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Difficulty: HardCopper: Extraction, Physical and Chemical Properties, and Compounds

A sample of hydrated copper(II) tetraoxosulfate(VI), CuSO4⋅5H2O\text{CuSO}_4\cdot 5\text{H}_2\text{O}, with a mass of 12.5 g12.5\text{ g} is dissolved completely in distilled water to make 250 cm3250\text{ cm}^3 of solution. What is the concentration of the copper(II) tetraoxosulfate(VI) solution in mol dm−3\text{mol dm}^{-3}?

(Relative atomic masses: Cu=64, S=32, O=16, H=1\text{Relative atomic masses: Cu} = 64,\text{ S} = 32,\text{ O} = 16,\text{ H} = 1)

  1. A
    0.05 mol dm−30.05\text{ mol dm}^{-3}
  2. 0.20 mol dm−30.20\text{ mol dm}^{-3}Answer
  3. C
    0.31 mol dm−30.31\text{ mol dm}^{-3}
  4. D
    50.00 mol dm−350.00\text{ mol dm}^{-3}

Answer

The molar concentration of the copper(II) tetraoxosulfate(VI) solution is 0.20 mol dm−30.20\text{ mol dm}^{-3}.
The correct concentration is 0.20 mol dm−30.20\text{ mol dm}^{-3}. The molar mass of hydrated copper(II) tetraoxosulfate(VI) (CuSO4⋅5H2O\text{CuSO}_4\cdot 5\text{H}_2\text{O}) is 250 g mol−1250\text{ g mol}^{-1}, so 12.5 g12.5\text{ g} corresponds to 0.05 mol0.05\text{ mol}. Dividing 0.05 mol0.05\text{ mol} by the volume of 0.25 dm30.25\text{ dm}^3 gives 0.20 mol dm−30.20\text{ mol dm}^{-3}.

Step-by-Step Solution

1
Calculate the molar mass of hydrated copper(II) tetraoxosulfate(VI), CuSO4⋅5H2O\text{CuSO}_4\cdot 5\text{H}_2\text{O}.
Molar mass=64+32+(4×16)+5×(2×1+16)=250 g mol−1\text{Molar mass} = 64 + 32 + (4 \times 16) + 5 \times (2 \times 1 + 16) = 250\text{ g mol}^{-1}.
The total molar mass must include the 5 molecules of water of crystallization present in the solid salt.
2
Determine the number of moles of CuSO4⋅5H2O\text{CuSO}_4\cdot 5\text{H}_2\text{O} dissolved.
Moles=12.5 g250 g mol−1=0.05 mol\text{Moles} = \frac{12.5\text{ g}}{250\text{ g mol}^{-1}} = 0.05\text{ mol}.
Number of moles is equal to the given mass divided by the molar mass.
3
Convert the volume of the solution from cm3\text{cm}^3 to dm3\text{dm}^3.
Volume=250 cm31000=0.25 dm3\text{Volume} = \frac{250\text{ cm}^3}{1000} = 0.25\text{ dm}^3.
Molar concentration requires the volume of solution to be expressed in cubic decimetres.
4
Calculate the molar concentration in mol dm−3\text{mol dm}^{-3}.
Concentration=0.05 mol0.25 dm3=0.20 mol dm−3\text{Concentration} = \frac{0.05\text{ mol}}{0.25\text{ dm}^3} = 0.20\text{ mol dm}^{-3}.
Molarity is defined as moles of solute per cubic decimetre of solution.

Key Concept

Molar Concentration of Hydrated Copper Compounds
Estimated Time:1m 30s
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Topics

Copper: Extraction, Physical and Chemical Properties, and Compounds

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