concentratia / 100 = masa dizolvata / masa solutiei
concentratia = 65%
masa solutiei = 1,5 kg = 1500 g
masa dizolvata = c x ms : 100 =65 x 1500 : 100 = 975 grame NaCl
1 mol NaCl = 23 + 35,5 = 58,5 grame
nr mol NaCl = masa NaCl : masa molara = 975 g : 58,5 g = 16.67 mol