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

When excess copper turnings are reacted with dilute trioxonitrate(V) acid (HNO3\text{HNO}_3), 1.12 dm31.12\text{ dm}^3 of nitrogen(II) oxide (NO\text{NO}) gas, measured at STP, is evolved. What mass of copper metal was oxidized during this reaction?

(Molar mass of Cu=64 g mol−1, molar volume of gas at STP=22.4 dm3 mol−1)(\text{Molar mass of Cu} = 64\text{ g mol}^{-1},\text{ molar volume of gas at STP} = 22.4\text{ dm}^3\text{ mol}^{-1})

  1. 4.8 g4.8\text{ g}Answer
  2. B
    3.2 g3.2\text{ g}
  3. C
    1.6 g1.6\text{ g}
  4. D
    2.1 g2.1\text{ g}

Answer

4.8 g4.8\text{ g} of copper metal was oxidized.
The option specifying 4.8 g4.8\text{ g} is correct because the balanced chemical reaction of copper turnings with dilute trioxonitrate(V) acid is 3Cu+8HNO3→3Cu(NO3)2+2NO+4H2O3\text{Cu} + 8\text{HNO}_3 \rightarrow 3\text{Cu(NO}_3)_2 + 2\text{NO} + 4\text{H}_2\text{O}. Converting 1.12 dm31.12\text{ dm}^3 of NO\text{NO} at STP gives 0.05 mol0.05\text{ mol}. Multiplying by the stoichiometric ratio 32\frac{3}{2} gives 0.075 mol0.075\text{ mol} of Cu\text{Cu}, which equals 0.075×64=4.8 g0.075 \times 64 = 4.8\text{ g}.

Step-by-Step Solution

1
Write the balanced chemical equation for the reaction of copper with dilute trioxonitrate(V) acid.
3Cu(s)+8HNO3(aq)→3Cu(NO3)2(aq)+2NO(g)+4H2O(l)3\text{Cu}(s) + 8\text{HNO}_3(aq) \rightarrow 3\text{Cu(NO}_3)_2(aq) + 2\text{NO}(g) + 4\text{H}_2\text{O}(l)
Dilute HNO3\text{HNO}_3 acts as an oxidizing agent, reducing to nitrogen(II) oxide (NO\text{NO}) gas rather than hydrogen gas.
2
Calculate the moles of nitrogen(II) oxide (NO\text{NO}) gas produced at STP.
Moles of NO=1.12 dm322.4 dm3 mol−1=0.05 mol\text{Moles of NO} = \frac{1.12\text{ dm}^3}{22.4\text{ dm}^3\text{ mol}^{-1}} = 0.05\text{ mol}
At STP, one mole of any ideal gas occupies 22.4 dm322.4\text{ dm}^3.
3
Use the mole ratio to determine moles of copper oxidized.
Moles of Cu=0.05 mol NO×(3 mol Cu2 mol NO)=0.075 mol Cu\text{Moles of Cu} = 0.05\text{ mol NO} \times \left(\frac{3\text{ mol Cu}}{2\text{ mol NO}}\right) = 0.075\text{ mol Cu}
The stoichiometric ratio between Cu\text{Cu} and NO\text{NO} is 3:2.
4
Convert moles of copper to mass in grams.
Mass of Cu=0.075 mol×64 g mol−1=4.8 g\text{Mass of Cu} = 0.075\text{ mol} \times 64\text{ g mol}^{-1} = 4.8\text{ g}
Mass is calculated by multiplying the number of moles by the molar mass.

Key Concept

Stoichiometry of redox reactions involving transition metals and oxidizing acids
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Topics

Copper: Extraction, Physical and Chemical Properties, and Compounds

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