A solution of hydrochloric acid of unknown concentration was titrated with 0.23 M NaOH.If a 100.-mL sample of the HCl solution required exactly 10.mL of the NaOH solution to reach the equivalence point,what was the pH of the HCl solution?

Question

Quizplus · Accepted Answer

At the equivalence point, the moles of HCl will equal the moles of NaOH:
Moles of NaOH = (0.23 mol/L) x (10 mL / 1000 mL) = 0.0023 mol
Since we used 10 mL of NaOH to neutralize 100 mL of HCl, there must have been 0.0023 mol of HCl in that 100 mL of solution. Therefore, the concentration of the HCl solution is:
Concentration of HCl = 0.0023 mol / 0.1 L = 0.023 M
To find the pH of the HCl solution, we can use the formula for the strong acid HCl:
pH = -log[H+]
pH = -log(0.023) ≈ 1.6

A Solution of Hydrochloric Acid of Unknown Concentration Was Titrated