Question 3 of 32 eneral Chemistr Donald McQuarrie Peter A. Rock Ethan Gallogy Un

Question

Question 3 of 32 eneral Chemistr Donald McQuarrie Peter A. Rock Ethan Gallogy University Science Books presented by Sapling Learning You need to prepare 100.0 mL of a pH4.00 buffer solution using 0.100 M benzoic acid (pKa 4.20) and 0.200 M sodium benzoate. How much of each solution should be mixed to prepare this buffer? Number mL benzoic acid Number mL sodium benzoate O Previous Previous Give Up& View SolutionCheck AnswerNextExit Give Up & View Solution O Check Answer 0 Next I Exit- Hint The sum of the volumes should be 100.0 mL

Explanation / Answer

As per Henderson's equation:-

pH = pKa + log{[Salt]/[Acid]}

or, pH = pKa + log{[sodium benzoate]/[benzoic acid]}

or, 4 = 4.2 + log[(0.2*x)/(0.1*(100-x))] ; where x = volume of sodium benzoate

or, 10-0.2 = [(0.2*x)/(0.1*(100-x))]

or, 0.3155 = x/(100-x)

or, 23.98 = x = volume of sodium benzoate

Thus, volume of benzoic acid = 100 - 23.98 = 76.02 ml

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