Copper(II) sulfate crystals, CuSO4•5H2O, can be made by heating copper(ll) oxide with dilute sulfuric acid and then crystallising the solution formed. a) Calculate the maximum mass of crystals that could be made from 4.00g of copper(II) oxide using an excess of sulfuric acid.
CuO(s) + H2SO4(aq) → CuSO4(aq) + H2O(l)
CuSO4(aq) + 5H2O(l) → CuSO4•5H2O(s) b) If the actual mass of copper(II) sulfate collected at the end of the experiment was 11.25g, calculate the percentage yield.
(Ar: H = 1, 0 = 16, S = 32, Cu = 63.5)
Answers
Answer:
Add 20 cm3 of the 0.5 M sulfuric acid to the 100 cm3 beaker. Heat carefully on the tripod with a gentle blue flame until nearly boiling. (Be very careful not to knock the tripod while the beaker is on it. Consider clamping the beaker.)
SHOW FULLSCREEN
A diagram showing the apparatus required for heating copper(II) oxide and dilute sulfuric acid
Source: Royal Society of Chemistry
Apparatus for heating copper(II) oxide and dilute sulfuric acid.
When the acid is hot enough (just before it starts to boil), use a spatula to add small portions of copper(II) oxide to the beaker. Stir the mixture gently for up to half a minute after each addition. (When adding the solid to the beaker, take care to avoid knocking the beaker.)
When all the copper(II) oxide has been added, continue to heat gently for 1–2 minutes to ensure reaction is complete. Then turn out the Bunsen burner. It may be wise to check (using pH or litmus paper) that no acid remains. If the acid has not been hot enough, excess acid can co-exist with copper oxide. (Boiling off the water so that the copper sulfate appears and then decomposes with excessive heating is unsafe. The sulfur dioxide gases are toxic and can cause breathing difficulties.)
Allow the beaker to cool slightly while you set up Stage 2.
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A diagram showing the apparatus required to filter a heated copper(II) sulfate solution, removing unreacted copper(II) oxide
Source: Royal Society of Chemistry
Apparatus required to filter a heated copper(II) sulfate solution, removing unreacted copper(II) oxide.
a) 8.05 g of CuSO₄
b) 89.42 %
Explanation:
a) CuO(s) + H₂SO₄(aq) → CuSO₄(aq) + H₂O(l)
Molecular weight of CuO = 79 g, Mole. wt. of CuSO₄ = 159 g,
When 79 g of CuO reacts with H₂SO₄ 159 g of CuSO₄ is formed.
∴ 4 g of CuO gives = 159/79 × 4
= 8.05 g of CuSO₄
b) Theoretical yield and % yield :
Theoretical yield:
159.6 g of CuSO₄ → 249.5 g of CuSO₄.5H₂O
8.05 g = 249.5 × 8.05/159.6
= 12.58 g
Percentage yield = Weight of the product/Theoretical yield × 100
= 11.25/12.58 × 100
= 89.42 %