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?

Answer: (a) 0.1M

(b) pH = 1

Explanation:

Moles = Molarity * Volume me (L)

The initial number of moles in the flask = 0.5M * 0.010L = 0.005moles

After the addition of 40 mL of in the flask again, the total volume in the flask = 10 mL + 40 mL = 50 mL

Concentration = Moles/Volume (L) [H3O+]

=

0.005moles/0.050L = 0.1M

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

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