Calculate the mass of magnesium oxide, which is formed when firing magnesium carbonate weighing 200 g, containing 10% impurities.

1.Let’s find the mass of magnesium carbonate without impurities.

100% – 10% = 90%.

200 g – 100%.

X – 90%.

X = (200g × 90%): 100% = 180g.

Let’s find the amount of MgCO3 substance by the formula:
n = m: M.

M (MgCO3) = 142 g / mol.

n = 180 g: 84 g / mol = 2.14 mol.

Let’s compose the reaction equation, find the quantitative ratios of substances.

MgCO3 → MgO + CO2 ↑.

According to the reaction equation, there is 1 mole of MgO per 1 mole of MgCO3.

The substances are in quantitative ratios of 1: 1.

The amount of substance will be equal.

n (MgO3) = n (MgO) = 2.14 mol.

Let’s find the mass of MgO.

M (MgO) = 40 g / mol.

m = n × M.

m = 40 g / mol × 2.14 mol = 85.6 g.

Answer: 85.6 g.