〈例)求0.1 mol/L H2C2O4,NaHC2O4,Na2C2O4的[H] K=8×102,K,=1×10 (1)H2C2O4 [H]=[HC2O4]+210202]+[OH] 20K=202-201g=25x10°<Ka 1x10 K 故OH舍弃 则H]=HGO]= [H+K 400K=32>C,故K不能舍弃 [H的+H]K-cK=0 [H]=0.058 〈例〉求 0.1 mol/L H2C2O4, NaHC2O4, Na2C2O4 的[H+]。 4 a 2 a 8 10 , 1 10 1 2 − − K = × K = × （1）H2C2O4 [H+] = [HC2O4-] + 2[C2O42-] + [OH-] 2 2 4 1 2 H C O 12 2 4 a W b 2.5 10 8 10 1 10 20 20 20 c KK K = × < ×× = ⋅ = × − −− 故[OH - ]舍弃 则 1 1 [ ] [ ] [ ] 2 4 a a H K K H HCO c + = = + − K c a 400 =32> 1 ，故 a1 K 不能舍弃 [H+ ]2 +[H+] 1 Ka - c 1 Ka = 0 [H+] = 0.058