Question

avem o solutie cy masa de 400 g .Se adauga 200 g apa, iar concentratia devine 20% .Aflati concentratia procentuala.

Answer 1

concentratia / 100 = masa dizolvata  / masa solutiei 

solutia initiala are masa ms = 400 grame 
se adauga 200 grame si masa solutiei devine ms1 = ms + 200g = 400+200 = 600 grame 
concentratia c1 =20%
aflam masa dizolvata, care e aceeasi in ambele situatii 
 
masa dizolvata = ms1 x c1 : 100 = 600 x 20 : 100 = 120 grame 

in solutia initiala, c = md x 100 : 400 = 120 x 100 : 400 = 30%