Malachite is an important copper ore with the chemical formula \text{CuCO}_3\cdot\text{Cu(… — JAMB UTME

Malachite is an important copper ore with the chemical formula

\text{CuCO}_3\cdot\text{Cu(OH)}_2

. Upon strong heating, it undergoes thermal decomposition according to the following balanced equation:

\text{CuCO}_3\cdot\text{Cu(OH)}_2(s) \rightarrow 2\text{CuO}(s) + \text{CO}_2(g) + \text{H}_2\text{O}(g)

What is the mass of copper(II) oxide (

\text{CuO}

), in grams, formed when

22.2\text{ g}

of malachite is completely decomposed? [Relative atomic masses:

\text{Cu} = 64

\text{C} = 12

\text{O} = 16

\text{H} = 1

]

Answer: 16 g

The mass of copper(II) oxide produced is 16.0 g.

Thermal decomposition of 1 mole of malachite (

\text{CuCO}_3\cdot\text{Cu(OH)}_2

, molar mass

222\text{ g mol}^{-1}

) produces 2 moles of copper(II) oxide (

\text{CuO}

, molar mass

80\text{ g mol}^{-1}

). Given

22.2\text{ g}

of malachite (

0.1\text{ mol}

), exactly

0.2\text{ mol}

\text{CuO}

is formed, giving a mass of

0.2\text{ mol} \times 80\text{ g mol}^{-1} = 16.0\text{ g}

Calculate the molar mass of malachite,

\text{CuCO}_3\cdot\text{Cu(OH)}_2

222\text{ g mol}^{-1}

Summing the relative atomic masses:

2(64) + 12 + 5(16) + 2(1) = 222\text{ g mol}^{-1}

Calculate the number of moles of malachite in the sample

0.1\text{ mol}

Dividing given mass by molar mass:

\frac{22.2\text{ g}}{222\text{ g mol}^{-1}} = 0.1\text{ mol}

Determine the moles of

\text{CuO}

produced using stoichiometry

0.2\text{ mol}

\text{CuO}

The balanced chemical equation shows a

1:2

mole ratio between malachite and

\text{CuO}

Calculate the mass of

\text{CuO}

formed

16.0\text{ g}

Multiplying moles of

\text{CuO}

by its molar mass (

80\text{ g mol}^{-1}

0.2 \times 80 = 16.0\text{ g}

Stoichiometry of copper compounds thermal decomposition

Question