Chemistry ICSE Class 6 Important Questions Chapter 4 Pure Substances and Mixtures
Practice Questions
Question 1.
Mention characteristics of pure substances.
Answer:
Characteristics of pure substances :
- A pure substance has a definite composition.
- It has a definite set of properties.
- It has fixed melting and boiling points.
- A pure substance cannot be separated into its components by physical means.
Question 2.
What is a solution, solute and solvent ?
Answer:
A solution is one in which one constituent dissolves in another constituent. The substance which dissolves in solvent is known as solute and the substance in which the solute dissolves is known as solvent. Example: In a solution of sugar and water, sugar is the solute and water is the solvent.
Question 3.
Define –
1. suspension
2. emulsion
Answer:
1. A suspension is a heterogeneous mixture in which small solid particles are suspended in a liquid.
Example : Chalk powder dissolved in water.
2. An emulsion is a heterogeneous mixture that consists of particles of one liquid dispersed (not dissolved) in another liquid. Example: milk.
Question 4.
State differences between compounds and mixtures.
Answer:
Compounds :
- A compound is a pure substance.
- A compound consists of two or moe elements combined together chemically
- Compounds are always homogeneous.
- A compound has a definite composition.
- In a compound, the constituents lose their identities, that is, a compound does not show the characteristics of its constituents elements.
- In the formation of a compound, energy in the form of heat, light, etc. is either absorbed or evolved.
- In a compound, the constituents can only be separated by chemical means.
- A compound has fixed melting and boiling points.
Mixtures :
- A mixture is an impure substance.
- A mixture consists of two or more substances (elements, compounds or both) which are not combined chemically)
- A mixture may be homo¬geneous or heterogenous.
- A mixture has variable composition, that is, the constituents of a mixture can be present in any ratio or proportion.
- In a mixture, the constituents do not lose their identity, that is, a mixture retains the chara¬cteristics of its constituents.
- The formation of a mixture does not involve any change in energy.
- The constituents of a mixture can be separated by simple physical means.
- A mixture does not have a fixed melting or boiling point.
Question 5.
What is the need for separation of mixtures ?
Answer:
- To remove a harmful or undesirable component.
- To obtain a useful substance.
- To obtain the pure sample of a substance.
Question 6.
Name few methods to separate solid-solid mixtures.
Answer:
Handpicking, sieving, winnowing, magnetic separation, sublimation.
Question 7.
Give one word for :
1. The method of separating undesirable constituents from a mixture by picking with hand.
Answer:
Handpicking
2. The method of separating undesirable constituents from a mixture by using a sieve.
Answer:
Sieving
3. The method of separating undesirable constituents from a mixture by using wind.
Answer:
Winnowing
4. The method of separating magnetic constituents from a mixture.
Answer:
Magnetic separation
5. The method of separating mixture of miscible liquids by distillation.
Answer:
Fractional distillation
6. The settling down of the insoluble heavy solid particles in a solid-liquid mixture at the bottom of the container.
Answer:
Sedimentation
7. The process of pouring the clear supernatant liquid without disturbing the sediment.
Answer:
Decantation
Question 8.
Name the process used to separate the following mixtures:
1. Stones from rice
Answer:
Handpicking .
2. Grains from chaff
Answer:
Winnowing
3. Iodine and common salt
Answer:
Sublimation
4. Sand in water/muddy water
Answer:
Sedimentation and decantation
5. Chalk powder in water
Answer:
Filteration
6. To separate blood cells from blood
Answer:
Centrifugation
7. To obtain pure/distilled water from tap water
Answer:
Distillation
8. Petrol and water
Answer:
Using separating funnel
Question 9.
Write the principle and two applications of centrifugation.
Answer:
Principle – When the mixture is rotated at a high speed, the lighter particles stay on the surface of the liquid while the heavier particles settle at the bottom of the container. Applications of centrifugation –
- The technique is used in dairies and homes to separate cream from milk.
- In washing machines, it is used to squeeze out water from wet clothes.
Question 10.
Name few methods to separate solid-liquid mixtures when
1. the solid is insoluble in the liquid.
Answer:
Sedimentation and decantation, filteration, centrifugation, loading.
2. the solid is soluble in the liquid.
Answer:
Evaporation, crystallization, distillation.
Question 11.
Why crystallization is a better technique, than evaporation ?
Answer:
Crystallization is a better technique than evaporation because of the following reasons.
- Some solids like sugar decompose or get charred on heating to dryness during evaporation.
- The soluble impurities do not get removed in the process of evaporation.
Question 12.
Fill in the blanks
1. A …………… substance consists of particles of only one kind.
Answer:
A pure substance consists of particles of only one kind.
2. Elements are made up of the same kind of …………..
Answer:
Elements are made up of the same kind of atoms.
3. Compounds are made up of the same kind of ……………
Answer:
Compounds are made up of the same kind of molecules.
4. Each substance in a mixture is called a …………… of the mixture.
Answer:
Each substance in a mixture is called a constituent of the mixture.
5. A ………….. substance is always homogeneous.
Answer:
A pure substance is always homogeneous.
6. A homogeneous solid mixture of two or more metals or metals and non-metals is called …………..
Answer:
A homogeneous solid mixture of two or more metals or metals and non-metals is called an alloy.
7. Chalk powder dissolved in water forms a …………..
Answer:
Chalk powder dissolved in water forms a suspension.
8. Milk is a …………… mixture and called an
Answer:
Milk is a heterogeneous mixture and called an emulsion.
9. Petroleum or crude oil is separated into groups of compounds by a process called an …………..
Answer:
Petroleum or crude oil is separated into groups of compounds by a process called an refining.
10. During sedimentation, the solid particles that settle down in a layer at the bottom of the container are called the The clear liquid above the sediment is called the ……………
Answer:
During sedimentation, the solid particles that settle down in a layer at the bottom of the container are called the sediment.
The clear liquid above the sediment is called the supernatant.
11. During Alteration, the solid left on the filter is called the …………… and the clear liquid which passes through the filter is called the …………….
Answer:
During Alteration, the solid left on the filter is called the residue and the clear liquid which passes through the filter is called the filtrate.
12. ………….. are solids with regular shapes, flat surface and straight edges.
Answer:
Crystals are solids with regular shapes, flat surface and straight edges.
13. Common salt obtained from sea water is purified by the process of …………..
Answer:
Common salt obtained from sea water is purified by the process of crystallization.
14. Fractional distillation works on the basis of the difference in the ………….. of liquids.
Answer:
Fractional distillation works on the basis of the difference in the boiling points of liquids.
ICSE Class 6 Chemistry Important Questions