1. nr moli = masa de Na : masa atomica Na => 96 g Na : 23 g/mol = 4.17 moli
2. Aplici regula de 3 simpla in felul urmator :
In 36.5 g Ca.......6.023 x 10 la 23 atomi
In 50 g Ca........... x atomi => x= (50 x 6.023 x 10la23) : 36.5
=> x = 8.25 x 10la23 atomi
3. Aplici regula de trei simpla in felul urmator :
in 1 mol .... 6.023x10la23 atomi
in y moli .... 30.115x10la24 atomi
y= (30.115x10la24 x 1 ) : 6.023x10la23 => y= 50 moli