若pH=4.0,过量H2C2O4(c=0.10molL1) c,04间=10.3 Kop-Ksp a c,02听10-78+03=10-75 S= Ksp =10-7.5+1.0=106.5=3×107moL [C204] Ca2+沉淀完全 KMnO4法测Ca2+,MO指示剂 11
11 若pH=4.0，过量H2C2O4 ( c=0.10mol·L-1 ) 2 4 0.3 C O (H) = 10 sp 2 4 -7.5+1.0 -6.5 -7 -1 = = 10 = 10 = 3 10 mol L [C O '] K S Ca2＋沉淀完全 KMnO4法测Ca2＋ ，MO指示剂 Ksp ′= Ksp = 10-7.8+0.3=10-7.5 2- 2 4 C O (H)
例 MnS Ksp=10-12.6,H2SpKa=7.1pKa2=12.9 .K较大，S2定量成为HS,产生同量0H .假设 MnS+H2O=Mn2++HS-+OH- S S S K=[Mn*][HS:I[OH]=[Mn*S*I[H'][OH] Ka2 KpKw=10-12.6-14.0 s 1012.9 =1013.7 Ka2 S=3K=1013.73=104.6molL 12
12 ∵ Ksp较大, S2-定量成为HS- ,产生同量OH- ∴假设 MnS+H2O=Mn2++HS－+OH－ S S S 2+ 2- s + - 2+ - 2 p w - a a 2 -12.6-14.0 -13.7 -12.9 [H ][OH ] = [Mn ][HS ][OH ] = 10 = = = 10 10 [Mn ][S ] K K K K K 3 -13.7/3 - 4.6 -1 S K = = 10 = 10 mol L 例 MnS Kθ sp ＝10-12.6, H2S pKa1=7.1 pKa2=12.9