Cách 1:
nH2 = \(\dfrac{1,12}{22,4}=0,05\left(mol\right)\)
(a)+(b) PTHH: \(Mg+H_2SO_4\) \(\rightarrow MgSO_4+H_2\)
pư.......................0,05......0,05............0,05........0,05 (mol)
\(\Rightarrow m_{Mg}=24.0,05=1,2\left(g\right)\)
\(\Rightarrow m_{MgO}=8,6-1,2=7,4\left(g\right)\)
\(\Rightarrow n_{MgO}=\dfrac{7,4}{40}=0,185\left(mol\right)\)
PTHH: \(MgO+H_{2_{ }}SO_4\rightarrow MgSO_4+H_2O\)
pư..........0,185......0,185..........0,185.........0,185 (mol)
c) \(m_{H2SO4}=98.\left(0,05+0,185\right)=23,03\left(g\right)\)
\(\Rightarrow m_{ddH2SO4}=\dfrac{23,03}{20\%}=115,15\left(g\right)\)
Vậy......