Is matter around us pure Worksheet-8

Is matter around us pure Worksheet-8

21. What will happen if a colloidal solution of sulphur is centrifuged in a centrifugal machine for sometime?

A. Yellow coloured sulphur will float at the surface of solution

B. Sulphur will dissolve completely forming true solution

C. Yellow ppt of sulphur will be formed and supernatant solution will be colourless

D. The solution will become dark yellow in colour due to dissolution of more sulphur in it

22. Rusting of iron is a ______change.

A. Chemical

B. Physical

C. Reversible

23. What might have happened if nitrogen was absent in air?

A. There would have been no plants as atmospheric nitrogen is fixed by microorganisms and used by plants

B. Combustion once started would never stop

C. No effect as we inhale oxygen and not nitrogen

D. Oxides of nitrogen which are pollutants would not have been formed

24. What is the unit of mass percent ?

A. No unit          B. g/L                 C. Kg /L             D. mg/ml

25. What is the nature the solution formed by mixing mustard oil and water ?

A. Colloidal solution

B. Emulsion

C. Gel

D. Both are immiscible liquids

26. Which among the following is colloidal solution in which solid acts as the dispersed phase and gas as the dispersion medium?

A. Bread             B. Butter            C. Smoke           D. Boot polish

27. The two compounds which sublime on heating are_____.

A. Sodium chloride and iodine crystals

B. Potassium chloride and iodine crystals

C. Ammonium chloride and iodine crystals

D. Lithium chloride and camphor

28. You are provided with a mixture of carbon tetrachloride and water. The constituents can be separated by_____.

A. Fractional distillation

B. Sublimation as carbon tetrachloride sublimes

C. Separating funnel

D. Steam distillation

29. Can a mixture of alcohol and water be separated with the help of a separating funnel ?

A. No                  B. Yes                 C. Can’t say

30. Sodium chloride contains two elements, but it is still a pure substance because_____

A. Elements cannot be separated by physical methods of separation

B. It has a sharp melting point

C. Sodium chloride is formed by the chemical combination of sodium and chlorine

D. All of these

31. What types of mixtures are represented by the following?

(a) Carbon dioxide gas dissolved in water.

(b) Air containing suspended particles.

(c) Soap bubbles formed by blowing air into soap solution.

A. (a) Homogeneous (b) Heterogeneous (c) Heterogeneous

B. (a)Homogeneous (b) Homogeneous (c) Heterogeneous

C. (a) Heterogeneous (b) Homogeneous (c) Heterogeneous

D. (a) Heterogeneous (b) Heterogeneous (c) Heterogeneous

32. Two miscible liquids A and B are present in a solution. The boiling point of A is 60°C while that of B is 90°C. The method used for their separation is______.

A. Simple distillation

B. Fractional distillation

C. Steam distillation

33. Explain why water is a compound and not a mixture.

A. Hydrogen and oxygen combine in fixed ratio by mass in water

B. Water is a liquid whereas oxygen and hydrogen are gases

C. Oxygen supports combustion where as water is used as fire extinguisher

D. Properties of water are different from its constituents

E. All of these

Answer Key:

21. C

Explanation: The yellow precipitate of sulphur will settle at the bottom of the tube and the solution collected above the precipitate will be colourless.

22. A

Explanation: The rust is a brown chemical compound known as hydrated ferric oxide (Fe₂O₃xH₂O). Iron undergoes chemical change.

23. B

Explanation: The role of nitrogen in air is to dilute the combustion effect of oxygen since nitrogen does not support combustion. Had nitrogen been absent, the combustion once started would never stop. You can well imagine as to what might have happened to us.

24. A

Explanation: Mass percent has no units as it is simply a ratio.

25. D

Explanation: Mustard oil and water are immiscible liquids. They can form emulsion in the presence of emulsifiers.

26. C

Explanation: Smoke, dust storm, haze are the colloidal solution in which solid particles are dispersed in air.

27. C

Explanation: Ammonium chloride and iodine crystals.

28. C

Explanation: Both are immiscible liquids. The separation can be done by the use of a separating funnel.

29. A

Explanation: No, it is not possible because alcohol (ethyl alcohol) and water are miscible. Separating funnel is used for separating immiscible liquids

30. D

Explanation: The two elements sodium and chlorine have combined with each other by chemical reaction to form sodium chloride (NaCl) which is a chemical compound. Since these elements cannot be separated from each other by any physical processes of separation, sodium chloride is a pure substance.

31. A

Explanation: (a) homogeneous (b) heterogeneous (c) heterogeneous

32. A

Explanation: The separation can be done by the process of simple distillation. The vapours of the liquid A will be formed at the temperature of 60°C. They will pass through the condenser and will collect as distillate. The liquid B with higher boiling point will remain in the flask.

33. E

Explanation: The properties of water are different from its constituents. Water has fire extinguishing property where as oxygen supports combustion. Hydrogen and oxygen are gases whereas water is a liquid. Hydrogen and oxygen combine in fixed ratio by mass.