Calculating the pH of a weak acid titrated with a strong b.. An analytical chemi

Question

Calculating the pH of a weak acid titrated with a strong b.. An analytical chemist is trating 137.1 ml of a 0.7800 M solution of formic acda (H,CO) with a 0,5500 Mt solution of KOH. The pk, of formic acd is 3.74 Calculate the pt of the acid solution after the chemist has added 212.7 ml of the KOH solution to it. Note for advanced students: you may assume the final volume equals the initial volume of the solution plus the volume of KOH solution added Round your answer to 2 decimal places. olo pH Explanation

Explanation / Answer

Ans. 137.1 mL of 0.7800 M solution of formic acid = 107 mMol

and 212.7 mL of 0.5500 M solution of KOH = 117 mMol

The rection will give potassium formate (107 mmol) and excess KOH

and mMol of KOH remaining = 117-107 = 10 mMol

total volume of solution 349.8 mL.

molarity of KOH = 10/349.8 = 0.0285 M = [OH-]

now pOH?=?log[OH?]= -log (0.0285) = 1.545

pH + pOH = 14

pH = 14 - 1.545

=12.45

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