2 NaOH + H2SO4 ---> Na2SO4 + 2 H2O
2 moli NaOH........1 mol H2SO4
0,2 moli NaOH..........x moli H2SO4 x = 0,1 moli H2SO4=0,1*98 g=9,8 g H2SO4
c%=md/ms*100=>ms = md/c *100=9,8/49*100=20 g solutie H2SO4
md final = nr moli NaOH * masa molara NaOH = 0.2*40=8 g
ms final = masa solutiei de H2SO4 = 20 g
c%=md/ms*100=8/20*100=>c% = 40 %