Pure Substances and Mixtures Separation of Mixtures ICSE Class-6th Concise Selina Chemistry  Solutions Chapter-5. We Provide Step by Step Answer of Objective, True False , Fill in the blanks , Match the following , Short/Long Answer Type of Exercise-5 Pure Substances and Mixtures Separation of Mixtures . Visit  official Website  CISCE  for detail information about ICSE Board Class-6.

## Pure Substances and Mixtures Separation of Mixtures ICSE Class-6th Concise Selina Chemistry Solutions

### EXERCISE – I

#### Question 1.

Select homogeneous and heterogeneous mixtures from the following:
Salt solution, petrol and water, sand and charcoal, alcohol and water, air dissolved in water, air, sea water, fruit juices, mist, brass.
Homogeneous mixture : Salt solution, alcohol and water, air dissolved in water, sea water, brass.
Heterogeneous mixture: Sand and charcoal, air, fruit juice, mist, petrol and water.

#### Question 2.

Define the following :

(a) Pure substance
(b) Impure substance
(c) Alloy
(d) Solution
(e) Heterogeneous mixture
(f) Homogeneous mixture

##### (a) Pure substance :

“Pure Substance is either element or compound. It contains the same kind of atom or molecules and has a definite set of physical and chemical properties.”

##### (b)Impure substance :

“A substance in which some other substances are also present in smaller or larger amounts is called an impure substance. Mixtures are impure substance.

Example of impure substance is air.

##### (c) Alloy :

“A homogeneous solid mixture of two or more metals or a metal and a non-metal is called an alloy.”

##### (d) Solution :

“The homogeneous mixture of water (or any other solvent) and a substance soluble in it is called a solution.”

##### (e) Heterogeneous mixture :

“A mixture in which the components are not uniformally distributed through its volume and can be easily seen separately is called heterogeneous mixture.”

##### (f) Homogeneous mixture :

“A mixture in which its constituents are uniformly distributed throughout its volume and cannot be seen separately is called a homogenous mixture.”

#### Question 3.

List four characteristics of a mixture.
Four characteristics of a mixture :

1. Mixture has no fixed composition.
2. To form a mixture energy is neither produced nor evolved.
3. Mixture has no fixed melting’point and boiling points.
4. Mixture retain the properties of its components.
5. Components of mixtures can be seperated by simple physical methods.

#### Question 4.

##### Give reasons :

(a) Why do sugar and water retain their individual properties in a sugar solution ?
(b) Why do petrol and water form a heterogeneous mixture ?
(c) Why sulphur does dissolve when carbon disulphide is added to a mixture of iron and sulphur but not when it is added to iron sulphide ?

##### (a)

As sugar solution is a mixture and mixtures has not any specific set of properties. They show the properties of the individual components from which they are formed.

##### (b)

Petrol and water forms a heterogeneous mixture as its constituents can be seen separately and are not uniformly distributed throughout its volume.

##### (c)

Sulphur has the property to dissolve in carbon disulphide whereas iron does not dissolve and retains its individual property. However, On heating Iron and Sulphur, they chemically combined forming Iron Sulphide. In this, Iron and Sulphur particles do not exists separately as such they loose their individual property.

#### Question 5.

Give two examples for each of the following types of mixture.

(a) solid-solid
(b) solid-liquid
(c) liquid-gas
(d) gas-gas

Two examples of :
(a) solid – solid

1. sand and sugar
2. sand and iron filling.

(b) solid – liquid –

1. salt and water
2. charcoal and water.

(c) liquid – gas –

1. coca cola
2. mist.

(d) gas – gas –

1. air
2. helium and hydrogen in air balloon,
3. perfumes and air.

#### Question 6.

Name the components present in the following mixtures:

(a) Brass
(b) Duralumin
(c) Tap water
(d) Bronze
(e) Crude petroleum oil .

(a) Brass → Copper and Zinc.
(b) Duralumin → Aluminium + Copper with little manganese and magnesium.
(c) Tap water → air, dissolved salts.
(d) Bronze → Copper, Tin and zinc.
(e) Crude petroleum oil → petrol, kerosene, diesel, LPG, mixed with salt, water and earth particles.

#### Question 7.

State:

(a) Three differences between water and air.
(b) Four differences between compounds and mixtures.

##### (a)

Water :

1. The components of water are hydrogen and oxygen which are chemically combined in a fixed ratio of 1 : 8 by mass.
2. The chemical composition of water remains same from whatever source it is obtained.
3. The properties of water are completely different from the properties of elements from which it is formed i.e. hydrogen and oxygen.
4. Energy change occurs in the formation of water.
5. A molecule of water is represented by a definite formula H2O.
##### Air :
1. The main components of air are nitrogen, oxygen, carbon -dioxide, water vapour which are not chemically combined.
2. The composition of air varies from place to place. During rainy season the air becomes humid due to presence of more water vapour. Some impurities like sulphur dioxide, hydrogen sulphide etc. also changes its composition at some places.
3. The components of air retain their individual properties but not air.
4. No energy change occurs when components of air are mixed together.
5. Air cannot be represented by any chemical formula.
##### Compound :
1. A compound is a pure substance.
2. Compounds are always homogeneous.
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.
4. Formation of a compound involves change in energy.
5. Compounds have specific set of properties.
6. Components of compounds can be separated only by complex chemical processes.
##### Mixture :
1. A mixture is an impure substance.
2. Mixtures may be homogeneous or heterogeneous.
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 mixture does not involve any change in energy.
5. Mixtures do not have any specific set of properties.
6. Components of mixtures can be separated by simple physical methods.

### EXERCISE – II Pure Substances and Mixtures Separation

#### Question 1.

Define:

(a) Filtration
(b) Sublimation
(c) Evaporation
(d) Crystallisation
(e) Miscible liquids
(f) Immiscible liquids

##### (a) Filtration :

The process of separating solid particles from liquid by allowing it to pass through a filter paper is called filtration.

##### (b) Sublimation :

The process in which a solid changes directly into its vapours on heating is called sublimation.

##### (c) Evaporation :

Is the process of converting a liquid into its vapours state either by exposing it to air or by heating.

##### (d) Crystallisation :

Evaporation of liquid from a homogeneous liquit-solid mixture and collecting solid in the form of crystals is called
crystallisation.

##### (e) Miscible liquids:

Homogeneous liquid-liquid mixtures are called miscible liquids.

##### (f) Immiscible liquids :

Heterogeneous liquid-liquid mixtures are called immiscible liquids.

#### Question 2.

Why do we need pure substances?
We need pure substances because of the following reasons:

1. A pure substance has a fixed melting and fixed boiling point.
2. A pure substance has its characteristic taste, colour and odour.
3. Pure substances can not be broken further into more simple substances by any physical means.

#### Question 3.

Give one example for each of the following types of mixtures.

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