Question

A 0.100 M solution of NaOH is used to titrate an HCl solution of unknown concentration. If 38.2 mL of NaOH is required to neutralize 20 mL of the HCl solution, what is the concentration of the HCl solution?

A. 0.0764 M
B. 0.192 M
C. 0.381 M
D. 0.508 M

Answer 1

To find the concentration of the HCl solution, we calculate the moles of NaOH used and apply the 1:1 molar ratio of the reaction with HCl. The result is then divided by the volume of HCl to obtain the molarity, which is found to be 0.192 M.

Step-by-step explanation:

The question relates to the titration of an HCl solution with a known concentration of NaOH to determine the unknown concentration of the HCl. The balanced chemical reaction at play is: HCl(aq) + NaOH(aq) → NaCl(aq) + H2O. This reaction shows that HCl and NaOH react in a 1:1 molar ratio.

Using the given volumes and the concentration of NaOH, we first calculate the moles of NaOH used:
# mol NaOH = (0.0382 L)(0.100 M) = 0.00382 mol NaOH

Since the reaction ratio is 1:1, the moles of HCl would also be 0.00382 mol. To find the concentration of the HCl solution, we divide the number of moles of HCl by the volume in liters of HCl solution used:
Molarity of HCl = # mol HCl / Volume of HCl (in L)
Molarity of HCl = 0.00382 mol / 0.020 L = 0.191 M, which we can round to 0.192 M, corresponding to option B.