ICSE Living Science Chemistry for Class 6 Solutions Chapter 4 Pure Substances and Mixtures

Check Your Progress

Answer these questions.
Question 1.
Is gold a pure substance ?
Answer:
Yes, gold is an element which is made up of only one kind of atom (gold atoms). Therefore, gold is a pure substance.

Question 2.
Is milk a mixture or a compound ?
Answer:
Milk is a mixture as its constituents may be present in any proportion.

Question 3.
What type of mixture is formed when chalk powder and water are mixed uniformly ?
Answer:
Heterogeneous mixture (suspension)

Question 4.
Classify the following as homogeneous and heterogeneous mixtures.
a. Common salt solution
b. Dusty air
c. Muddy water
d. Brass
Answer:
a. Homogeneous mixture
b. Heterogenous mixture
c. Heterogeneous mixture
d. Homogeneous mixture

Check Your Progress

Answer these questions.
Question 1.
Name the process you would use to separate ammonium chloride and sodium chloride.
Answer:
Sublimation [Ammonium chloride sublimes on heating whereas sodium chloride (common salt) does not].

Question 2.
Name the process by which tea leaves are separated from prepared tea.
Answer:
Filteration

Question 3.
Name the process used to separate a mixture of two miscible liquids.
Answer:
Fractional distillation

Question 4.
What difference in the properties of oil and water enable their separation by using a separating funnel ?
Answer:
The oil is lighter and forms the upper layer while water is heavier and forms the lower layer in their mixture. The two liquids are immiscible.

A. Tick the most appropriate answer.

Question 1.
Which of the following is a pure substance ?
a. Soil
b. Honey
c. Water
d. Brass
Answer:
c. Water

Question 2.
Which of the following is a mixture ?
a. Common salt
b. Sea water
c. Carbon dioxide
d. Sulphur
Answer:
b. Sea water

Question 3.
Which of the following is a homogeneous mixture ?
a. Brass
b. Muddy water
c. Milk
d. Chalk powder in water
Answer:
a. Brass

Question 4.
Which of the following is a heterogeneous mixture ?
a. Dusty air
b. Sugar solution
c. Bronze
d. Blood
Answer:
a. Dusty air

Question 5.
The settling down of the insoluble heavy solid particles in a solid-liquid mixture is called
a. decantation
b. sieving
c. sedimentation
d. winnowing
Answer:
c. sedimentation

Question 6.
The process of adding alum to muddy water to help the suspended clay particles to settle down faster is called
a. loading
b. sedimentation
c. decantation
d. filtration
Answer:
a. loading

Question 7.
Common salt can be obtained from sea water by
a. evaporation
b. sublimation
c. centrifugation
d. filtration
Answer:
a. evaporation

Question 8.
Pure copper sulphate in the form of crystals can be obtained from its saturated solution by the process of –
a. evaporation
b. fractional distillation
c. centrifugation
d. crystallization
Answer:
d. crystallization

B. Fill in the blanks

Question 1.
A …………… substance has only one kind of particles.
Answer:
A pure substance has only one kind of particles.

Question 2.
An ………….. is a homogenous mixture of two or more metals, or metals and non-metals.
Answer:
An alloy is a homogenous mixture of two or more metals, or metals and non-metals.

Question 3.
Ammonium chloride can be separated from common salt by the process of …………..
Answer:
Ammonium chloride can be separated from common salt by the process of sublimation.

Question 4.
Alum is added to muddy water to hasten the process of ………….
Answer:
Alum is added to muddy water to hasten the process of sedimentation.

Question 5.
The insoluble solid left behind on the filter paper during filtration is called …………
Answer:
The insoluble solid left behind on the filter paper during filtration is called residue.

Question 6.
Cream is separated from milk by ………….
Answer:
Cream is separated from milk by centrifugation.

Question 7.
Pure water can be obtained from a solution of common salt by ………….
Answer:
Pure water can be obtained from a solution of common salt by evaporation.

Question 8.
A separating funnel is used to separate two …………… liquids.
Answer:
A separating funnel is used to separate two immiscible liquids.

C. State if the following statements are true or false. Correct the statement if it is false.

Question 1.
A mixture has a definite set of properties.
Answer:
False. A pure substance has a definite set of properties.

Question 2.
The constituents of a mixture can be separated by simple physical means.
Answer:
Tme

Question 3.
A heterogeneous mixture has a uniform composition throughout the mixture.
Answer:
False. A homogeneous mixture has a uniform composition throughout the mixture.

Question 4.
Sieving is a better method of separating bran and wheat flour than winnowing.
Answer:
Tme

Question 5.
Winnowing is based on the difference in the weights of the constituent particles.
Answer:
Time

Question 6.
We can get water from a mixture of salt and water by sedimentation.
Answer:
False. We can get water from a mixture of salt and water by evaporation.

Question 7.
Alcohol and water are immiscible liquids.
Answer:
False. Alcohol and water are miscible liquids.

D. Match the following.

1. Separating sawdust from water a. distillation
2. Separating iron fillings from sand b. sublimation
3. Separating sodium chloride from ammonium chloride c. innoing
4. Separating a mixture of common salt and water d. magnetic separation
5. Separating husk from grains e. filtration
f. evaporation

Answer:

1. Separating sawdust from water e. filtration
2. Separating iron fillings from sand d. magnetic separation
3. Separating sodium chloride from ammonium chloride d. magnetic separation
4. Separating a mixture of common salt and water f. evaporation
5. Separating husk from grains c. innoing

E. Answer the following in short.

Question 1.
What is a homogeneous mixture ?
Answer:
A mixture is said to be homogeneous if its constituents are uniformly mixed and it has the same properties throughout. Examples : Air, tap water, blood, brass, etc.

Question 2.
Why do oil and water form a heterogeneous mixture ?
Answer:
Oil and water are immiscible liquids (do not mix well and form separate layers upon standing) and do not have same properties throughout when mixed, hence oil and water form a heterogeneous mixture.

Question 3.
What is the principle of separation of mixtures ?
Answer:
The difference in the properties of the constituents of a mixture
form the basis or principle for separating them from each other. (Each constituent of a mixture has its own properties.)

Question 4.
Which property of the substance is used in separating.
a. husk from grain
Ansswer:
The difference in the weight of the constituent particles (husk and grain) – Principle for winnowing.

b. iodine from common salt ?
Answer:
Iodine sublimes on heating: Sublimation separates a mixture containing a constituent that sublimes.

Question 5.
Name a substance you will add to muddy water to speed up sedimentation.
Answer:
Alum

Question 6.
What type of mixtures are separated by filtration ?
Answer:
Solid-liquid mixture in which the solid is insoluble in the liquid.

Question 7.
What are immiscible liquids ? give an example.
Answer:
Liquids which do not mix with each other and form separate layers upon standing are called immiscible liquids. For example, kerosene oil and water.

F. Answer the following in detail.

Question 1.
What are mixtures ? Give three characteristics of mixtures.
Answer:
A mixture consists of molecules of two or more substances (elements, compounds or both) in any proportion such that they do not undergo chemical change. For example, air is a mixture of a number of gases such as oxygen, nitrogen and carbon dioxide.

Characteristics of mixtures :

  1. The constituents in a mixture may be present in any ratio or proportion.
  2. A mixture does not have any specific property of its own. In a mixture, each constituent exhibits its original properties.
  3. A mixture does not have a fixed melting or boiling point.
  4. The constituents of a mixture can be separated by simple physical means.

Question 2.
State the differences between homogeneous and heterogenous mixtures.
Answer:
Homogeneous mixture :

  1. It is a mixture in which the constituents are uniformly mixed.
  2. It has the same properties throughout.
  3. Examples : Sugar in water, air, tap water, blood, alloys like brass, bronze, common salt solution, etc.

Heterogeneous mixture :

  1. It is a mixture in which the constituents are not uniformly mixed.
  2. It does not have the same properties throughout.
  3. Examples: Chalk powder in water, muddy water, smoke, petrol and water, dusty air, suspensions, emulsions.

Question 3.
Define the following terms.
a. Sublimation
b. Filtration
c. Centrifugation
d. Crystallization
e. Distillation
Answer:
a. Sublimation – The change of a solid directly into its vapour state without passing through its liquid state is called sublimation.
b. Filtration – The process of separating the fine insoluble solid particles from a solid-liquid mixture through a filter is called filtration.
c. Centrifugation – Centrifugation is a method for separating the fine suspended solid particles from a solid-liquid mixture by rotating the mixture in a centrifuge.
d. Crystallization – Crystallization is the process of separating a pure solid in the form of its chrystals from its solution.
e. Distillation – Distillation is the process of separation of a liquid from its solution with a solid constituent by heating the liquid to its vapour form and then cooling the vapour to get back the pure liquid.

Question 4.
State the principles on which the following techniques of separation are based.
a. Handpicking
b. Winnowing
c. Filtration
d. Evaporation
e. Use of a separating funnel
Answer:
a. Principle of handpicking – This method is based on the difference in size, colour or shape of the constitutent particles.
b. Principle of Winnowing – This method is based on the difference in the weights of the constituent particles.
c. Principle of Filtration – This process is used for separating the constituents of a heterogeneous solid-liquid mixture in which the solid particles are lighter and insoluble in the liquid.
d. Principle of Evaporation – The liquid constituent of the mixture evaporates leaving behind the solid constituent,
e. Principle of use of a separating funnel – The method works when two liquids are immiscible. The heavier liquid forms the lower layer and the lighter liquid forms the upper layer.

Question 5.
State the technique of separation of immiscible liquids using a separating funnel.
Answer:
Technique of separation of immiscible liquids using a separating funnel- The mixture (for example, oil and water) is placed in a separating funnel. The mixture forms two clear layers after sometime – the lighter liquid (oil) forms the upper layer and the heavier liquid (water) forms the lower layer. When the stopper of the funnel is opened slowly, the heavier liquid (water) comes out first and is collected in a container. When
Living Science Chemistry Class 6 ICSE Solutions - 1
the lower layer is transferred or drained completely, the stopper of the funnel is closed. The lighter liquid (oil) remains in the separating funnel.

Question 6.
Example the solvent extraction method.
Answer:
Solvent extraction method is used when one constituent of a mixture is soluble in a particular liquid whereas the other constituent is insoluble in it. For example, sugar is soluble in water whereas sand is insoluble in water. To separate sugar from a mixture of sugar and sand, water is added to the mixture. The sugar gets dissolved in water. The solution is then filtered. The sand remains as a residue on the filter paper. The sugar solution is obtained as a filterate. This is then evaporated to get sugar.

G. Answer the following.

Question 1.
Air and tap water are mixtures. Give reasons.
Answer:
Air is a mixture as it is a mixture of number of gases like oxygen, nitrogen and carbon dioxide. Air has no characteristic property of its own but the components of air retain their individual properties.
Similarly, tap water is a mixture as it is a mixture of molecules of many elements and compounds present in any ratio or proportion. It does not have any specific property of its own and no fixed melting or boiling point.

Question 2.
How will you separate the constituents of a mixture containing iron filings, common salt and sand ?
Answer:
First will separate the iron filings using method of magnetic separation. Iron filings stick to the magnet and are removed. Then to separate common salt and sand, solvent extraction method is used. Water is added to the mixture of salt and sand. The salt gets dissolved in water. The solution is then filtered. The sand remains as a residue. The salt solution is obtained as a filterate. This is then evaporated to get salt.

H. Draw labelled diagrams of the following.

Question 1.
To show the separation of sawdust from water
Answer:
Living Science Chemistry Class 6 ICSE Solutions - 2

Question 2.
To show the recovery of w ater in the pure form from sea water.
Answer:
Living Science Chemistry Class 6 ICSE Solutions - 3

Living Science Chemistry Class 6 ICSE Solutions

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