5 moli de apa inseamna 5*18=90 grame apa
0,2 kg solutie inseamna 200 grame solutie (ms)
Din concentratia initiala aflam masa de substanta dizolvata md:
C=md*100/ms
md=C*ms/100
md=40 g
Noua concentratie va avea ms'=ms + 90=290 grame solutie
C=md*100/ms'
C=40*100/290
C=13,8%