A buffer solution is prepared by mixing 44.6 mL of 0.0597 M sodium hydrogen citr
ID: 693725 • Letter: A
Question
A buffer solution is prepared by mixing 44.6 mL of 0.0597 M sodium hydrogen citrate with 55.1 mL of 0.380 M sodium citrate. A table of pKa values can be found here. 1. Calculate the pH (to two decimal places) of this solution. Assume the 5% approximation is valid and that the volumes are additive. Submit Answer Tries 0/3 2. Calculate the pH (to two decimal places) of the buffer solution after the addition of 215 mL of a 0.00335 M solution of barium hydroxide to the existing buffer solution. Assume the 5% approximation is valid and that the volumes are additive. Submit AnswerTries 0/3 This discussion is closed. Send FeedbackExplanation / Answer
1) pH of buffer = pka2 + log(sodium citrate / sodium hydrogen citrate)
pka2 of citric acid = 4.761
no of mol of sodium citrate taken = 55.1*0.38 = 20.938 mmol
no of mol of sodium hydrogen citrate taken = 44.6*0.0597 = 2.663 mmol
pH = 4.761+log(20.938/2.663)
= 5.65
2) no of mol of Ba(OH)2 added = 215*0.00335 = 0.72 mmol
pH of buffer = pka2 + log(sodium citrate+2*Ba(OH)2 / sodium hydrogen citrate -2*Ba(OH)2)
pH = 4.761+log((20.938+2*0.72)/(2.663-2*0.72))
= 6.02
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