Compounds and Mixtures

Selina Concise Chemistry Class 7 ICSE Solutions – Elements, Compounds and Mixtures

by

Selina Concise Chemistry Class 7 ICSE Solutions – Elements, Compounds and Mixtures

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 7 Chemistry. You can download the Selina Concise Chemistry ICSE Solutions for Class 7 with Free PDF download option. Selina Publishers Concise Chemistry Class 7 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 7 Chemistry ICSE SolutionsPhysicsBiologyMathsGeographyHistory & Civics

Selina Concise ICSE Solutions for Class 7 Chemistry Chapter 3 Elements, Compounds and Mixtures

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— 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 – I

Question 1.
Write the symbols of helium, silver, krypton, antimony, barium.
Answer:

Element                   Symbol
Helium                         He
Silver                            Ag
Krypton                       Kr
Antimony                    Sb
Barium                        Ba

Question 2.
Write the names of following elements Na, C, Kr, U, Ra, Fe, Co.
Answer:

Symbol           Element
Na                        Sodium
C                          Carbon
Kr                        Krypton
U                         Uranium
Ra                        Radium
Fe                           Iron
Co                        Cobalt

Question 3.
Define :

  1. Elements : An element is the basic form of matter that cannot be broken down into simpler substances by chemical reactions.
  2. Compounds : A compound is a pure substance formed by the chemical combination of two or more elements in a fixed ratio by mass.

Question 4.
Name the main metal present in the following :
Answer:

(a) Haemoglobin                                    Iron
(b) Chalk                                               Calcium
(c) Chlorophyll                                   Magnesium
(d) Chocolate wrappers                    Aluminium

Question 5.
Give four examples of non-metallic elements.
Answer:
Examples : Hydrogen, oxygen, nitrogen, carbon, chlorine, sulphur, phosphorus, etc.

Question 6.
What do you understand by :
Answer:

  1. Metalloids : Metalloids are those substances which have some properties of metals and some of non-metals e.g. boron, silicon.
  2. Noble gases : Noble gases are those which do not react chemically with other elements or compounds e.g. helium, neon, etc.

Question 7.
Select elements and compounds from the following list: Iron, plaster of paris, chalk, common salt, copper, aluminium, calcium oxide, cane sugar, carbon, silica, sodium sulphate, uranium, potassium carbonate, silver, carbon dioxide.
Answer:
Selina Concise ICSE Solutions for Class 7 Chemistry Chapter 3 Elements, Compounds and Mixtures-7

EXERCISE – II

Question 1.
State four difference between compounds and mixtures.
Answer:

CompoundMixture
1. A compound is a pure substance.1. A mixture is an impure substance.
2. Compounds are always homogeneous.2. Mixtures may be homogeneous or heterogeneous.
3. A compound has a fixed composition, i.e., it is formed when two or more pure substances chemically combine in a definite ratio by mass.3. A mixture has no fixed composition, i.e., it is formed by mixing two or more substances in any ratio without any chemical reaction.
4. Formation of a compound involves change in energy.4. Formation of a mixture does not involve any change in energy.
5. Compounds have specific set of properties.5. Mixtures do not have any specific set of properties.
6. Components of compounds can be separated only by complex chemical processes.6. Components of mixtures can be separated by simple physical methods.

 Question 2.
What are the characteristic properties of a pure substance? Why do we need them?
Answer:
Pure substance : Pure substances have a definite set of properties such as boiling point, melting point, density, etc. They are all homogeneous i.e., their composition is uniform throughout the bulk. Both elements and compounds are pure substances.
Pure substances are needed to :

  1. Manufacture medicines.
  2. To prepare chemicals in industry.
  3. For scientific purposes.
  4. To maintain the good health of human beings.

Question 3.
Give two examples for each of the following :
(a) Solid + Solid mixture
(b) Solid + Liquid mixture
(c) Liquid + Liquid mixture
Answer:
(a) Solid + Solid mixture :Sand and sugar,

  • Sand and stone,
  • sand and sugar.

(b) Solid + Liquid mixture :

  • Sand and water,
  • Charcoal and water.

(c) Liquid + Liquid mixture :

  • Oil in water,
  • Alcohol and water.

Question 4.
Define :

  1. Evaporation : Is the process ~of converting a liquid into its vapours state either by exposing it to air or by heating.
  2. Filtration : The process of separating solid particles from liquid by allowing it to pass through a filter paper is called filtration.
  3. Sublimation : The process in which a solid changes directly into its vapours on heating is called sublimation.
  4. Distillation : Distillation is the method of getting a pure liquid from a solution by evaporating and then condensing the vapours.
  5. Miscible liquids : Homogeneous liquid-liquid mixtures are called miscible liquids.
  6. Immiscible liquids : Heterogeneous liquid-liquid mixtures are called immiscible liquids.

Question 5.
Name the process by which the components of following mixtures can be separated.

  1. Iron and sulphur
  2. Ammonium chloride and sand
  3. Common salt from sea water
  4. Chaff and grain
  5. Water and mustard oil
  6. Sugar and water
  7. Cream from milk

Answer:

  1. Magnetic separation.
  2. Sublimation.
  3. Evaporation.
  4. Winnowing separates chaff (lighter) from heavier grains in two different heaps.
  5. Mustard oil and water is liquid-liquid immiscible mixture and is separated by separating funnel. Water being the heavier forms the lower layer.
  6. By evaporation in this process of converting a liquid into its vapour state by heating. Liquid is heated and water evaporate and sugar is obtained.
  7. Centrifugation.

Question 6.
How will you separate a mixture of common salt, chalk powder and powdered camphor? Explain.
Answer:
Comphor with sublimation. Chalk powder by Alteration then the residual left is common salt.

Question 7.
How is distillation more advantageous than evaporation?
Answer:
The advantage of distillation is that both components of the
solid and liquid mixture are obtained. Whereas in evaporation only solid is obtained.

Question 8.

  1. What is chromatography?
  2. Why is it named so?
  3. What are the advantages of chromatography?
  4. Name the simplest type of chromatography?
  5. On what principle is this method based?
  6. What is meant by stationary phase and mobile phase in chromatography?

Answer:

  1. The process of separating different dissolved constituents of a mixture by their absorption on an appropriate material is called chromatography.
  2. It is named so, because earlier it was used to separate mixtures containing coloured components only but these days this technique is applied to colourless substances too.
  3. Advantages of chromatography :
    (i) A very small quantity of the substance can be separated.
    (ii) Components with very similar physical and chemical properties can be separated.
    (iii) It identifies the different constituents of a mixture.
    (iv) lt also helps in quantitative estimation of components of a mixture.
  4. The simplest type of chromatography is “Paper chromatography”.
  5. Chromotography is based on differential affinities of compounds towards two phases i.e. stationary and mobile phase.
  6. The filter paper acts as “stationary phase” while the solvent act as “mobile phase”.

Question 9.
On what principle are the following methods of separation based? Give one example of a mixture for each of the methods mentioned in which they are used
Answer:

  1. Sublimation : Change of solid into vapours directly on heating and change of vapours into solid again on
    Example : Salt from ammonium chloride.
  2. Filtration : The process of separating insoluble solid particles from a liquid by allowing it to pass through a filter is called Alteration. These filters allow liquids to pass through them but not solids. The insoluble solid left on the filter is called the residue, while the liquid which passes through the filter is called the filtrate. Mixtures like chalk and water, clay and water, tea and tea leaves, sawdust and water, etc., are separated by this method.
  3. Sedimentation and decantation : The settling down of suspended, insoluble, heavy, solid particles in a solid- liquid mixture when left undistrubed is called sedimentation.
    The solid which settles at the bottom is called sediment while the clear liquid above it is called supernatant liquid.
    The process of pouring out the clear liquid, without disturbing the sediment, is called decantation.
    Example : A mixture of sand and water.
  4. Solvent extraction method : This method is used when one of the solid components is soluble in a liquid.
    Example : A mixture of sand and salt can be separated by this method. Salt gets dissolved in water while sand settles down in the container. The salt solution is then decanted. Salt is separated from the solution by evaporation. In this way, they can be separated.
  5. Magnetic separation : This method is used when one of the components of the mixture is iron. Iron gets attracted towards a magnet and hence can be separated. Mixtures of iron and sulphur, iron and sand, etc., can be separated by moving a magnet over them. Iron gets attached to the magnet and is separated.
  6. By using a separating funnel : It is a simple device used to separate the components of a liquid-liquid heterogeneous mixture.
    Example : Kerosene oil and water. The mixture is placed in a separating funnel and allowed to stand for sometime. The components form two clear layers. Water being heavier forms the lower layer and oil being lighter forms the upper layer. When the stopper of the funnel is opened, the heavier liquid trickles out slowly and is collected in a vessel. The stopper is closed when the bottom layer is entirely removed the funnel. In this way, the two liquids are separated.
  7. Fractional distillation : The process of distillation is used for separating the components of a homogeneous liquid-liquid mixture, like water and alcohol. This is based on the fact that alcohol boils at a lower temperature than water. The vapour of alcohol are collected and cooled while water is left behind in the original vessel. Thus, two liquids having different boiling points can be separated by distillation provided that difference in their boiling points must be 25 °C or more.

OBJECTIVE TYPE QUESTIONS

Question 1.
Fill in the blanks:
Answer:

  1. Elements are made up of same kind of atoms.
  2. Elements and compounds are pure substances.
  3. In a mixture the substances are not combined chemically.
  4. Clay is separated from water by the method called loading and decantation.
  5. Crystallisation is a process to obtain a very pure form of a solid dissolved in a liquid.
  6. Camphor and ammonium chloride can sublimate.

Question 2.
Give one word answers for the following :
Answer:

  1. The solid particles which remain on the filter paper after the filtration residue.
  2. The liquid which evaporates and then condenses during the process of distillation distillate.
  3. The process of transferring the clean liquid after the solid settles at the bottom of the container decantation.
  4. The process by which two miscible liquids are separated fractional distillation.

MULTIPLE CHOICE QUESTIONS

Select the correct alterative from the choices given for the following statements:
Question 1.
A pure liquid is obtained from a solution by :
Answer:

  1. evaporation
  2. distillation
  3. Alteration
  4.  crystallisation

Question 2.
Components of crude petroleum can be separated by :
Answer:

  1. distillation
  2. evaporation
  3. filtration
  4. fractional distillation

Question 3.
Example of a homogeneous mixture is :
Answer:

  1. tap water 
  2. distilled water
  3.  sand and water
  4. water and oil

Question 4.
In chromatography the filter paper is :
Answer:

  1.  stationary phase 
  2. mobile phase
  3. mixture
  4. none of the above

Question 5.
A set of mixture is :
Answer:

  1.  ink, honey, icecream, milk
  2. tapwater, gold, common salt, alloy
  3.  milk, brass, silver, honey
  4. butter, petroleum, tapwater, iron

 

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

by

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

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

Simplified ChemistryChemistryPhysicsBiologyMathsGeographyHistory & Civics

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