Din 300 grame solutie de clorura de sodiu de concentratie procentuala masica de 20% se evapora apa si se obtine o solutie de concentratie procentuala 35%.
Calculati masa de apa evaporata din solutie

ms1=300g                         Este vorba de 2 solutii care au acelasi md.
c1=20
                                          c1=md.100:ms1
c2=35
                                          c2=md.100:ms2
mapa evap.                 
                                           Din relatia c1 se afla md.

                                        md=c1.ms1:100

                                        md=20.300:100=60 g Na Cl

                                       Din c2 se afla  ms2.

                                      ms2=md.100:c2

                                      ms2=60.100:35=171 g sol.

                                    Din fiecare sol. se calculeaza masa de apa.

                                     ms1=md+m1apa

                                   m1apa=ms1-md

                                   m1apa=300- 60=240 g

                                  m2apa=ms2-md

                                 m2apa=171-60=111 g

                                mapa evap.=240-111=129g