\(\rm K_a<<\) nên coi \(\rm [C_2H_5COOH]=C_{C_2H_5COOH};[CH_3COOH]=C_{CH_3COOH}\)
\(\rm K_a(CH_3COOH).C_{CH_3COOH};K_a(C_2H_5COOH).C_{C_2H_5COOH}>>K_W\)
\(\to\) Bỏ qua phân li nước.
\(\rm [H^+]= [C_2H_5COO^-]+[CH_3COO^-]\)
\(\rm\to [H^+]=\dfrac{K_a.[C_2H_5COOH]}{[H^+]}+\dfrac{K_a.[CH_3COOH]}{[H^+]}\)
\(\rm\to [H^+]=\dfrac{10^{-5,24}.0,2+10^{-4,76}.0,5}{[H^+]}\)
\(\rm\to [H^+]\approx 3,14.10^{-3}\)
\(\rm\to pH=-log[H^+]\approx 2,503\)