Suppose you have 16.2 mL of a 0.250 M HCl solution that weighs 16.7 grams.

Question

How many moles of HCl are in the solution?

Answer 1

The mass of this solution is a red herring, meaning it is a useless piece of information. We only need the volume (16.2 mL) and the molarity (0.250 M).

We need to do two conversions, one from mL --> L, another from L --> mol.

(16.2 mL) x (1 L / 1000 mL) x (0.250 moles / 1 Liter) = 0.00405 = 4.05 x 10^-3

Hope this helps!