m = 5,68 g = masa initiala a placutie
a = masa de placuta care a reactionat
b = masa de Pb depusa la finalul reactiei
=> 5,68-a+b = 2x5,68 => -a+b = 5,68
(-a+b) g n g b g
Zn + Pb(NO3)2 => Zn(NO3)2 + Pb
65 331 207
=> a = 65b/207 = 0,314b
=> -0,314b+b = 5,68 => b = 8,28 g Pb depus
=> n = 331xb/207 = 13,24 g Pb(NO3)2 consumata