CH3COOH==CH3COO- + H+
0.025-× 0.025+x X
代入平衡常数K= (0.025 +x) ×／（0.025-x) 因为k值小,x也很小,这里近视处理：
0.025+x ==0.025 ,0.025 - x ==0.025 ,故有 x==1.75 x 10-5
c(H+)==1.75 X 10-5 再取对数,pH =4.8