How many grams of acid reacted with magnesium oxide if 40 grams of magnesium sulfate was formed.

Given:
m (MgSO4) = 40 g

To find:
m (H2SO4) -?

Solution:
1) H2SO4 + MgO => MgSO4 + H2O;
2) M (MgSO4) = Mr (MgSO4) = Ar (Mg) * N (Mg) + Ar (S) * N (S) + Ar (O) * N (O) = 24 * 1 + 32 * 1 + 16 * 4 = 120 g / mol;
3) n (MgSO4) = m (MgSO4) / M (MgSO4) = 40/120 = 0.3 mol;
4) n (H2SO4) = n (MgSO4) = 0.3 mol;
5) M (H2SO4) = Mr (H2SO4) = Ar (H) * N (H) + Ar (S) * N (S) + Ar (O) * N (O) = 1 * 2 + 32 * 1 + 16 * 4 = 98 g / mol;
6) m (H2SO4) = n (H2SO4) * M (H2SO4) = 0.3 * 98 = 29 g.

Answer: The mass of H2SO4 is 29 g.