A sample of hydrated copper(II) sulfate (\text{CuSO}_4 \cdot 5\text{H}_2\text{O}) has a ma… — JAMB UTME

A sample of hydrated copper(II) sulfate ( $\text{CuSO}_4 \cdot 5\text{H}_2\text{O}$ ) has a mass of $24.95\text{ g}$ . What is the total number of moles of oxygen atoms contained in this sample? $[\text{Relative atomic masses: } \text{Cu} = 63.5, \text{S} = 32.0, \text{O} = 16.0, \text{H} = 1.0]$

Answer: 0.9 mol

Answer

The total number of moles of oxygen atoms contained in the sample is

0.90\text{ mol}

The molar mass of hydrated copper(II) sulfate (

\text{CuSO}_4 \cdot 5\text{H}_2\text{O}

) is

249.5\text{ g/mol}

. Dividing

24.95\text{ g}

249.5\text{ g/mol}

gives

0.10\text{ mol}

of the compound. Since each mole of

\text{CuSO}_4 \cdot 5\text{H}_2\text{O}

contains

9\text{ moles}

of oxygen atoms (

4

from

\text{CuSO}_4

and

5

from

5\text{H}_2\text{O}

), the total quantity of oxygen atoms is

0.10 \times 9 = 0.90\text{ mol}

Step-by-Step Solution

Calculate the molar mass of

\text{CuSO}_4 \cdot 5\text{H}_2\text{O}

Molar mass =

249.5\text{ g/mol}

Sum the relative atomic masses of all atoms present in one formula unit of the hydrated compound.

Calculate the moles of the hydrated salt

Moles of compound =

0.10\text{ mol}

Divide the mass of the sample (

24.95\text{ g}

) by its molar mass (

249.5\text{ g/mol}

Determine the stoichiometric multiplier for oxygen atoms

9 moles of oxygen atoms per mole of compound

Each formula unit contains 4 oxygen atoms in the sulfate group and 5 oxygen atoms in the water of crystallization.

Calculate total moles of oxygen atoms

Moles of oxygen atoms =

0.90\text{ mol}

Multiply the moles of compound (

0.10\text{ mol}

) by the 9 moles of oxygen atoms per mole of compound.

Key Concept

Stoichiometric relationship of constituent atoms in a hydrated compound

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