sulfura de Na este Na2S
masa moleculara este 23*2+32=78
78 g Na2S contin 46 g Na
15.6 g........................x
x= 15.6*46/78=9.2 g Na
1 mol NA (adica 23 g) contin 6.022*10p23 ioni Na
9.2...................................................y
y= 9.2*6.022*10p23/23=2.4088*10p23 ioni de Na, p=putere