se afla Mg pur ; se aplica formula puritatii ; p=mp.100 : mt
mp =p. mt: 100=80 .30 : 100
= 24 g Mg pur
24g xg
2Mg + O2 = 2MgO
2.24 g 2. 40g
MMgO= 24+16=40------> 1mol=40g [ 40g/mol ]
x=24.2.40 : 2. 24=40 g MgO
se afla nr. de moli
n=m: M = 40g : 40g/moli=1mol MgO