ICSE Living Science Chemistry for Class 8 Solutions Chapter 3 Elements, Compounds and Mixtures
Check Your Progress (Page 22)
Fill in the blanks.
Question 1.
Elements are represented by …………
Answer:
Elements are represented by symbols.
Question 2.
The symbol of sodium is …………
Answer:
The symbol of sodium is Na.
Question 3.
The elements present in common salt are ………… and
Answer:
The elements present in common salt are sodium and chlorine.
Question 4.
A ………… is a substance made up of two or more elements.
Answer:
A compound is a substance made up of two or more elements.
Question 5.
The properties of a compound are different from those of its constituent …………
Answer:
The properties of a compound are different from those of its constituent elements.
Think And Answer (Page 23)
A pure substance is always homogeneous. Do you agree?
Answer:
A pure substance is always homogeneous. Yes. It is true.
Check Your Progress (Page 31)
Answer these questions.
Question 1.
Name the processes you would use to separate a mixture of calcium carbonate and common salt.
Answer:
Filtration followed by evaporation.
Question 2.
Name the process by which sand is separated from its mixture in water.
Answer
Sedimentation and decantation.
Question 3.
Name the process used to separate a mixture of two miscible liquids.
Answer:
Fractional distillation.
Question 4.
Oil and water can be separated by using a separating funnel. What differences in their properties make this possible?
Answer:
The method works when two liquids are immiscible. The heavier liquid forms the lower layer and the lighter liquid forms the upper layer.
A. Tick the most appropriate answer
1. What is the symbol of iron?
a. I
b. Fe
c. In
d. Na
Answer :
b. Fe
Question 2.
Which of the following is a homogeneous mixture?
a. brass
b. muddy water
c. milk
d. chalk powder in water
Answer:
a. brass
Question 3.
What is the settling down of the insoluble heavy solid particles in a solid-liquid mixture called?
a. decantation
b. sieving
c. sedimentation
d. winnowing
Answer;
c. sedimentation
Question 4.
Which process can be used to obtain common salt from sea water?
a. evaporation
b. sublimation
c. sedimentation
d. filtration
Answer:
a. evaporation
Question 5.
Which of the following is used to obtain pure copper sulphate in the form of crystals from its saturated solution?
a. evaporation
b. fractional distillation
c. distillation
d. crystallization
Answer:
d. crystallization
Question 6.
Which of the following processes works on the basis of the difference in the boiling points of liquids?
a. sedimentation
b. filtration
c. decantation
d. fractional distillation
Answer:
d. fractional distillation
Question 7.
Which of the following is used to separate oil from water?
a. evaporation
b. filtration
c. separating funnel
d. distillation
Answer:
c. separating funnel
Question 8.
Which of the following is used to separate complex mixtures like coloured dyes from ink?
a. evaporation
b. chromatography
c. separating funnel
d. distillation
Answer:
b. chromatography
B. Fill in the blanks.
Question 1.
The …………. of an element is the abbreviation of its full name.
Answer:
The symbol of an element is the abbreviation of its full name.
Question 2.
Natrium is the Latin name of ………….
Answer:
Natrium is the Latin name of sodium.
Question 3.
A …………. is always made up of the same elements combined in a fixed ratio.
Answer:
A compound is always made up of the same elements combined in a fixed ratio.
Question 4.
The number of atoms present in a molecule of an element is called its ………….
Answer:
The number of atoms present in a molecule of an element is called its atomicity.
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.
Miscible liquids are separated by the process of …………. distillation.
Answer:
Miscible liquids are separated by the proces of fractional distillation.
Question 7.
A separating funnel is used to separate two …………. liquids.
Answer:
A separating funnel is used to separate two immiscible liquids.
C. Write true or false. Correct the false statements
Question 1.
The IUPAC approves the names and symbols of new elements.
Answer:
True
Question 2.
A compound is made up of one element.
Answer:
False; A compound is made up of two or more elements chemically combined in a fixed ratio.
Question 3.
The properties of a compound are different from those of its constituent elements.
Answer:
True
Question 4.
A mixture has a fixed melting or boiling point
Answer:
False; A mixture does not have a fixed melting or boiling point.
Question 5.
The constituents of a mixture can be separated by simple physical means.
Answer:
True
Question 6.
The separation of a mixture of liquids by distillation is called fractional distillation.
Answer:
True
Question 7.
Miscible liquids are separated by using a separating funnel.
Answer:
False; Immiscible liquids are separated by using a separating funnel.
D. Match the columns
| 1. Separating kerosene from water | a. fractional distillation |
| 2. Separating alcohol from water | b. evaporation |
| 3. Separating chalk powder from water | c. separating funnel |
| 4. Separating camphor from common salt | d. magnetic separation |
| 5. Separating common salt from sea water | e. filtration |
| f. sublimation |
Answer:
| 1. Separating kerosene from water | c. separating funnel |
| 2. Separating alcohol from water | a. fractional distillation |
| 3. Separating chalk powder from water | e. filtration |
| 4. Separating camphor from common salt | f. sublimation |
| 5. Separating common salt from sea water | b. evaporation |
E. Answer the following in short
Question 1.
What is a compound?
Answer:
A compound is a substance made up of two or more elements. The elements in a compound are chemically combined in a fixed ratio.
Question 2.
What is an alloy ?
Answer:
A homogeneous solid mixture of two or more metals or metals and non-metals is called an alloy.
Question 3.
Name the methods of separation of the components of solid- solid mixtures.
Answer:
The methods of separation of the components of solid-solid mixture are: handpicking, sieving, winnowing and magnetic separation.
Question 4.
What is sublimation?
Answer:
The change of a solid directly into its vapour state without passing through the liquid state is called sublimation.
Question 5.
What is loading?
Answer:
During sedimentation, the heavier coarse particles settle down quickly. But the finer particles settle down very slowly. So, the finer particles are made to settle down faster by adding a certain chemical. This process is called loading.
Question 6.
Differentiate between residue and filtrate.
Answer:
The mixture is allowed to pass through a filter with pores that allow the liquid to pass through but not the solid particles. The solid left on the filter is called the residue and the clear liquid that passes through the filter is called the filtrate.
Question 7.
What is fractional distillation?
Answer:
The separation of a mixture of liquids by distillation is called fractional distillation.
F. Answer the following in detail
Question 1.
State the characteristics of a compound.
Answer:
(i) A compound is made up two or more elements.
(ii) A compound is always made up of the same elements combined in a fixed ratio.
(iii) A compound is always homogeneous, that is, all samples of a compound are identical in composition and have the same properties throughout.
(iv) The properties of a compound are different from those of its constituent elements.
(v) Energy is usually given off or absorbed when a compound is formed.
Question 2.
Differentiate between elements and compounds.
Answer:
Element :
- An element is made up of only one kind of substance.
- An element cannot be broken down into simpler substances by chemical means.
- An element has its own set of properties.
- The molecules of an element are formed by the combination of two or more atoms of the same element.
Compound :
- A compound is made up of two or more elements.
- A compound can be broken down into its constituent elements by chemical means.
- The properties of a compound are different from those of its constituent elements.
- When the atoms of two or more elements combine, they form a molecule of a compound.
Question 3.
Differentiate between suspension and emulsion with the help of examples.
Answer:
A suspension is a heterogeneous mixture in which small solid particles are suspended in a liquid. For example, chalk powder in water, some medicines and syrups are suspensions. An emulsion is a heterogeneous mixture that consists of particles of one liquid dispersed (not dissolved) in another liquid. For example, milk is an emulsion.
Question 4.
State the characteristics of mixtures.
Answer:
- The constituents in a mixture may be present in any ratio or proportion.
- A mixture does not have any specific property of its own.
- In a mixture, each constituent exhibits its original properties.
- The constituent of a mixture can be separated by simple physical means.
Question 5.
State the principle of fractional distillation.
Answer:
Principle of fractional distillation works on the basis of the difference in the boiling points of liquids. The mixture (for example, alcohol and water) is kept in a distillation flask and heated. The liquid with the lower boiling point (here, alcohol) evaporates first, gets condensed in the condenser and is collected in a flask. The liquid with the higher boiling point (water) remains in the distillation flask.
G. Draw a labelled diagram of the following
Separation of kerosene from water using a separating funnel
Answer:
Think And Answer
Question 1.
Air and tap water are mixtures. Explain.
Answer:
Air is mixture :
The constituents in air may be present in any ratio or proportion.
In air each constituent exhibits its original properties.
The constituents of air can be separated by simple physical means.
Tap water is a mixture :
Because it contains dissolved gases and minerals.
Question 2.
Oil and water form a heterogeneous mixture. Why?
Answer:
Oil and water form a heterogeneous mixture because they does
have uniform constituents and properties throughout.
Question 3.
Alum increases the rate of sedimentation. Why?
Answer:
Alum dissolves in water and makes the clay particles heavier and increases the rate of sedimentation.
Living Science Chemistry Class 8 ICSE Solutions