What are the concentrations of acetic acid (pKa = 4.76) and acetate in a buffer

Question

          What are the concentrations of acetic acid (pKa = 4.76) and acetate in a buffer solution of 0.20 M at pH 4.9? Enter your answer to two significant figures. (For example, 0.0090 and 0.0097 each have two significant figures, whereas 0.009 has only one significant figure.)           What are the concentrations of acetic acid (pKa = 4.76) and acetate in a buffer solution of 0.20 M at pH 4.9? Enter your answer to two significant figures. (For example, 0.0090 and 0.0097 each have two significant figures, whereas 0.009 has only one significant figure.)      What are the concentrations of acetic acid (pKa = 4.76) and acetate in a buffer solution of 0.20 M at pH 4.9? Enter your answer to two significant figures. (For example, 0.0090 and 0.0097 each have two significant figures, whereas 0.009 has only one significant figure.) What are the concentrations of acetic acid (pKa = 4.76) and acetate in a buffer solution of 0.20 M at pH 4.9? Enter your answer to two significant figures. (For example, 0.0090 and 0.0097 each have two significant figures, whereas 0.009 has only one significant figure.)

Explanation / Answer

pH= pKa+ log ([salt]/[acid])

4.9=4.76+log ([salt]/[acid])

log ([salt]/[acid])=49-4.76=0.14

So ([salt]/[acid])=10^0.14=1.38

ratio of concentration acetate /acid =1.38

Total concentration of acetate +acid =0.1

so if concentrations of acetic acid is x , concentration of acetate is1.38x

x+1.38x =2.38x =0.1

x=0.042M and aetate 0.1-0.042=0.058 M

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