Titration Question

Question

You titrate 25.0 mL of HCl solution of an unknown concentration with a 0.160 M NaOH solution. Complete neutralization of the HCl solution requires the addition of 41.6 mL of titrant.

Calculate the concentration of the HCl solution.

Answer 1

We know the volume of the HCl solution, so in order to calculate concentration, we need to know the amount of moles present in the solution. Complete neutralization occurs when the amount of moles of the titrant (NaOH) equals the amount of moles of the analyte (HCl). Therefore, we can find the amount of moles HCl present by calculating how many moles of NaOH were added. Remember to convert volumes from mL to L.

From Moles = Molarity * Volume

Moles NaOH = .160M NaOH * .416 L = .06656 moles NaOH

As stated before, complete neutralization occurs when the moles NaOH and moles HCl are equal. So there were .06656 moles HCl in the 25 mL of HCl initially present. Therefore the concentration of the solution is:

Molarity = Moles / Volume

[HCl] = .06656 moles HCl / .025 L = 2.6624 M

The values we were given only had 3 significant digits, so our final answer is 2.66 M.

If you have trouble remembering that logic flow, memorize this equation:

[Solution] = ([Titrant] * Volume Titrant Added) / Volume Solution

2.66 M HCl = (.160 M NaOH * .416 L)/.025 L