When 10 g of magnesium oxide was reacted with sulfuric acid, a salt was obtained. Calculate the mass of this salt.

First, let’s write the interaction reaction to determine the salt:
MgO + H2SO4 = MgSO4 + H2O
We calculate the amount of substance n (MgO) = 10/40 = 0.25 mol. We received the same amount of salt as the reacted magnesium oxide, therefore n (MgSO4) = 0.25 mol. From here we get the mass of salt m (MgSO4) = 120 * 0.25 = 30g.