Question

2-Ce masa de apa trebuie adaugata la 0.2kg solutie KCl de concentratie 30% pentru a obtine o solutie de concentratie 10%?

Answer 1

concentratia / 100 = masa dizolvata / masa solutiei

prima solutie   
30/ 100 = md / 200    ==> md = 30 x 200 / 100 = 60 grame KCl

a doua solutie 
10 / 100 = 60/msol     masa sol = 60 x 100 / 10 = 600 grame sol 10%

600 grame - 200 grame = 400 grama apa adaugate