Exploring Mixtures and their Separation — Practice

Question 1

Is air a homogeneous or heterogeneous mixture?

Accepted Answer

Air is a homogeneous mixture of gases (uniform composition).

✦ Answer: homogeneous.

Question 2

In a sugar solution, name the solute and the solvent.

Accepted Answer

Solute = sugar (dissolved); solvent = water (dissolving medium).

✦ Answer: sugar (solute), water (solvent).

Question 3

Which method separates sand from water?

Accepted Answer

Sand is insoluble, so use filtration.

✦ Answer: Filtration.

Question 4

5 g of salt is dissolved in 45 g of water. Find the mass % of salt.

Accepted Answer

Step 1 — mass of solution = 5 + 45 = 50 g.

Step 2 — mass % = (5/50) × 100 = 10%.

✦ Answer: 10%.

Question 5

Why is a beam of light visible when it passes through fog but not through clear air?

Accepted Answer

Step 1 — Fog is a colloid; its particles (1–1000 nm) scatter light — the Tyndall effect — making the beam visible.

Step 2 — Clear air is essentially a true solution of gases with particles too small to scatter visible light.

✦ Answer: colloidal fog scatters light (Tyndall); clear air does not.

Question 6

Give two differences between a true solution and a suspension.

Accepted Answer

1) Particle size: true solution < 1 nm; suspension > 1000 nm.

2) Stability: a true solution never settles; a suspension settles on standing and can be filtered.

✦ Answer: particle size and settling/stability.

Question 7

How would you separate a mixture of salt, sand and iron filings?

Accepted Answer

Step 1 — Use a magnet to remove the iron filings.

Step 2 — Add water and stir: salt dissolves, sand does not. Filter — sand stays on the filter paper.

Step 3 — Evaporate the filtrate (salt water) to recover the salt.

✦ Answer: magnet → dissolve + filter → evaporate.

Question 8

Why is distillation, not simple evaporation, used to obtain pure water from sea water?

Accepted Answer

Step 1 — Evaporation would lose the water as vapour and leave only the salts.

Step 2 — Distillation boils the sea water AND condenses the steam back to liquid, collecting pure water while salts stay behind.

✦ Answer: distillation recovers the water (by condensing the vapour); evaporation does not.

Practice — Exploring Mixtures and their Separation