In a particular titration experiment, a 25.0-mL sample of an unknown diprotic acid required 30.0 mL of 0.200 M NaOH for the end point to be reached. What is the concentration of the acid?
A) 0.120 M
B) 0.167 M
C) 0.240 M
D) 0.333 M

Question

Quizplus · Accepted Answer

The acid is diprotic, so it can donate two protons. The total number of moles of NaOH used is:$$0.0300 	ext{ L} 	imes 0.200 	ext{ mol/L} = 0.00600 	ext{ mol}$$Since the acid is diprotic, the number of moles of acid is half of this:$$0.00600 	ext{ mol} / 2 = 0.00300 	ext{ mol}$$The concentration of the acid is:$$0.00300 	ext{ mol} / 0.0250 	ext{ L} = 0.120 	ext{ M}$$

In a Particular Titration Experiment, a 25