Question

Calculati masa (grame) de apa care trebuie evaporata din 200g solutie NaCl cu concentratia procentuala masica 20% pentru a obtine o solutie de concentratie procentuala masica 40%.

Answer 1

intai calculam masa de NaCl
md=c*ms/100=20*200/100=40g NaCl
notam masa de apa evaporata cu x
la evaporare, masa de sare nu se modifica => md=mdfinal=40g NaCl
msfinal=ms-x=200-x
cfinal=mdfinal*100/msfinal=40*100/(200-x)=40 => 200-x=40*100/40=100 => x=200-100=100g apa