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Safari File Edit View History Bookmarks Develop Window Help * 100% E4 Fri 6:40 PM Q = oho A app.tophat.com Top Hat Food Delivery | Restaurant Takeout | Order Food Online | Grubhub Chegg Study | Guided Solutions and Study Help| Chegg.com + SHOW Homework #1 - due 1/14 100% Close Assigned as Homework O Buffer Q. 3 Acetic acid is a weak acid with a pKa of 4.76. What is the concentration of acetate in a buffer solution of 0.2M at pH 4.9. Give your answer in Mbut as a numeral only to 3 decimal places. Numeric Answer: You are incorrect 1.350 Answered - Sorry, that is not correct. 1 attempt left Retry 9OD DII IO OOO IN TAC GD GE @

Explanation / Answer

According to Henderson-Hasselbulch equation,

pH = pKa + Log([CH3COO-]/[CH3COOH])

i.e. 4.9 = 4.76 + Log{[CH3COO-]/(0.2-[CH3COO-])} (since [CH3COO-] + [CH3COO-] = 0.2)

i.e. Log{[CH3COO-]/(0.2-[CH3COO-])} = 4.9-4.76 = 0.14

i.e. [CH3COO-]/(0.2-[CH3COO-]) = 100.14

i.e. [CH3COO-]/(0.2-[CH3COO-]) = 1.38

i.e. [CH3COO-] = (0.2-[CH3COO-])*1.38

i.e. [CH3COO-] = 0.2*1.38 - [CH3COO-]*1.38

i.e. [CH3COO-] + [CH3COO-]*1.38 = 0.2*1.38

i.e. [CH3COO-]*(1+1.38) = 0.2*1.38

i.e. [CH3COO-] = 0.2*1.38/(1+1.38)

i.e. [CH3COO-] = 0.116 M

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