How much water should be taken for the reaction with 250 g of magnesium oxide with an impurity content of 2%?

Let’s write the reaction equation:

MgO + H2O → Mg (OH) 2 (magnesium hydroxide).

Find the mass of magnesium oxide without impurities (98%):

m (MgO) = (m (oxide with impurities) * w (MgO)) / 100% = (250 g * 98%) / 100% = 245 g.

Find the amount of magnesium oxide substance:

n (MgO) = m (MgO) / M (MgO) = 245 g / 40 g / mol = 6.125 mol.

Let’s find the amount of water substance according to the reaction equation:

n (H2O) = n (MgO) = 6.125 mol.

Let’s find the mass of water required for the reaction:

m (H2O) = n (H2O) * M (H2O) = 6.125 mol * 18 g / mol = 110.25 g.

Answer: 110.25 g.