$1)CH_3COOH\rightleftharpoons CH_3COO^-+H^+$Trong $1 lit\Rightarrow m_{CH_3COOH}=6 gam\Rightarrow n_{CH_3COOH}=0,1 mol$
$\Rightarrow C_{o(CH_3COOH)}=\frac{0,1}{1}=1 M\Rightarrow [H^+]=\alpha C_o=\frac{1,0.0,1}{100}=10^{-3} M$
$2)HCOOH\rightleftharpoons HCOO^-+H^+$
Trong $1 lit\Rightarrow m_{HCOOH}=4,6 gam\Rightarrow n_{HCOOH}=0,1 mol$
$\Rightarrow C_o=0,1 M\Rightarrow \alpha C_o=10^{-3}\Rightarrow \alpha =0,01\Rightarrow \alpha =1 \%$
$3)CH_3COOH\rightleftharpoons CH_3COO^-+H^+$
$\Rightarrow [H^+]=\frac{1.0,1}{100}=10^{-3}\Rightarrow pH=-lg[H^+]=3$