction but may or may not have independent existence.”The atom of an element exhibits all the properties of that element.
  10. Molecule— A molecule is the smallest particle of a pure  substance of element or compound which has independent existence. It exhibits all the properties of pure substance.
  11. Atomicity— The number of atoms of an element that join together to form a molecule of that element is known as the atomicity.
  12. Molecular Formula— Molecular formula of an element is the symbolic representation of its molecule. It indicates the number of atoms present in it. e.g. Magnesium oxide- MgO.

Exercise

Question 1.
Differentiate between the terms elements, compounds and mixtures with suitable examples.
Answer:
Element — is a pure substance
e.g. Potassium

  1. It is the basic unit of matter  and cannot be broken down into two or more simpler substances by any means.
  2. It is mainly classified into metals and non-metals.

Compound — Is a pure substance
e.g. Potassium chloride

  1. It is formed by combination of two or more elements.
  2. The elements are combined together in a fixed ratio.

Mixture — is an impure substance
e.g. Potassium chloride solution

  1. It is formed by combination of two or more pure substances.
  2. The pure substances are mixed together in any ratio.

Question 2.
State which element exists in the highest percentage in – (a) earth’s crust (b) atmosphere (c) human body.
Answer:
(a) Oxygen (O) — 46.1%
(b) Nitrogen (N) — 78%
(c) Oxygen (O) — 65%

Question 3.
Elements are mainly classified into metals and non-metals. State six properties of metals which differ from non-metals.
Answer:
New Simplified Chemistry Class 7 ICSE Solutions - Elements, Compounds and Mixtures 1

Question 4.
Give the symbols of the following elements – and state in each case whether they are metals, non-metals, metalloids or noble gases.
New Simplified Chemistry Class 7 ICSE Solutions - Elements, Compounds and Mixtures 17
New Simplified Chemistry Class 7 ICSE Solutions - Elements, Compounds and Mixtures 2
Answer:
New Simplified Chemistry Class 7 ICSE Solutions - Elements, Compounds and Mixtures 3

New Simplified Chemistry Class 7 ICSE Solutions - Elements, Compounds and Mixtures 4

Question 5.
State what is meant by the term ‘activity series of metals’. State the most reactive and the least reactive metal from the following – Zn, Ag, Na, Fe, Cu, Pb.
Answer:
Activity series of metals:
The positive of metals in the decreasing order of their reactivity is called ‘activity series of metals.’
It is a series of metals arranged according to their reactivity in which the most reactive metal i.e. potassium is at the top of the series and the least reactive metal i.e. gold is at the bottom.

The most reactive metal is Na.
The less reactive metals are Zn, Fe, Pb.
The least reactive metals are Ag, Cu.

Question 6.
Give three reasons why – carbon dioxide is considered a compound, while carbon – an element.
Answer:
Carbon dioxide (C02) has a formula and properties of C02 to extinguish fire etc. are quite different from the properties it constituents carbon and oxygen. Oxygen (O) and carbon (C) are elements as these are made up of one kind of atoms. Also carbon is combustible and oxygen is supporter of combustion

Question 7.
State what information is provided by the formula of calcium hydroxide – Ca(OH)2
Answer:
New Simplified Chemistry Class 7 ICSE Solutions - Elements, Compounds and Mixtures 5

Question 8.
Four atoms of hydrogen combine with one atom of carbon to give methane [CH4]. State the valency of carbon.
Answer:
Methane is formed by the combination of four hydrogen atoms and one carbon atom where valency of hydrogen is 1 and valency of carbon is 4.

Question 9.
Write the symbols of the following elements and radicals along with their valencies.
(a) Sodium
(b) magnesium
(c) chlorine Ichioridel
(d) nitrate
(e) suiphite
(f) alurniniuni
(i) zinc
(j) sulphur [sulphide ]
(h) broniine [broiiiide]
(k) sulphate
(l) hydroxide
(m) calcium
(n) caibon.te
(o) potassium
(p) phosphate
(q) iodine[iodide]
Valency list: (i) 1+ (ii) 2, (iii) 3, (iv) 1, (y) 2-(vi) 3
Answer:
New Simplified Chemistry Class 7 ICSE Solutions - Elements, Compounds and Mixtures 6

New Simplified Chemistry Class 7 ICSE Solutions - Elements, Compounds and Mixtures 7

Question 10.
Write the chemical formula
(a) magnesium oxide
(b) Sodium bromide
(c) calcium sulphide
(d) magnesium sulphate
(e) aluminium chloride
(f) zinc oxide
(g) calcium carbonate.
Answer:

(a) MgO
(b) NaBr
(c) CaS
(d) Mg SO4
(e) AIC3
(f) ZnO
(g) CaCO3

Question 11.
Give the formulas of the following acids:
(a) hydrochloric
(b) nitric
(c) sulphuric
(d) carbonic — acid.
Answer:

(a) Hydrochloric — HCI
(b) Nitric —HNO3
(c) Sulphuric —H2SO4
(d) Carbonic acid —H2CO3

Question 12.
Give the formulas of the following gases:
(a) hydrogen chloride
(b) ammonia
(c) carbon monoxide
(d) nitric oxide
(e) nitrous oxide
(f) nitrogen dioxide
(g) nitrogen
(h) sulphur dioxide
Answer:

(a) hydrogen chloride — HCI
(b) ammonia — NH3
(c) carbon monoxide— CO
(d) nitric oxide— NO
(e) nitrous oxide — N2O
(f) nitrogen dioxide — NO2
(g) nitrogen – N2
(h) sulphur dioxide— SO2

Question 13.
Explain the term mixture. Differentiate between a homogenous and a heterogeneous mixture with one example of each in the (a) solid-solid (b) solid-liquid If (c) liquid-liquid state of the mixture.
Answer:
Mixtures:
“Are made up of two or more elements or compounds or both mechanically mixed together in any proportion.”
Examples:

  1. Iron and sand mixture.
  2. Sand, iron and common salt mixture.
  3. Ice-cream is mixture of milk, sugar absence, dry-fruits etc.
    Differences between  homogenous and heterogeneous  mixtures.

Homogenous mixture

  1. Constituents – uniformly mixed.
  2. Properties and composition same throughout the mixture.
    Example: Alloys, (salt + water),  air etc.

Heterogeneous mixture

  1. Constituents – not uniformly mixed.
  2. Properties and composition not same but varies throughout the mixture.
    Examples: (oil + water), (iron + sulphur).
    Solid – solid homogenous mixture is brass (Cu + Zn)
  3. Solid – solid heterogenous mixture is (iron + sulphur)

Question 14.
State four differences between – elements, compounds and mixtures with suitable examples.
Answer:

  1. Term —     
    Elements – Pure substance made up of one kind of atoms only. e.g. Iron [Fe], Sulphur [S]
    Compounds – Pure substance made up of two or more elements, e.g. Iron sulphide [FeS]
    Mixture – Impure substance made up of two or more elements or compounds, e.g. Iron sulphur mixture.
  2. Existence—
    Elements –
    Elements i.e. atoms of one kind are present on their own.
    e.g. Iron and sulphur exist on their own as elements iron and sulphur.
    Compounds – Components in a compound present in a definite proportion.
    e.g. Iron and sulphur are chemically combined in a fixed ratio in iron sulphide.
    Mixture – Components in a mixture present in any proportion.
    e.g. Iron and sulphur are mixed in any ratio in the mixture of iron and sulphur.
  3. Properties —
    Elements –
    Elements have a definite set of properties. Elements classified into metal and non-metals each with its own properties.
    Compounds – Compounds have a definite set of properties.
    Elements of a compound do not retain their original properties.
    Mixture – Mixture not have a definite set of properties. Components of a mixture do retain their original properties.
  4. Separation —
    Elements –
    Elements occur on their own or as compounds and can be separated by chemical and physical methods.
    Compounds – Elements in a compound are chemically combined and can be separated by chemical methods only.
    Mixture – Components in a mixture are chemically mixed and can be separated by physical methods only.
  5. Examples —
    Elements –
    Metals – Iron, copper, silver, gold.
    Non-metals – Sulphur, chlorine.
    Compounds – Iron sulphide, copper oxide, water.
    Sodium chloride, copper, sulphate.
    Mixture – Iron + sulphur, copper + silver, air, brass. Sodium chloride + water, copper sulphate + water.

Question 15.
State the correct technique for separation of the following mixtures.
(a)  a sublimable solid and a non-sublimable solid.
(b) a liquid component from soluble impurities in the liquid component.
(c) a lighter liquid from a heavier liquid.
(d) a low boiling point liquid from a high boiling point liquid.
(e) solid constituents in a liquid constituent by adsorption.
Answer:
(a) By sublimation
Common salt + ammonium chloride on heating ammonium chloride sublimes common salt does not sublime and remains in the evaporating dish.
(b) By evaporation: Liquid is made to evaporate leaving behind the solid.
(c) By separating funnel: The heavier lower layer passes into the beaker on opening the stop-cock. Close the stop-cock as lighter layer reaches the tip. Lighter layer will remain in the funnel.
(d) By fractional distillation: Miscible low boiling point liquid will evaporate and is collected in the receiver, leaving behind the miscible high boiling point liquid in the flask.
(e) The method used is chromatography

Question 16.
Give –
(a) The principle involved in separation of the mixture
(b) The technique of separation for each of the following mixtures.
(1) Naphthalene and sodium chloride
(2) Common salt from a solution of common salt in water
(3) Pure water from impure water
(4) Kerosene and water
(5) Methyl alcohol and water
(6)Dyes of an ink
Answer:
(1) By Sublimation

Principle — Based on the differenc in sublimable and non- sublimable nature of solids.
Sublimation: It is the process of conversion of a solid directly into vapour and back to solid without passing through the liquid state.
Sublimable solids thus turn directly into vapour on heating and back to pure solid on cooling the vapours. The non- sublimable solid in the mixture thus remains behind.

Technique of Separation — The mixture of the sublimableand non-sublimable solids are heated in an evaporating dish covered with a funnel plugged at one end with cotton. Sublimable solid on heating sublimes and the vapours condense and collect in the pure form on the inner side of the funnel, from where the sublimable solid is scrapped off. Non-sublimable solid remains behind in the evaporating dish.
New Simplified Chemistry Class 7 ICSE Solutions - Elements, Compounds and Mixtures 8

 

(2) By Evaporation

Principle — Based on evaporation of the liquid component in a soluble solid-liquid mixture.
Evaporation – It is a method used for recovery of the soluble solid from a solution by heating the mixture slowly, in a porcelain crucible on a flame.
For smoother steady heating the porcelain crucible maybe kept in a sand bath [a shallow metallic dish filled with sand].

Technique of Separation — The soluble solid can be separated from its liquid component by allowing the liquid component to evaporate either on its own or by heating. The liquid component is lost to the atmosphere The soluble solid component remains behind in the evaporating dish
New Simplified Chemistry Class 7 ICSE Solutions - Elements, Compounds and Mixtures 9

(3) By Distillation

Principle — Based on the distillation of the liquid component in a soluble solid-liquid mixture.
Distillation — It is the process of converting a liquid into vapour by heating in a distillation flask & subsequent condensation of the vapour back into the liquid.
The method is used to separate a liquid from a soluble solid or pure liquid [water] from impure liquid [impure water].
Technique of Separation — The soluble solid can be separated from its liquid component or pure water from impure water by placing the mixture i.e. impure water in the distillation flask.
On heating the distillation flask
The solid or solid impurities in water remains behind in the distillation flask
The liquid or water vaporizes, condenses in the Liebig’s condenser and is collected in the receiver.
New Simplified Chemistry Class 7 ICSE Solutions - Elements, Compounds and Mixtures 10

(4) By Separating funne

Principle — Based on the separation of two in-miscible liquids, one heavy the other light.
Separating funnel – It is a pair-shaped or cylindrical bulb with a stock-cock fitted at its end. The immiscible liquids are allowed to stand in the separating funnel, till the heavier liquid settles below the lighter liquid.
Technique of Separation — The liquid-liquid mixture is added to the separating funnel and the funnel kept aside for sometime.
The heavier immiscible liquid settles down in the separating funnel and is then removed from below on opening the tap and collected out separately.
The lighter immiscible liquid remains above the heavier liquid, (immiscible liquids do not mix)
New Simplified Chemistry Class 7 ICSE Solutions - Elements, Compounds and Mixtures 11

(5) By Fractional Distillation

Principle — Based on the separation of mixture of two miscible liquids, with different boiling points.

Fractional distillation: It is the mixture of two miscible liquids with different boiling points is heated in a distillation flask when the two liquids separate out due to their difference in boiling points.

Technique of Separation – The mixture of two miscible liquids e.g. alcohol and water having different boiling points is taken in the distillation flask and heated slowly.
The mixture boils are the respective boiling points of the components and the component with the higher boiling point remains behind in the distillation flask condensation.The component with the lower boiling point collects in the receiver, after condensation in the Leibigs condenser.

The fractionating column contains several traps to allow the vapours of the higher boiling point components to condense, there by only the lower boiling point component enters the condenser and is collected in the receiver.
New Simplified Chemistry Class 7 ICSE Solutions - Elements, Compounds and Mixtures 12

(6) By Chromatography

Principle — Chromatography is-a method by which the various components of a mixture e.g. dyes in an ink, are separated due to their difference in rate of flow over an absorbent medium i.e. stationary phase e.g. filter paper under the influence of a solvent i.e. the mobile phase.
Chromatography — There are two phases and they are:
Stationary phase in chromatography, the adsorbent medium is known as the stationary phase e.g. filter paper made of cellulose.
Mobile phase the solvent or the solution that moves due to capillary action is known as the mobile phase.
Technique of Separation — Separation of dyes in ink by paper chromatography Ink prepared by dissolving different dyes e.g. A, B, C, D in a suitable solvent, is taken.A line is drawn with a pencil over a long strip of a filter paper.
Place the ink spot containing the different dyes on the filter paper as shown below.
The filter paper is then hung with its lower end dipped in a suitable solvent.
The solvent maybe a mixture of ethyl alcohol and water poured into a tall jar, such that only a small lower part of the jar is filled.
The paper strip with the spot of ink at its, is dipped into the solvent in a way that the spot itself remains above the liquid surface.
The solvent flows over the ink spot and the various components of the mixture, of dyes in the ink are separated as shown below.
New Simplified Chemistry Class 7 ICSE Solutions - Elements, Compounds and Mixtures 13

Objective Type Questions
Elements, Compounds & Mixtures

1. Select the correct answer from A, B, C, D and E for each statement given below:
A: Chalk    B: Oxygen   C: Silicon      D: Bromine   E: Nitrous oxide

An element present in the earth’s crust, atmosphere and human body.
Ans. B: Oxygen

The chemical name for dinitrogen oxide [N20].
Ans. E: Nitrous oxide

A compound containing carbon, oxygen and calcium.
Ans. A: Chalk

A metalloid.
Ans. C: Silicon

A non-metal which exists in the liquid state.
Ans. D: Bromine

2. Select the correct answer from the choice in bracket.

The least reactive metal, [magnesium/silver/copper]
Ans. silver.

The positively charged particle of an atom, [electron/ proton/neturon]
Ans. proton

The formula of caustic soda. [KOH/Ca(OH)./NaOH]
Ans. NaOH

The ideal method to separate iodine and KCI. [sublimation/ evaporation/distillation]
Ans. sublimation

A homogenous mixture, [brass/dust in air/chalk and water]
Ans. brass

3. Match the ideal method of separation of components in a mixture in List I with the – appropriate process in List II.
New Simplified Chemistry Class 7 ICSE Solutions - Elements, Compounds and Mixtures 14
New Simplified Chemistry Class 7 ICSE Solutions - Elements, Compounds and Mixtures 15
Answer:
New Simplified Chemistry Class 7 ICSE Solutions - Elements, Compounds and Mixtures 16

4. Give reasons for the following statements :

Question 1.
If fractional distillation is carried out using a liquid-liquid mixture, one liquid will remain in the flask and the other  will be collected in the receiver.
Answer:
The vapours of the higher boiling point components to condense, thereby only the lower boiling point component enters the condenser and is collected in the receiver.

Question 2.
Evaporation of a common salt solution or sea water, leaves behind common salt inside the evaporating dish after heating.
Answer:
The liquid component is lost to the atmosphere on heating the mixture in an evaporating dish.

Question 3.
Components in a mixture are present in varying proportions and not in a fixed proportion.
Answer:
A mixture is an impure substance containing more than one element or compound, mechanically mixed together in any proportion and the mixture retains the properties of its constituents i.e. elements or compounds.

Question 4.
Gunpowder is an example of a heterogenous mixture.
Answer:
Because Gun powder is produced by mixing two or more substances in any proportion by weight.

Question 5.
In chromatography the absorbent medium e.g. What man filter paper is known as the – stationary phase.
Answer:
Chromatography is a method by which the various components of a mixture e.g. dyes in an ink. What man filter paper is known as the stationary phase because it act as a substance that stays fixed inside the column.

5. Name the following: 

The non-sublimable solid from a mixture of iodine and potassium nitrate.
Ans. Potassium nitrate.

The heavier liquid component from – mercury and water.
Ans. Mercury.

The lower boiling point component from methyl alcohol and water.
Ans. Methyl alcohol.

The compound containing one atom of sulphur and two atoms of oxygen.
Ans. Sulphur dioxide.

An acid whose formula is ‘H2CO3’.
Ans. Carbonic acid

New Simplified Chemistry Class 7 ICSE Solutions – Physical and Chemical Changes

New Simplified Chemistry Class 7 ICSE Solutions – Physical and Chemical Changes

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Points to Remember: 

  1. All changes are classified into two types
    • Physical change
    • Chemical change.
  2. Physical Change— A physical change is a temporary change in which no new substance is formed and chemical composition remains same. e.g. Melting of ice.
  3. Chemical Change— A chemical change is a permanent change, in which a new substance is formed whose chemical composition and physical properties are different, e.g. Burning of a candle.
  4. Chemical Reaction— Any chemical change in matter involving its transformation into one or more new substances is called a chemical reaction.
  5. Chemical Equations—A chemical equation is the symbolic representation of a chemical reaction using the symbols and the formulae of the substances involved in the reaction.
  6. The substances that react with one another are called reactants, and the new substances thus formed are called products.
  7. A balanced chemical reaction is one in which the number of the atoms of each element on the reactant side is equal to the number of atoms of that element on the product side.
  8. The law of conservation of mass states that mass can neither be created nor be destroyed.
  9. A chemical equation gives both qualitative and quantitative information about reactants and products.
  10. The type of chemical reaction in which two substances combine to form a new substance is known as combination reaction.
  11. The type of chemical reaction in which a substance breaks up on heating to form two or more simpler substances, which can be either elements or compounds, known as decomposition reaction. 

ACTIVITIES & DEMONSTRATIONS

Demonstrations & Discussions – By the Teacher
Classifying – changes into physical & chemical with the help of charts or match the following or by putting X
New Simplified Chemistry Class 7 ICSE Solutions - Physical and Chemical Changes 1

EXERCISE

Question 1.
Change is the law of nature and occur in our everyday life, at all times and in all places.
Differentiate between the following changes with a suitable example.
(a) Desirable and undesirable change.
(b) Periodic and non-periodic change
(c) Slow and fast change.
(d) Natural and man-made change
(e) Reversible and irreversible change.
Answer:
(a) Desirable and undesirable change
New Simplified Chemistry Class 7 ICSE Solutions - Physical and Chemical Changes 2
(b) Periodic and non-periodic change
New Simplified Chemistry Class 7 ICSE Solutions - Physical and Chemical Changes 3
New Simplified Chemistry Class 7 ICSE Solutions - Physical and Chemical Changes 4
(c) Slow and fast change.
New Simplified Chemistry Class 7 ICSE Solutions - Physical and Chemical Changes 5
(d) Natural and man-made change
New Simplified Chemistry Class 7 ICSE Solutions - Physical and Chemical Changes 6

(e) Reversible and irreversible change.
New Simplified Chemistry Class 7 ICSE Solutions - Physical and Chemical Changes 7
New Simplified Chemistry Class 7 ICSE Solutions - Physical and Chemical Changes 8

 

Question 2.
Differentiate between a physical change and a chemical change with reference to –
(a) Nature of change e. temporary and reversible or permanent and irreversible.
(b) Formation of products.
(c) Energy change taking place during the respective change.
Answer:
New Simplified Chemistry Class 7 ICSE Solutions - Physical and Chemical Changes 9

Question 3.
Give three reasons why melting of wax, is considered a physical change while burning of a candle, a chemical change.
Answer:
Melting of wax is a temporary and reversible change on cooling, wax solidifies and no new product is formed while burning of candle is a permanent change i.e. products are not convertible, new substance is formed having different composition & different properties.

Question 4.
State the observations seen, when milk in a dish is kept aside for a few hours or more. Is the change which occurs – a physical change or a chemical change. Give reasons.
Answer:
On keeping aside – the milk in a dish for a few hours or more. The change observed – will be that the milk has changed into curd. The change is permanent and cannot be reversed. New substance curd is formed. It is a chemical change.

Question 5.
State what is meant by the term – inter conversion of matter. Is inter conversion of matter a physical change or a chemical change.
Answer:
Inter conversion of matter involves, matter changing from one state to another and back to its original state, by change in temperature or pressure. It is a physical change in which one state of matter changes into another state and back again to its original state.

Question 6.
Ice kept in a beaker, slowly melts and turns into water. The water in the beaker on solidification Le. freezing turns back to ice. Give four reasons why the change from ice to water and water back to ice is considered a physical change.
Answer:
Both change are physical changes since

  1. The change is – temporary
  2. It is a reversible change
    [heating and cooling reverse the change]
    heating of ice – turns it into water,
    cooling of ice – turns    it back into  ice
  3. No new products are formed since both ice and water are chemically  – ‘H20’
  4. Properties of the original substance are not altered.

Question 7.
Explain the term – ‘sublimation’. Is sublimation of naphthalene – a physical or a chemical change. Give reasons.
Answer:
It is the conversion of a solid – directly into gaseous [vapour] state and on cooling directly back to solid state – without changing into liquid state.
It involves a change of state-and hence it is a physical change.

Question 8.
Ammonium chloride is also a sublimable solid. Give a reason why sublimation of ammonium chloride involves a physical and a chemical change.
Answer:
Sublimation of ammonium chloride – [NH4C1]
Ammonium chloride sublimes on heating and dissociates into ammonia [NH3] and hydrogen chloride [HC1], which recombine on cooling to give back – NH4C1
New Simplified Chemistry Class 7 ICSE Solutions - Physical and Chemical Changes 10
Dissociation – is a chemical change.
Hence, sublimation of such substances involves both – a physical and a chemical change.

Question 9.
State why addition of sodium chloride to water is considered a physical change, while addition of dilute sulphuric acid to zinc is considered a chemical change.
Answer:
Addition of sodium chloride to water is considered as a physical change because it does not form any new substance . but when addition of dilute sulphuric acid is added to zinc. They forms zinc-sulphate hence it is considered as a chemical change.

Question 10.
Photosynthesis is a natural process by which green plants manufacture food in the presence of sunlight.
(a) Are any new products formed during the above process.
(b) Can the change be reversed or is irreversible.
(c) State the conclusions which can be drawn, to represent photosynthesis as a physical or a chemical change.
Answer:
(a) The change is permanent and new products are formed – i.e. glucose and oxygen.
(b) The change cannot be reversed. It is irreversible.
(c) Carbon dioxide and water cannot be obtained back from glucose and oxygen hence it is chemical change.

Question 11.
Give reasons why – separation of mixtures e.g. iron from a mixture of iron and sulphur is a physical change, but heating a mixture of iron and sulphur is considered a chemical change.
Answer:
Physical change

  1. There is no change in the specific properties of the constituents.
    Example: The particles of iron can be separated from sulphur with the help of a magnet or by dissolving sulphur in carbon disulphide.
  2. No new substance is formed.
    Example: The mixture of iron and sulphur does not form any new substance.
  3. There is not net release or absorption of energy.
    Example: When iron and sulphur particles are mixed, heat energy is neither given out nor absorbed.
  4. It is a temporary change and can be reversed by removing the cause of the change.
    Example: The particles of iron can be separated from the mixture with the help of a magnet. removing the cause of change.

Chemical change

  1. There is a specific change in the prorperties of the – constituents.
    Example: The particles of iron or sulphur cannot be separated by a magnet or carbon disulphide.
  2. A new substance is formed.
    Example: Iron sulphide is the new substance formed when iron and sulphur are heated.
  3. There is a net release or absorption of energy when a chemical change takes place.
    Example: When iron sulphide is formed, the test tube gets red hot on account of the release of a large amount of heat energy.
  4. It is a permanent change and cannot be reversed by removing the cause of the change.
    Example: The particles of iron can be separated from the mixture with the help of a magnet.removing the cause of change.

Question 12.
Explain in brief the involvement of energy in – physical and chemical changes.
Answer:
Involvement of energy in physical and chemical changes

  1. Physical changes use energy to change the state of matter,
  2. Chemical changes release or absorb energy when changing a substance into a new substance.
    Energy is released during a decomposition of a substance while energy is absorbed during formation of a new substance.

Objective Type Questions
Physical & Chemical Changes

1. Fill in the blanks with the appropriate words for each of the statements given below:

  1. Germination of seeds is considered a chemical change
  2. If a change is permanent & irreversible it is considered a chemical change
  3. Heating a piece of iron, is considered a physical change, while heating a piece of coal [carbon] is considered a chemical change
  4. Chemical changes may involve exchange of energy in the form of light and heat.
  5. Change of milk of curd is a desirable change

2. State whether the following statements are true or false. If false write – the correct statement.

  1. Desirable changes are meaningful, while undesirable changes are unfavourable.
    True.
  2. During physical changes, the composition of the original substance is not altered, but the properties of the original substance are altered.
    True.
  3. During a chemical change the composition of the original substance is not altered and the change is irreversible.
    False.During a chemical change the composition of the original substance is altered and the change is irreversible.
  4. Melting of butter and wax are examples of chemical changes.
    False. Melting of butter and wax are examples of physical changes.
  5. Melting of ice is an exothermic, irreversible chemical change.
    False. Melting of ice is an endothermic, reversible physical change.

3. Match the examples of changes in List I with the correct.
New Simplified Chemistry Class 7 ICSE Solutions - Physical and Chemical Changes 11
Answer:
New Simplified Chemistry Class 7 ICSE Solutions - Physical and Chemical Changes 12

4. Fill in the blanks with the correct words for each of the statements given below:

  1. Sublimation is considered a change of state of matter.
  2. Sublimation involves a physical change
  3. During sublimation a solid on heating turns directly into vapour and on cooling back to solid.
  4. Ammonium chloride, a sublimable solid undergoes dissociation on heating.
  5. Sublimation of iodine is an example of physical change

5. Name the following:

  1. The product/s obtained during ‘photosynthesis’ – which is a chemical change.
    Ans. Glucose and Oxygen.
  2. The term involved in the change of state from – ‘water to ice’ – which is a physical change.
    Ans. Freezing Point.
  3. The final product of the physical change involved during ‘melting of a piece of wax’.
    Ans. Wax [CxHy]
  4. The type of change e. physical or chemical involved – ‘during respiration in human beings’.
    Ans. Chemical Change.
  5. The type of change physical or chemical involved – ‘when a substance undergoes a change in state, colour or size’.
    Ans. Physical Change.

New Simplified Chemistry Class 7 ICSE Solutions – Matter and Its Composition

New Simplified Chemistry Class 7 ICSE Solutions – Matter and Its Composition

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

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Points to Remember:

  1. Matter has mass and occupies space.
  2. Matter is made up of atoms and molecules.
  3. Atoms are the smallest particles of matter which may or may not have independent existence.
  4. 4. Molecules are capable of independent existence. They are
  5. made up of atoms of same kind or different kinds.
  6. The atoms and molecules are in random motion.
  7. There are gaps between the molecules of matter called as intermolecular space.
  8. There exists a force of attraction between the molecules
  9. known as intermolecular force of attraction.
  10. Matter exists in three states : solids, liquid and gas.
  11. Matter can change from one state to another on changing temperature and pressure.
  12. The change of state of a matter from one form into another I is called inter conversion of states of matter.

EXERCISE

Question 1.
Explain the meaning of the term matter with special reference to the term ‘substance’.
Answer:
Matter is the basic substance of which all materials, living or non-living are made of.

Question 2.
Name the three states of matter. On what basis are the three states classified.
Answer:
Three states of matter are:

  1. Solid
  2. Liquid
  3. Gases

Basis of the classification are:
Physical properties like:

  1. Mass
  2. Volume
  3. Shape
  4. Rigidity
  5. Density
  6. Arrangement of particles.

Question 3.
Each of the three states of matter has mass. Explain with the help simple experiments – that each state of matter has mass.
Answer:
Matter i.e. solids, liquids and Gases have mass explained by the following experiments.
(1) Solid
Experiment: A solid placed on one side of the scale, causes the scale to tilt towards one side.
Conclusion: The scale tilts due to the mass of the solid, hence all solids have mass.
New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 1

(2) Liquid:         
Experiment: A liquid placed on one side of the scale, causes the scale to tilt towards one side.
Conclusion: The scale tilts due to the mass of the liquid, hence all liquids have mass.
New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 2

(3) Gas:
Experiment: An inflated balloon placed on one side of the scale causes it to tilt towards one side.
Conclusion: The scale tilts due to the mass of the gas, hence all gases have mass.
New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 3

Question 4.
A measuring cylinder is filled with water to a particular mark. A piece of solid is immersed inside the measuring cylinder. State why the level of water in the measuring cylinder will rise up. If the solid is removed, what will be the new level of the water in the measuring cylinder. Give a reason for your answer.
Answer:
When a piece of solid stone is immersed inside the measuring cylinder. The water level rises up.
New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 4
On removal of solid stone the water level in the measuring cylinder falls down back to the mark ‘A’.
New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 5

Hence, It show that the stone occupies the space of the water and thus pushes the water level up. This experiment or procedure also proves that all solids occupy space.

Question 5.
A glass beaker is half filled with water and an empty glass tumbler is inverted & lowered inside the glass beaker. State your observations on tilting the tumbler below the level of the water in the glass beaker. Give a reason for your answer.
Answer:
(1) Take a glass beaker half-filled with water as shown in diagram.
New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 6
(2) Take an empty glass tumbler which contains air is inverted and lowered inside the glass beaker.
New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 7
(3) On tilting the tumbler the air inside the tumbler is displaced and bubbles of air are seen coming out. The air is pushed out by the water on tilting the tumbler inside the beaker of water.This experiment or procedure also proves that air or gases occupy space
New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 8

Question 6.
Differentiate the general properties of solids, liquids and gases in the form of a table — with reference to
(a) mass (b) space  (c) volume (d) shape  (e) compressibility (f) density (g) free surfaces (h) diffusion.
Answer:
(a)
Solids— They have mass
Liquid — They have mass
Gases— They have mass

(b)
Solids— They Occupies space
Liquid— They Occupies space
Gases— They Occupies space

(c)
Solids-They have a definite volume
Liquid-They have a definite volume
Gases-They have no definite volume

(d)
Solids-They have a definite shape
Liquid-They have no shape
Gases-They have no shape

(e)
Solids-They have a no compressibility
Liquid-They have  slight compressibility
Gases-They have high compressibility

(f)
Solids-They have high density
Liquid-They have less density
Gases-They have least density

(g)
Solids-They have any number(of free surfaces)
Liquid-They have one free surfaces
Gases-They have no free surfaces

(f)
Solids-They have no diffusibility
Liquid-They have slight diffusibility
Gases-They have high proper diffusibility

Question 7.
State in which of the three states of matter- 
(a) Are the atoms or particles far apart
(b) The space between the particles is minimum.
(c) The force of attraction between the particles is very weak.
(d) The movement of the particles are neither about their own positions nor in any random direction.
Answer:
(a)
Gas  (b)  Solid  (c)  Gas  (d)  Gas

Question 8.
Give a reason why –
(a) Solids have a definite volume & a definite shape.
(b) Liquids have a definite volume but no definite shape.
(c) Gases have no definite volume and no definite shape.
Answer:
(a)
Any matter that is a solid has a definite shape and a definite volume. The molecules in a solid are in fixed positions and are dose together. Although the molecules can still vibrate, they cannot move from one part of the solid to another part. As a result, a solid does not easily change its shape or its volume.
(b)
Any matter that is a liquid has a definite volume but no definite shape. The molecules in a liquid are less closely packed and they have space between them as compared to solids. Although the molecules can easily move. The inter molecular forces of attraction between the particles are less strong as compared to solids. Hence liquid does have fixed shape and takes the shape of the container in which it is placed e. It has definite volume.
(c)
Any matter that is a gas has no definite volume and no definite shape. The molecules in a gas are least closely packed and inter molecular space between them is very large when compared to solids & liquids. The inter molecular force of attraction between the particles are negligible. As a result a liquid does not easily change its shape nor they have fixed volume.

Question 9.
Particles of matter possess energy due to their random motion. Compare the particles in a solid, -liquid & in a gas with reference to the amount of kinetic energy possessed by each.
Answer:
Particles of matter possess energy due to random motion is called kinetic energy.
Comparison of particles in a solid, liquid and gas with reference to kinetic energy are given in the following:
New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 9

Question 10.
Describe simple experiments to show that –
(a) particles of matter have inter molecular attraction
(b) particles of matter are closely packed in solids and less in liquids.
Answer:
(a) Experiment – To show that particles off matter have inter molecular attraction
New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 10

Procedure:

  1. Globules of mercury are placed in a petri dish and kept at – a distance.
  2. The petri dish is shaken slowly and the mercury globules come together forming a big globule.
    Conclusion — The above experiment concludes that a force of attraction exist between particles of matter.

(b) Experiment – To show that particles are closely packed in solids and less in liquids

New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 11

Procedure:

  1. Take a measuring cylinder and add 100 ml. of water to it.
  2. Add crystals of sugar [solid] to the water and stir carefully to obtain a sugar solution.
  3. The volume of water after addition of sugar remains the
    same i.e. at the 100 ml. mark.

Conclusion

  1. Particles of a liquid [e.g. water] are less closely packed.
  2. Particles of a solid [e.g. sugar] are closely packed.
  3. The sugar particles fill the inter molecular spaces, which must be existing between the water molecules and hence the level of water in the measuring cylinder does not rise.

Question 11.
A crystal of iodine is placed in a closed flat bottom flask and heated. State how you would conclude from the observations seen, that inter particle space is minimum in solids and maximum in gases.
Answer:
Procedure:

  1. 40 A crystal of iodine is heated in a closed flask. The crystal containing ‘X’ no. of particles turns into vapours, which also contain ‘X’ no. of particles and fills the complete flask.

Conclusion

  1. Particles of a solid [e.g. crystal of iodine] are more closely packed.
  2. Particles of a gas [e.g. vapours of iodine] are least closely packed and fill the flask completely.

New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 12

Question 12.
Explain the term ‘inter conversion of matter’ – with ice as a starting material. State the term which refers to the conversion of a substance on heating from.
(a) solid state to liquid state
(b) liquid state to vapour state
(c) vapour state to liquid state
(d) liquid state to solid state.
Answer:
The phenomenon of change from one state to the other and then back to the original state without any change in its chemical composition is called ‘inter conversion of matter.’
The terms which refers to the conversion of a substance are:
(a) Melting
(b) Vaporisation
(c) Liquefaction
(d) Solidification

Question 13.
Give a reason why solids and liquids co-exist at their melting points.
Answer:
A substance exists in the solid state below its melting point and in the liquid state above its melting point. Hence, solids and liquids co-exist at their melting point.

Objective Type Questions
Matter and its composition

Question 1.
Match the characteristics of the three states of matter in List I with their correct answer from List II.
New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 13

Answer:
New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 14

Question 2.
Select the correct answer from the choice in bracket to complete each sentence:

  1. Matter is defined as anything that occupies space and has mass
  2. The three states of matter are classified on the basis of differences of certain physical.   
  3. Matter made up of one kind of particles is said to be homogeneous.
  4. Particles in a gas possess very large kinetic energy.
  5. The inter molecular force of attraction is maximum in solids.

Question 3.
Give reasons for the following.

  1. Gases have no definite shape or volume.
  2. Liquids have one free upper surface only.
  3. Globules of mercury kept in a petri dish, which is shaken slowly, come together forming a big globule.
  4. A crystal of iodine on slow heating in a closed flask, turns into vapours and fills the complete flask.
  5. An empty tumbler lowered into a glass beaker containing water, on tilting shows bubbles of air coming out, but when not tilted, no bubbles are seen.

Answer:

  1. Any matter that is a gas has no definite volume and no definite shape. The molecules in a gas are least closely packed and inter molecular space between them is very large when compared to solids & liquids. The inter molecular force of attraction between the particles are negligible. As a result a liquid does not easily change its shape nor they have fixed volume.
  2. Liquids have one free upper surface only because as liquids have a definite volume but no shape and while liquids are bounded by the container, they are placed in and have only one free surface, the upper surface.
  3. This is because the air is being pushed out by the water on tilting the tumbler inside the beaker of water. Air or gases occupy space.

Question 4.
State the correct term from A, B, C, D, E or F in List II which represents the – change of state of matter or its relevant property from List I
New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 15

Answer:
New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 16

Question 5.
Match the arrangement of atoms in the three states of matter in List I with the correct state in List II.
New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 17
Answer:
New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 18