Question

1) La 200g solutie NaOH de concentratie 30% se adauga 100g apa. Care este concentratia solutiei noi?
2) In 400g solutie de sare de concentratie 10% se adauga 40g de sare. Ce concentratie are noua solutie?

Answer 1

1)ms=200g
c=20%
m a=masa apei adăugată=100g

$c = \frac{md}{ms} \times 100 \\ md = \frac{c \times ms}{100} \\ md = \frac{30 \times 200}{100} = 60g$
ms1=ms+ ma=200+100=300g

$c1 = \frac{md}{ms1} \times 100 \\ c1 = \frac{60}{300} \times 100 = 20\%$
2)ms=400g
c=10%
md a=masa de sare adăugată=40g
$c = \frac{md}{ms} \times 100 \\ md = \frac{c \times ms}{100} \\ md = \frac{10 \times 400}{100} = 40 \: g$
md1=md+md a=40+40=80g
ms1=ms+md a+400+40=440g
$c1 = \frac{md1}{ms1} \times 100 \\ c1 = \frac{80}{440} \times 100 = 18.18\%$