Question

la o solutie de 400g se adauga o substanta dizolvata de 20 g iar noua concentrație =20%.Cat a fost concetratia initiala?

Answer 1

md1 =x

ms1 = 400 g

md2 = x+20 g

ms2 =400+x g

c=100md/ms

c1 = 100x/400

c1 =x/4

c2= (x+20)*100/ (400+x)

20= 100*(x+20)/(400+x)

20*(400+x) = 100*(x+20)

400+x = 5*(x+20)

400+x =5x + 100

4x=300

x=300/4

c1= x/4 =300/16 =18,75%