Class 9 Science Chapter 2 Case Based Questions - Is Matter Around Us Pure??

(I) Read the given passage and answer the questions that follow based on the passage and related studied concepts.
A pure substance consist of single type of particles. Mixture consist of more than one kind of pure form of matter. Mixtures can be separated by physical methods but pure substances especially compounds cannot be separated into chemical constituents by physical methods. Pure substance has same composition throughout. Soil and soft drinks are mixtures. Mixtures can be separated by various methods depending upon nature of substance present in it. Solution is a homogeneous mixture.

Q1: Name the process by which pure NaCl can be obtained from salt solution.
Ans: Crystallisation

Q2: What are alloys-compounds or mixtures?
Ans: Alloys are homogeneous mixtures of two or more metals or a metal and a non-metal e.g. Brass is alloy of Cu and Zn

Q3: What is size of particles in solution?
Ans: The size of particles in solutions are less than 1nm (10^–9m).

Q4: What is solute and solvent in cold drinks?
Ans: CO₂ gas, sugar, preservative are solute and water is solvent in cold drinks.

(II) Study the table showing melting points and boiling points of certain compounds. Answer the questions based on the table and related studied concepts
Q1: Which one of the given substances may be separated by using a water condenser?
Ans: Pentane; because temperature of water condenser is 25°C and boiling point of pentane is 36°C.

Q2: How can gases be separated that are present in air?
Ans: By fractional distillation of liquid air.

Q3: If sample of urea has melting point 129°C, then:
(a) It is impure
(b) It is pure
(c) It can not be predicted
(d) The compound is not urea
Ans: (a) It is impure

Q4: Which of the following will have boiling point 100°C?
(a) Distilled water
(b) Sea water
(c) River water
(d) Well water
Ans: (a) Distilled water will have boiling point 100°C.