Acids

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

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Viraf J Dalal Chemistry Class 10 Solutions and Answers

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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:

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 + 2HNO₃ → Pb(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:

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:

Answer:

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:

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.

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:

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)

(2)

(3)

(4)

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:

2012

Question 1.

Match the following:

Answer:

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 + H₂SO₄ → Na₂SO₄ + H_zO + CO₂
   
   
2. Zinc carbonate
   Zn(NO₃)₂ + Na₂CO₃→ ZnCO₃ + 2NaNO₃
3. Copper (II) sulphate
   CuCO₃ + H₂SO₄ → CuSO₄ + h₂o + CO₂
4. Iron (II) sulphate.
   Fe + H₂SO₄ → 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:

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:

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:

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.

(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.

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.

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].

(2) Strong Alkali – Is an alkali which dissociates – almost completely in aqueous solution thereby producing a – high concentration of hydroxyl [OH^–] ions.

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.

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:

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.

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.

(2)
It ionises in two steps in aqueous solution as shown below:

(3)
It forms two types of salt, e., normal salt and acid salt as shown below:

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

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

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).

Question 11.

State how you would obtain:

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

Answer:
(1)

(2)

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

(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,

(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.

(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,

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:

(2) Reaction of cone. H₂SO₄ with metallic nitrate

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.

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.

(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,

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,

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:

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

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. K₂CO₃ is 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

2. An example of a base which is not a alkali is….. (caustic soda / zinc hydroxide / liquor ammonia / caustic potash)
   Ans. Zinc hydroxide

3. An example of a strong acid is dilute……… (acetic acid / sulphuric acid / tartaric acid / carbonic acid)
   Ans. Sulphuric acid

4. An example of a weak alkali is…. (potassium hydroxide / calcium hydroxide / sodium hydroxide) solution.
   Ans. Calcium Hydroxide

5. An acid having basicity 1 is……… (carbonic acid / acetic acid / sulphurous acid)
   Ans. Acetic acid

6. An acid obtained by dissolving sulphur trioxide in water is…. (sulphurous acid / sulphuric acid oleum)
   Ans. Sulphuric acid

7. A volatile acid obtained when nitre reacts with non­volatile concentrated sulphuric acid on heating is (hydrochloric acid / sulphuric acid/ nitric acid)
   Ans. Nitric acid

8. A base obtained when lead nitrate undergoes thermal decomposition is……. (trilead tetroxide / lead (IV) oxide/ lead (II) oxide.                                                        .
   Ans. Lead (II) oxide

9. An acid obtained when concentrated nitric acid is heated with sulphur is…….. (sulphurous acid / sulphuric acid / nitrous acid)
   Ans. Sulphuric acid

10. The more volatile acid obtained when the less volatile acid reacts with sodium bicarbonate is……… (sulphuric acid / carbonic acid / nitric acid)
    Ans. Carbonic acid

11. 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.

12. A solution whose pH is above 7 is….. (vinegar / milk / liquor ammonia.
    Ans. Liquor Ammonia

13. The salt formed when sulphuric acid reacts with excess caustic soda solution is…… (sodium bisulphite / sodium sulphate / sodium sulphite / sodium bisulphate).
    Ans. Sodium sulphate

14. An example of an acid salt is……. [CH₃COONa/NaNO₃/ Na₂HPO₄/NaKCO₃]
    Ans. Na₂HPO₄

15. An example of a soluble salt is ……… (AgCl / PbSO₄ /CaSO₄ / CaCl₂)
    Ans. CaCl₂

16. An example of an insoluble salt is….. (Na₂CO₃ \ K₂CCl,/ MgCO₃ / (NH₄)₂ CO₃)
    Ans. MgCO₃

17. A salt prepared by neutralization in which titration is involved is…….. (MgCl₂ / CaCl₂ / NH,Cl / CuCl₂)
    Ans. NH₄Cl
18. An insoluble salt prepared by direct combination or synthesis is……. [FeCl₃ / FeSO₄ / FeS/Fe(NO₃)₂] Ans. FeS

19. A salt prepared by precipitation i.e. by double decomposition of two salt solutions is………… (Na₂SO₄ /PbSO₄ / ZnSO₄ / CuSO₄)
    Ans. PbSO.
20. A salt prepared by simple displacement i.e. action of dilute acid on a metal is____ (PbCl₂/ CuCL, / AlCl₃ / HgCl)
    Ans. AlCl₃
21. Decomposition of calcium hydrogen carbonate with…. [dil. HNO₃ /dil. HCl/dil. H₂SO₄] results in formation of calcium chloride.
    Ans. dil.HCl

22. Action of dilute acid on a metallic sulphide results in evolution of____ [SO₂/H₂S/CO₂] gas.
    Ans. H₂S

23. 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.

2. A normal salt of sodium formed from acetic acid.
   Ans. Sodium acetate, COCOON a.
3. 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].

4. An ion which combines with a polar covalent molecule to form an ammonium ion.
   Ans. Hydrogen ion a proton (H⁺).

5. 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

2. An acid which dissociates to give a low concentration of H⁺
   Ans. Weak acid

3. An acid containing hydrogen and a non-metallic element other than oxygen.
   Ans. Hydracids.

4. The type of acid which generally displaces another acid when the acid is heated with a salt.
   Ans. Less volatile acid

5. 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:

2. Calcium oxide → Calcium chloride → Calcium carbonate
   Ans. CaO + 2HCl → CaCl₂ + H₂O
3. Zinc sulphide Zn→ Zinc sulphate
   Ans. Zn + S → ZnS
4. Iron (II) chloride ← Fe→ Iron (III) chloride
   Ans. Fe + 2HCl → FeCl₂ + H₂
5. Lead (II) oxide → Lead nitrate→ Lead sulphate
   Ans. PbO + 2HNO₃ → Pb(NO₃)₂ + H₂O
6. 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.

1. Name the apparatus ‘A’.
   Ans. Burette

2. Name the substance ‘X’ placed in ‘A’ and the (substance ‘Y’ placed in B.
   Ans. Dil. H₂SO₄ Sodium Hydroxide

3. 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.

4. State which solution is transferred to the evaporating dish and evaporated to point of crystallisation for obtaining the salt.
   Ans. Sodium Sulphate.

5. 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,H₂SO₄ is a covalent compound as shown below.

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:

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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