Question

A 50.0-mL volume of 0.15 M HBr is titrated with 0.25 M KOH. Calculate the pH...

A 50.0-mL volume of 0.15 M HBr is titrated with 0.25 M KOH. Calculate the pH after the addition of 19.0 mL of KOH.

Express your answer numerically.

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Answer #1

Given:

M(HBr) = 0.15 M

V(HBr) = 50 mL

M(KOH) = 0.25 M

V(KOH) = 19 mL

mol(HBr) = M(HBr) * V(HBr)

mol(HBr) = 0.15 M * 50 mL = 7.5 mmol

mol(KOH) = M(KOH) * V(KOH)

mol(KOH) = 0.25 M * 19 mL = 4.75 mmol

We have:

mol(HBr) = 7.5 mmol

mol(KOH) = 4.75 mmol

4.75 mmol of both will react

remaining mol of HBr = 2.75 mmol

Total volume = 69.0 mL

[H+]= mol of acid remaining / volume

[H+] = 2.75 mmol/69.0 mL

= 3.986*10^-2 M

use:

pH = -log [H+]

= -log (3.986*10^-2)

= 1.3995

Answer: 1.40

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