If a reagent is more concentrated, what happens to the volume needed?

• A. The volume decreases.
• B. The volume increases.
• C. The mass decreases.
• D. The concentration changes.

Answer: (A)

The amount of solute you need is fixed, so the volume required is controlled by how concentrated the reagent is. The relationship is n = C × V, where n is the amount of solute, C is concentration, and V is volume. If you keep n the same and increase C, the volume V must decrease (V = n/C). For example, doubling the concentration halves the volume needed to supply the same amount of solute. So when a reagent is more concentrated, the volume required decreases.