Vidaara.orgClass 9 · Chemistry
CodeC9-CHEM-2-CW
Is Matter Around Us Pure — Chapter Assignment
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 the numerical questions.
Section A (1 mark each)
6 × 1 = 6 marks
1.
Which is a heterogeneous mixture?
- A.Salt solution
- B.Air
- C.Sand and iron filings
- D.Brass
2.
The Tyndall effect is observed in a:
- A.true solution
- B.colloid
- C.compound
- D.element
3.
Which method separates a soluble solid from its solution?
- A.A separating funnel
- B.Evaporation
- C.Sublimation
- D.Magnetic separation
4.
Rusting of iron is an example of a:
- A.physical change
- B.chemical change
- C.change of state
- D.sublimation
5.
Water is an example of a:
- A.mixture
- B.compound
- C.element
- D.colloid
6.
Solubility is usually expressed as grams of solute per:
- A.10 g solvent
- B.50 g solvent
- C.100 g solvent
- D.1 g solvent
Section B (2 marks)
4 × 2 = 8 marks
7.
Distinguish between a solute and a solvent with an example.
8.
18 g of glucose is dissolved in 82 g of water. Find the mass percentage of glucose.
9.
State two differences between a physical and a chemical change.
10.
Name the method to separate (a) oil from water and (b) ammonium chloride from salt.
Section C (3 marks)
3 × 3 = 9 marks
11.
Compare a true solution, a colloid and a suspension on particle size, settling and the Tyndall effect.
12.
How much copper sulphate and water are needed to make 300 g of a 6% (by mass) solution?
13.
Distinguish between metals, non-metals and metalloids with one example each.
Section D (5 marks)
2 × 5 = 10 marks
14.
A mixture contains common salt, sand, iron filings and ammonium chloride. Describe, step by step, how you would obtain each component in pure form, naming the method and principle used at each stage.
15.
Explain the iron and sulphur experiment and use it to bring out three differences between a mixture and a compound.
Answer Key
Section A (1 mark each)
- (C) Sand and iron filings
- (B) colloid
- (B) Evaporation
- (B) chemical change
- (B) compound
- (C) 100 g solvent
Section B (2 marks)
- The solvent is the larger component that does the dissolving (e.g. water); the solute is the smaller, dissolved component (e.g. salt).
- Mass of solution = 18 + 82 = 100 g; mass % = (18 / 100) x 100 = 18%.
- A physical change forms no new substance and is usually reversible; a chemical change forms a new substance and is hard to reverse.
- (a) A separating funnel; (b) sublimation.
Section C (3 marks)
- True solution: < 1 nm, do not settle, no Tyndall effect. Colloid: 1-100 nm, do not settle, shows Tyndall effect. Suspension: > 100 nm, settle on standing, scatter light.
- Copper sulphate = (6 / 100) x 300 = 18 g; water = 300 - 18 = 282 g.
- Metals: lustrous, good conductors, malleable (copper). Non-metals: dull, brittle, poor conductors (sulphur). Metalloids: in-between properties (silicon).
Section D (5 marks)
- First run a magnet through the mixture to pull out the iron filings (magnetic separation). Next warm the remainder gently so ammonium chloride sublimes and re-deposits on a cool surface, leaving salt and sand (sublimation). Add water and stir to dissolve the salt; filter to retain the insoluble sand on the paper (filtration). Finally evaporate or crystallise the filtrate to recover pure salt (evaporation/crystallisation). Each step uses a single physical property — magnetism, sublimation, solubility difference and boiling away the solvent.
- When iron filings and sulphur are merely mixed, a magnet pulls out the iron, the yellow sulphur is still visible, and each keeps its own properties — a mixture. On strong heating, a black solid iron sulphide (FeS) forms; a magnet no longer attracts it and dilute acid gives a foul-smelling gas, showing a new substance. Three differences: (1) composition — a mixture has a variable ratio, a compound a fixed ratio by mass; (2) properties — a mixture keeps its components' properties, a compound has new ones; (3) separation — a mixture is separable physically (here by a magnet), a compound only chemically.
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