Can any more dissolve? — answer key

1. CQ1 · Practice

Model answer. No. It could dissolve more of the solute at that temperature.

A full answer includes

• I said it was unsaturated before the added crystal.
• I used its ability to dissolve more at that temperature as evidence.

Watch for

• “A clear solution must be unsaturated.” — Clear means transparent; it doesn’t tell us whether any more can dissolve.

2. CQ3 · Practice

Model answer. Choose the first and third statements: Concentrated describes relatively much solute per amount of solution. Saturated states that no more of that solute can dissolve at the specified temperature. Colour alone doesn’t establish either limit.

A full answer includes

• I selected the first and third statements.
• I distinguished relative solute amount from a dissolving limit at stated temperature.
• I said colour alone does not establish saturation.

Also accept

• Choose the first and third statements: Concentrated describes relatively much solute per amount of solution. Saturated states that no more of that solute can dissolve at the specified temperature. Colour alone does not establish either limit.

Watch for

• “A dark solution must be saturated.” — A dark solution may still dissolve more solute. Test it at a fixed temperature.

3. CQ2 · Practice

Model answer. No. Add a little of the same solute, stir and allow time at the same temperature. Remaining added solid indicates saturation.

A full answer includes

• I said clear appearance does not establish unsaturation.
• I proposed adding a little of the same solute, stirring and allowing time at fixed temperature.
• I explained what remaining added solid would show.

Watch for

• “A clear solution must be unsaturated.” — Clear means transparent; it doesn’t tell us whether any more can dissolve.

4. CQ4 · Practice

Model answer. Concentrated; saturated; temperature. A concentrated solution can still be unsaturated.

A full answer includes

• I used concentrated, saturated and temperature in the gaps.
• I distinguished a relative amount from the maximum that can dissolve.

Watch for

• “Concentrated and saturated are interchangeable.” — Concentration describes an amount per amount of solution; saturation says whether more can dissolve at that temperature.

5. CT1 · Apply

Model answer. B is more concentrated: it has more dissolved X in the same water amount. B is saturated at 20°C because it reaches the supplied dissolving limit; A is unsaturated. Clear means transparent and doesn’t distinguish these states. An added small amount could dissolve in A, while some would remain in B after stirring and time at 20°C.

A full answer includes

• I identified B as more concentrated using the equal water amounts.
• I used the 20°C limit to identify B as saturated and A as unsaturated.
• I explained why clear appearance alone cannot distinguish them.

Also accept

• B is more concentrated: it has more dissolved X in the same water amount. B is saturated at 20°C because it reaches the supplied dissolving limit; A is unsaturated. Clear means transparent and does not distinguish these states. An added small amount could dissolve in A, while some would remain in B after stirring and time at 20°C.

Watch for

• “A clear solution must be unsaturated.” — Both samples are clear. Compare their dissolved masses with the supplied limit at 20°C to decide whether more can dissolve.