A 4.00\text{ g} sample of an impure copper(II) oxide ore is heated in a stream of dry hydr… — JAMB UTME

4.00\text{ g}

sample of an impure copper(II) oxide ore is heated in a stream of dry hydrogen gas until reduction is complete according to the equation:

\text{CuO}_{(s)} + \text{H}_{2(g)} \rightarrow \text{Cu}_{(s)} + \text{H}_2\text{O}_{(g)}

2.54\text{ g}

of pure copper metal is obtained, what is the percentage purity of the copper(II) oxide in the ore?

[\text{Relative atomic masses: Cu} = 63.5, \text{O} = 16.0]

The percentage purity of the copper(II) oxide in the ore is

79.5\%

The option stating

79.5\%

is correct because

2.54\text{ g}

of copper corresponds to

0.04\text{ mol}

\text{Cu}

. According to the chemical equation,

0.04\text{ mol}

\text{Cu}

requires

0.04\text{ mol}

of pure

\text{CuO}

, which weighs

0.04 \times 79.5\text{ g mol}^{-1} = 3.18\text{ g}

. Dividing

3.18\text{ g}

of pure

\text{CuO}

by the total sample mass of

4.00\text{ g}

yields

79.5\%

Calculate the molar mass of copper(II) oxide (CuO) and the moles of copper metal produced.

\text{Molar mass of CuO} = 63.5 + 16.0 = 79.5\text{ g mol}^{-1}

\text{Moles of Cu} = \frac{2.54\text{ g}}{63.5\text{ g mol}^{-1}} = 0.04\text{ mol}

Converting the given mass of product into moles allows stoichiometric ratio calculations.

Determine the moles and mass of pure copper(II) oxide in the sample.

From the equation,

1\text{ mol CuO} \rightarrow 1\text{ mol Cu}

. Moles of pure

\text{CuO} = 0.04\text{ mol}

. Mass of pure

\text{CuO} = 0.04\text{ mol} \times 79.5\text{ g mol}^{-1} = 3.18\text{ g}

Stoichiometry dictates that 1 mole of CuO produces 1 mole of Cu upon complete reduction.

Calculate the percentage purity of the copper(II) oxide sample.

\text{Percentage purity} = \frac{\text{Mass of pure CuO}}{\text{Total mass of sample}} \times 100\% = \frac{3.18\text{ g}}{4.00\text{ g}} \times 100\% = 79.5\%

Percentage purity is the ratio of pure reactive compound mass to total impure sample mass expressed as a percentage.

Determining percentage purity using stoichiometric reduction yields

Question