Scrii ecuatia reactiei chimice
Al2O3 + 6 HCl --> 2 AlCl3 + 3 H2O
aplici regula de 3 simpla in ecuatie folosind nr de moli
la 1 mol Al2O3........6 moli HCl
la 20 mmoli Al2O3..........x mmoli HCl x=120mmoli HCl
nr moli=masa substantei/masa molara=>masa = nr moli * masa molara
masa = (120 * 36,5)/1000=4,38 g = md HCl
Imparti cu 1000 deoarece 1 mol = 1000 mmoli
c%=(md/ms)*100=>ms=(md/c)*100=(4,38/25)*100=>ms=17,52 g HCl
