Prima data gasesti masa moleculara si apoi aplici regula de 3 simpla:
1 mol...A g E...6,023x10^23 at E
x moli...y g E...z at E
*E-element
*^23-la puterea 23
Ex:
b) CO2(dioxid de carbon)
M CO2=A C+2xA O
=12+38
=50 u.a.m.
50gCO2...6,023x10^23atO
11gCO2....x at O
=> x= 11x6,023x10^23 / 50
= 13,2506x10^22
R: 13,2506x10^22 at O