Answers · Mixtures and separation

Mixtures and separation — return questions key

Check meaning, not exact wording. These are teaching points, not official Cambridge marks.

1. R01 · Return

Model answer. Ethanol is the solvent because benzoic acid is the substance that has dissolved in it.

A full answer includes

I identified ethanol as the solvent.
I used the fact that benzoic acid dissolves in ethanol as the reason.

Also accept

Liquid ethanol is the dissolving medium in the stated case.

Watch for

“Benzoic acid is the solvent because its name appears first.” — Sentence order doesn’t set the roles. Follow what dissolved in what.

2. R04 · Return

Model answer. The solid is the evaporation residue because it remains after the water is removed. Residue is not restricted to filtration, so paper is not necessary.

A full answer includes

The solid left after evaporation is a residue.
The term is not restricted to material on filter paper.

Also accept

Material remaining in the basin is residue after evaporation.

Watch for

“Only sand left on paper can be residue.” — Residue describes what remains after a separation, not one material or apparatus.

3. R06 · Return

Model answer. Choose A. N remains undissolved and is retained; O dissolves and passes with A in the filtrate. B and C leave the two solids together in one product.

A full answer includes

I chose A because only O dissolves.
N remains as residue; O is dissolved in A in the filtrate.

Also accept

Selective dissolution in A separates retained N from solution of O.

Watch for

“Choose B because both dissolve completely.” — That would leave both in the filtrate, so the proposed filtration doesn’t separate them.

4. R02 · Return

Model answer. Sugar is the solute. It is dispersed through the water and remains present, so the sample contains sugar and water instead of water alone.

A full answer includes

I identified sugar as the solute.
I stated that dissolved sugar remains present even when crystals are not visible.
I named both sugar and water as components.

Also accept

The sugar has dissolved, not been destroyed; both components remain.

Watch for

“It must be water alone because it is clear.” — A clear appearance doesn’t remove the sugar that the question states is dissolved.

5. R07 · Return

Model answer. The filtration did not retain all the grains. Torn paper, bypass around the paper or particles able to pass through it are possible causes; any two are acceptable. The observation doesn’t prove dissolution and doesn’t identify a single fault by itself.

A full answer includes

Some undissolved grains reached the receiver, so separation was incomplete.
I offered two plausible causes, such as torn/bypassed paper or grains too fine for the stated paper.
Visible grains do not prove dissolution; the data do not identify a unique fault.

Also accept

Incomplete removal of visible solid is established; the exact cause needs further checking.

Watch for

“The grains must have dissolved because they reached the receiver.” — Visible grains are still a separate solid. They may have passed through or around a defective/unsuitable filter.

6. R03 · Return

Model answer. The iodine in ethanol forms a homogeneous solution because it is dissolved uniformly throughout. Oil and water form a heterogeneous mixture because they remain in separate layers with different compositions. The unknown clear liquid could be pure or could contain dissolved solute; clarity alone can’t decide.

A full answer includes

The first is a homogeneous solution: dissolved iodine is mixed uniformly throughout ethanol.
The second is heterogeneous: the oil and water remain in separate liquid layers of different composition.
The third cannot be classified as pure from clarity alone.

Also accept

Bottle1 is homogeneous; Bottle2 is heterogeneous. Bottle3 needs evidence about its contents before a purity claim.

Watch for

“Both are definitely solutions because both are liquids.” — Being liquid doesn’t establish that two or more substances are present or dissolved.
“Two transparent layers make one homogeneous solution.” — Transparency describes appearance. Separate oil and water layers have different compositions, so the whole sample is heterogeneous.

7. R05 · Return

Model answer. The filtrate is H dissolved in water, collected after passing through the paper. J remained as the residue, so it is not a component of the stated ideal filtrate.

A full answer includes

Filtrate is the solution of H in water that passed through.
J is excluded because the stated filter retained it.

Also accept

Water and dissolved H comprise the collected solution.

Watch for

“H is excluded because it is called a solid.” — H is explicitly dissolved. Distinguish its identity from its current dispersed state.

8. R08 · Return

Model answer. Collect A with the magnet while the mixture is dry. Add water to dissolve B; filter to collect C on paper and solution of B in the receiver. Remove water from that separate filtrate by the approved procedure to leave B in its basin. Each step uses the stated property and retains separate products.

A full answer includes

Collect A magnetically from dry powder.
Dissolve B in water; filter C as residue and collect B solution.
Remove water from separate filtrate to recover B; explains selective attraction/solubility/retention/stability.

Also accept

Three collected solids are accounted for with justified steps and the dry-only condition respected.

Watch for

“The magnet can be left until after adding water despite the supplied use restriction.” — This case specifies dry-powder magnetic collection. A plan must respect that condition instead of assuming another capability.