In a different experiment, a student had 10.0 mL of 0.020 M HCl. Again, much to the surprise of the student, it took only 5.00 mL of 0.020 M strong base to react completely with the HCl. Explain why it took only half as much strong base to react with all of the HCl.

molar ratio 1:2 (1 mol HCl=2 mol of base)

Explanation:

We have the same concentration for the acid and the base and we have half of the volume therefore we have to keep in mind that we have a 1:2 molar ratio.

If we have a 1:2 molar ratio between the acid and the base we will need half of the volume of the base.