In a particular titration experiment, a 30.0-mL sample of an unknown monoprotic acid required 25.0 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 balanced chemical equation for the reaction between a monoprotic acid and NaOH is:

HA + NaOH → NaA + H2O

From the equation, we can see that the mole ratio of HA to NaOH is 1:1. That means the number of moles of NaOH used is equal to the number of moles of HA in the sample.

Number of moles of NaOH used = 0.0250 L × 0.200 mol/L = 0.00500 mol
Number of moles of HA in the sample = 0.00500 mol

The concentration of the acid is then:

concentration = number of moles/volume of sample
concentration = 0.00500 mol/0.0300 L
concentration = 0.1667 M, which is approximately 0.167 M

Therefore, the answer is B.

In a Particular Titration Experiment, a 30