NaOH + HCl ---> NaCl + H2O.
c NaOH = md NaOH/ms NaOH * 100=>md NaOH = 200*40/100=80 g NaOH.
40 g NaOH........36,5 g HCl.
80 g NaOH..........x g HCl. x = 73 g HCl = md.
ms HCl = md HCl/c HCl * 100 = 73/36.5*100=200 g soluție.
ms final = 200+200=400 g.
md final = 80 + 73 = 153 g.
c% finală = 153/400*100=>c%=38.25%.