Question

In ce raport de masa se amesteca doua solutii de acid sulfuric de concentratie 50% si 10% pentru a prepara o solutie de concentratie 20%?
A. 5:1;
B.1:5;
C.3:1;
D.1:3;
E.2:3;
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Answer 1

Varianta directă:

50x-20x = 20y - 10y
30x = 10y
=>raportul molar x:y = 10:30 = 1:3 

sauuuu

$x+y$ grame amestec ............ $\frac{50}{100}x + \frac{10}{100}y$
100 grame amestec ......................... 20

$100(\frac{50}{100}x + \frac{10}{100}y) = 20x + 20y$
$<=>50x+10y = 20x + 20y$
$<=> 50x-20x = 20y-10y$
$<=> 30x = 10y => \frac{x}{y} = \frac{10}{30} = \frac{1}{3}$