Question

1) 2 elevi doresc sa obtina fiecare o solutie de concentratie 5%. Primul foloseste 10g de sare iar celalalt 20g sare. Cata apa sa foloseasca fiecare?

2) Dupa lucrarii de laborator elevii recupereaza solutiile de piatra vanata cu care au lucrat punandu-le intr-un vas. Ce concentratie are solutia din vasul de recuperare stiind ca:
-solitia 1 contine 20g apa si c1=20%
-solutia 2 contine 30g apa si c2=40%

Answer 1

c/100=md1/ms1 => ms1=md1*100/c=10*100/5=200g solutie
c/100=md2/ms2 => ms2=md2*100/c=20*100/5=400g solutie
ms=md+mapa => mapa=ms-md
m1apa=ms1-md1=200-10=190g
m2apa=ms2-md2=400-20=380g
2)
c1/100=md1/(md1+m1apa) => md1*100=c1*md1+c1*m1apa
md1*100-c1*md1=c1*mapa
md1=c1*mapa/(100-c1)=20*20/(100-20)=400/80=5g CuSO4
md2=c2*mapa/(100-c2)=40*30/(100-40)=1200/60=20g CuSO4
ms1=md1+m1apa=5+20=25g solutie
ms2=md2+m2apa=20+30=50g solutie
cfinala/100=(md1+md2)/(ms1+ms2)=25/75 => cfinala=25*100/75=33,33%