Titration Chemistry

Question

4. A student performed three trials of a titration, each time using 20.00 mL samples of HCl_(aq). The titrant was 0.20 M Ca(OH)_2(aq). The average volume of titrant used was 16.34 mL. What is the concentration of the HCl_(aq)?

Answer 1

The balanced equation for the titration reaction is:

2HCl + Ca(OH)₂ ==> CaCl₂ + 2H₂O ... neutralization reaction

moles Ca(OH)₂ used = 16.34 ml x 1 L / 1000 ml x 0.20 mol / L = 0.003268 moles

moles HCl present = 0.003268 mol Ca(OH)₂ x 2 mol HCl / mol Ca(OH)₂ = 0.006536 moles HCl present

Concentration of HCl = moles/liter = 0.006536 moles / 0.02000 L = 0.3268 M = 0.33 M (2 sig. figs.)