Question

determina masa de apa care trebuie adaugata peste 400g de solutie cu c=30% pentru a obtine o solutie cu c=24%

Answer 1

C=md*100/ms
md=ms*C/100=120
24=120*100/ms
ms=120*100/24=500
R: trebuie adaugata inca 100g de H2O

Answer 2

masa solutiei=ms=400g
concentratia procentuala initiala=cp1=30%
concentratia procentuala finala=cp2=24%

Avem formula:

concentratia procentuala= masa de substanta dizolvata/masa solutiei * 100

cp1=md/ms * 100

30/100= md/400 ===> md= 30*400/100= 30*4 =120g
md=120g

cp2=md/ms * 100
masa solutiei= masa substantei dizolvate + masa de apa

cp2= md/(md+ mH2O ) *100

24/100= 120/(120+mH2O)

120+mH2O= 100*120/24

120+mH2O= 100 * 5

mH2O=500-120

mH2O=380g

Peste cantitatea de 400g de solutie se mai adauga :

m apa adaugata=(msf -msi)=
=md+mH2O-msi=
= 120+380-400=
=500-400= 100g apa