Cho hỗn hợp Na và Mg lấy dư vào 100 g dung dịch H2SO4 20% thì thể tích khí H2 (đktc) thoát ra là A. 4,57 lít. B. 54,35 lít. C. 49,78 lít. D. 57,35 lít. Lời giải: Đáp án B Trong 100g dung dịch H2SO4có \(\left\{ \matrix{20g\,{H_2}S{O_4} \hfill \cr 80g\,{H_2}O \hfill \cr} \right.\) \(\eqalign{ & {H_2}S{O_4}\,\,\,\,\,\,\,\,\, \to \,\,\,\,\,\,\,\,\,\,\,\,\,{H_2} \cr & 98g\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,22,4\,lít \cr & 20g\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{V_1} \cr & {V_1} = {{22,4.20} \over {98}} = 4,57\left( {lit} \right) \cr & {H_2}S{O_4}\,\,\,\,\,\,\,\,\, \to \,\,\,\,\,\,\,\,\,\,\,\,{1 \over 2}{H_2} \cr & 18g\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,11,2\,lít \cr & 80g\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{V_2} \cr & V = {V_1} + {V_2} = 4,57 + 49,78 = 54,35\left( {lít} \right) \cr} \)
