Class 9 Science

# Mixture

## NCERT Exemplar Problem

#### Part 2

Question 33: Fractional distillation is suitable for separation of miscible liquids with a boiling point difference of about 25 K or less. What part of fractional distillation apparatus makes it efficient and possess an advantage over a simple distillation process. Explain using a diagram.

Answer: Apparatus used for fractional distillation has a fractionating column. A simple fractionating column has glass beads in it which provide additional surface area because of which the vapours can spread and cool rapidly.

Ref: NCERT Book

Hence, fractionating column is used to provide the additional surface and to facilitate the cooling of vapour in many cycles.

Question 34: (a) Under which category of mixtures will you classify alloys and why?

Answer: When constituent particles of a combination of two or more element or compound retains their properties, then it is called mixture. In an alloy the constituent particles, hence alloys are classified as mixture. For example; steel is an alloy of carbon and iron.

(b) A solution is always a liquid. Comment.

Answer: Since, a solution is the homogeneous mixture of two or more substances, thus it is not necessary that a solution would always a liquid.

A solution can be in all the three states of matter. A solution is a homogeneous mixture and can be in all the three states of matter.

Examples:

• Solution of alcohol in water is a liquid.
• Air is a solution of different gas.
• Alloy is a solution which is in the form of solid.

(c) Can a solution be heterogeneous?

Answer: Solution is defined as the homogeneous mixture, hence a solution cannot be heterogeneous. But when a mixture becomes heterogeneous, it cannot be fall under the definition of solution.

Question 35: Iron filings and sulphur were mixed together and divided into two parts, "A" and "B". Part A was heated strongly while Part B was not heated. Dilute hydrochloric acid was added to both the Parts and evolution of gas was seen in both the cases. How will you identify the gases evolved?

Answer: Hydrogen gas is released, when dilute hydrochloric acid is added to part A. Hydrogen gas can be tested by brining a burning matchstick or candle near it. When a burning matchstick is placed near the hydrogen gas, it burns with a pop sound, which is a test for hydrogen gas.

Hydrogen sulphide gas released when dilute hydrochloric acid was added to part B. Hydrgoen sulphide gas smells like a rotten egg, hence it could be confirmed by its smell.

Question 36: A child wanted to separate the mixture of dyes constituting a sample of in36. A child wanted to separate the mixture of dyes constituting a sample of ink. He marked a line by the ink on the filter paper and placed the filter paper in a glass containing water as shown in Fig. The filter paper was removed when the water moved near the top of the filter paper.

(i) What would you expect to see, if the ink contains three different coloured components?

Answer: Streaks of different colours can be seen on the filter paper.

(ii) Name the technique used by the child.