(1)某CuSO 4溶液里c(Cu 2+)=0.02mol/L,如果生成Cu(OH) 2沉淀,则应有c(OH -)≥
2× 10 -20
0.02 mol/L=10 -9mol/L,则c(H +)≤
1× 10 -14
10 -9 mol/L=10 -5mol/L,
所以pH≥-lg(10 -5)=5,故答案为:5;
(2)Cu 2+沉淀较为完全是的浓度为
0.2mol/L
1000 =2×10 -4mol/L,
则c(OH -)=
2× 10 -20
2× 10 -4 mol/L═10 8mol/L,
则c(H +)=
1× 10 -14
10 -8 mol/L=10 -6mol/L,
所以pH=-lg(10 -6)=6,
故答案为:6.