Question

Pentru triplarea concentratiei a 200 g solutie de acid sulfuric cu concentratia de 20% este necesara.....???
a)adaugarea a 200 g de acid
B)evaporarea a 100 de grame de apa
c)adaugarea a 100 de grame de acid
D)adaugarea a 200 de grame de solutie de acid,de concentratie 80%
E)adaugarea a 20 de grame de acid

Answer 1

se aplica relatia : c=mdx100/ms
 
c1=20%    ms1=200g     md1= c1xms1/100= 40g
c2= 60% 

a.masa de acid se adauga si la md si la ms
md2= md1+200=240g
ms2=ms1+200=400g
c2= 240x100/400= 60%   corect!
deci cad punctele c.si e.

b. scade ms prin evaporarea apaei; md ramane constant
.md2=md1=40g
   ms2=ms1-100= 100g
c2=40x100/100=40%---incorect !

d ,se adauga la md1 si la ms1 ,md si ms din a doua solutie

80/100=md/200--> md=160g
  md2= md1+160= 2oog
   ms2= ms1+200=400g
  c2=200x100/400=50%    incorect !