Calculate the mass of magnesium oxide that can be obtained by thermal decomposition

Calculate the mass of magnesium oxide that can be obtained by thermal decomposition of MgCO3 weighing 100 g, containing. 15% impurities.

Given:

m (MgCO3) = 100 g

w% (impurities) = 15%

To find:

m (MgO) -?

Solution:

MgCO3 = MgO + CO2, – we solve the problem based on the composed reaction equation:

1) Find the mass of pure magnesium carbonate without impurities:

if the proportion of impurities is 15%, then the proportion of pure substance is 85%,

then m (MgCO3) = 100 g * 0.85 = 85 g

2) Find the amount of magnesium carbonate:

n (MgCO3) = m: M = 85 g: 84 g / mol = 1.01 mol

3) We compose a logical expression:

if 1 mole of MgCO3 gives 1 mole of MgO,

then 1.01 mol of MgCO3 will give x mol of MgO,

then x = 1.01 mol.

4) Find the mass of magnesium oxide formed during the reaction:

m (MgO) = n * M = 1.01 mol * 40 g / mol = 40.4 g.

Answer: m (MgO) = 40.4 g.