A Level Chemistry OCR Practice Exam

What does concentration measure in a solution?

1. The volume of solute in a solution

2. The mass of solution in kilograms

3. The amount of solute per 1 dm³ of solution

4. The temperature of the solution

The correct answer is: The amount of solute per 1 dm³ of solution

Concentration measures the amount of solute present in a given volume of solution, typically expressed as the number of moles of solute per liter of solution (or per 1 dm³). This concept is fundamental in chemistry because it allows us to understand how much of a substance is dissolved in a certain volume, which can affect reaction rates, equilibria, and properties of the solution. The other options do not accurately describe concentration. The volume of solute alone does not provide a measure of how concentrated the solution is, since it doesn't account for the total volume of the solution. Similarly, the mass of the solution as a whole does not inform us specifically about the amount of solute present relative to that volume. Lastly, concentration is not related to temperature, which affects solubility but does not define how concentration is measured. Thus, the choice indicating the amount of solute per 1 dm³ of solution correctly encapsulates the definition of concentration.