Given the Ka for acetic acid is 1.77×10−5 and Kb for ammonium hydroxide is 1.82×10−5.
Calculate the pH of an aqueous solution of ammonium acetate (CH3COONH4) at 25∘C.
A
8.115
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B
7.01
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C
7.65
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D
8.05
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Solution
The correct option is B 7.01 pKa=−log(Ka)pKa=−log(1.77×10−5)=(5−0.25)pKa=4.75
pKb=−log(Kb)pKb=−log(1.82×10−5)=(5−0.26)pKb=4.74
For a salt of weak acid and weak base pH is given as: pH=7+12(pKa−pKb)pH=7+12(4.75−4.74)pH=7+0.012pH=7.005