Question

The solubility level of an aqueous solution of NaCl at 25°C is:

• A. 20g
• B. 36g
• C. 95g
• D. 8g

Hint:

Solubility is the maximum amount of solute that can dissolve in a solvent at a given temperature, which for NaCl at 25°C is 36g per 100g of water.

Answer 1

The Correct Option is B

Think about dissolving table salt into a small glass of water at room temperature and stirring until no more will dissolve.

1. 20g: a home experiment shows more salt than this can still dissolve before the water becomes saturated, so this figure is too low.
2. 36g: this matches the commonly quoted solubility of ordinary table salt in 100 mL of water at room temperature, the point at which no more salt will dissolve.
3. 95g: this is an unrealistically large amount for table salt to dissolve in such a small amount of water at room temperature.
4. 8g: a kitchen test easily dissolves far more salt than this small amount before the water is anywhere close to saturated.

Since ordinary table salt matches the commonly quoted 36 gram figure in this amount of water, that is the correct answer.

Answer 2

Compare NaCl's solubility to other common salts to judge whether each option is a reasonable order of magnitude.

1. 20g: some less soluble salts fall near this figure, but NaCl is known to dissolve more than this in the same volume of water.
2. 36g: NaCl is a moderately soluble ionic salt, dissolving well but not exceptionally so, and this figure matches its well documented solubility in water at room temperature.
3. 95g: a solubility this high belongs to salts that are far more soluble than NaCl, not to ordinary table salt.
4. 8g: a solubility this low belongs to a poorly soluble salt, well below where NaCl actually sits.

NaCl's moderate ionic solubility lines up with the 36 gram figure, making that the correct answer.