ACIDS AND BASES Calculating the pH of a weak acid titrated with a strong An anal

Question

ACIDS AND BASES Calculating the pH of a weak acid titrated with a strong An analytical chemist is titrating 186.5 ml of a 0.3100 M solution of butanoic acid (HC3H,Co2) with a 0.9200 M solution of NaOH. The pK, of butanoic acid is 4.82. Calculate the pH of the acid solution after the chemist has added 74.07 mL of the NaOH solution to it. Note for advanced students: you may assume the final volume equals the initial Round your answer to 2 decimal places. valume of the solution plus the volume of NaOH solution added. PH

Explanation / Answer

millimoles of butanoic acid = 186.5 x 0.3100 = 57.815

millimoles of NaOH = 74.07 x 0.9200 = 68.1444

pKa = 4.82

butanoic acid +   NaOH    ----------------> butanoate +   H2O

57.815             68.1444                                   0                0

    0                   10.329                               57.815

here strong base remains. so

concentration of base = 10.329 / (186.5 + 74.07)

                                    = 0.0396 M

pOH = -log [OH-] = -log (0.0396)

pOH = 1.40

pH = 12.60

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