Vidaara.orgClass 9 · Chemistry
CodeVID-C9-02-T2-01
Assignment — Separation of Mixtures
Name: ____________________
Roll No.: __________
Date: ____________
General Instructions
- All questions are compulsory.
- Section A carries 1 mark each, Section B 2 marks, Section C 3 marks and Section D 5 marks.
- Show all working for Sections B, C and D. Only final answers are given at the end — for full solutions, raise your doubts with your teacher.
Section A — Multiple Choice Questions
5 × 1 = 5 marks
1.
Cream is separated from milk by:
- A.filtration
- B.evaporation
- C.centrifugation
- D.sublimation
2.
Which of these substances sublimes?
- A.Common salt
- B.Ammonium chloride
- C.Sand
- D.Sugar
3.
Petroleum is refined into its components by:
- A.crystallisation
- B.fractional distillation
- C.a separating funnel
- D.chromatography
4.
To recover pure crystals of a soluble solid, the best method is:
- A.evaporation
- B.filtration
- C.crystallisation
- D.decantation
5.
The first gas to boil off when liquid air is warmed in a column is:
- A.oxygen
- B.argon
- C.carbon dioxide
- D.nitrogen
Section B — Short Answer (2 marks)
3 × 2 = 6 marks
6.
How is a separating funnel used to separate oil and water?
7.
Why can centrifugation separate particles that filtration cannot?
8.
State the principle of chromatography.
Section C — Short Answer (3 marks)
2 × 3 = 6 marks
9.
Distinguish between distillation and fractional distillation, giving one use of each.
10.
A mixture contains iron filings, sand, common salt and ammonium chloride. Outline the steps to separate all four.
Section D — Long Answer (5 marks)
1 × 5 = 5 marks
11.
Describe, with a labelled outline, how the gases of air are obtained from liquid air, and explain why fractional distillation (not simple distillation) is required.
Answer Key
Section A — Multiple Choice Questions
- (C) centrifugation
- (B) Ammonium chloride
- (B) fractional distillation
- (C) crystallisation
- (D) nitrogen
Section B — Short Answer (2 marks)
- The mixture is poured in and allowed to settle into two layers; the denser water is run off first through the stopcock, then the lighter oil is collected.
- Some suspended particles are too small to be trapped by filter paper; centrifugation spins them at high speed so the denser particles are forced to the bottom and the liquid stays on top.
- It separates components that dissolve in the same solvent but move through the medium at different rates, so each travels a different distance and forms a separate spot.
Section C — Short Answer (3 marks)
- Distillation separates miscible liquids whose boiling points differ by more than 25 C (e.g. acetone and water). Fractional distillation uses a fractionating column for liquids with close boiling points (e.g. separating the gases of air or refining petroleum).
- Use a magnet to remove iron filings; warm the rest so ammonium chloride sublimes and is collected; add water to dissolve the salt and filter out the insoluble sand; evaporate or crystallise the filtrate to recover the salt.
Section D — Long Answer (5 marks)
- Air is filtered to remove dust, then compressed and cooled until it liquefies. The liquid air is allowed to warm slowly inside a fractionating column. Because nitrogen, argon and oxygen have boiling points very close together (about -196 C, -186 C and -183 C), simple distillation cannot separate them. The packed column gives repeated evaporation and condensation, so each gas boils off in turn as the temperature rises — nitrogen first, then argon, then oxygen — and is drawn off separately. The boiling-point difference being so small is exactly why the column of fractional distillation is essential.
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