A 10 mL sample of HCl solution was transferred by pipet to an Erlenmeyer flask and then diluted by adding about 40 mL of distelled water. What is the approximate H3O+ concentration and pH of the solution in the flask before the titration begins?

The approximate H3O+ concentration before the titration begins is 0.1 M

pH of the solution in the flask is 1

Explanation:

Initial concentration of HCl = 0.5 mol/L

Initial number of mols in Erlenmeyer flask = (0.5 mol/L)(0.010 L) = 0.005 mol

After addition of 40 mL of volume to the flask again, the total volume in the flask = 50 mL

Therefore - the resultant [H3O+] concetration in the solution = 0.005 mol / 0.050 L = 0.1 M (before titration begins)

Hence - pH = -log[H3O+] = -log (0.1) = 1