Question

peste 40 kg de solutie de soda caustica de concentratie 16% se adauga soda caustica pana cand concentratia devine 20% . Ce masa de substanta s-a adaugat?

Answer 1

ms1=40 kg
c1=16%
md1=ms1*c1/100=40*16/100=6,4 kg
Notam cu m masa de substanta adaugata
md2=md1+ m
ms2=ms1+ m
c2=20%
(md1+m)/(ms1+m)=20/100
100*(md1+m)=20*(ms1+m)
100*(6,4+m)=20*(40+m)
640+100*m=800+20*m
80*m=160
m=20 kg substanta s-a adaugat