10g placuta Zn .................... 100% impura
m.pura .................................... 97,5%
= 9,75 g Zn
9,75 - 6,5 = 3,25 g Zn reactionat cu solutia de CuSO4
3,25g md g
Zn + CuSO4 --> ZnSO4 + Cu
65 160
=> md = 3,25x160/65 = 8 g CuSO4
stim ca c% = mdx100/ms
= 8x100/500 = 1,6%