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Difficulty: Very hardCopper: Extraction, Physical and Chemical Properties, and Compounds
During the smelting stage of copper extraction, copper pyrites (CuFeS2CuFeS_2) is roasted in air according to the following balanced equation:
2CuFeS2(s)+4O2(g)→Cu2S(s)+2FeO(s)+3SO2(g)2CuFeS_{2(s)} + 4O_{2(g)} \rightarrow Cu_2S_{(s)} + 2FeO_{(s)} + 3SO_{2(g)}
If 0.50 mole0.50\text{ mole} of CuFeS2CuFeS_2 is reacted with 0.80 mole0.80\text{ mole} of O2O_2, which reagent is limiting, what volume of SO2SO_2 gas is produced at STP, and what is the oxidation state of iron in the resulting FeOFeO?
[Molar volume of gas at STP = 22.4 dm3 mol−122.4\text{ dm}^3\text{ mol}^{-1}]
  1. O2O_2 is limiting; 13.44 dm313.44\text{ dm}^3 of SO2SO_2; iron oxidation state is +2+2Answer
  2. B
    CuFeS2CuFeS_2 is limiting; 16.80 dm316.80\text{ dm}^3 of SO2SO_2; iron oxidation state is +2+2
  3. C
    O2O_2 is limiting; 14.40 dm314.40\text{ dm}^3 of SO2SO_2; iron oxidation state is +2+2
  4. D
    O2O_2 is limiting; 13.44 dm313.44\text{ dm}^3 of SO2SO_2; iron oxidation state is 00

Answer

Oxygen gas (O2O_2) is the limiting reactant, yielding 13.44 dm313.44\text{ dm}^3 of SO2SO_2 gas at STP, and iron in FeOFeO has an oxidation state of +2+2.
The correct answer identifies oxygen gas (O2O_2) as the limiting reactant because 0.50 mole0.50\text{ mole} of CuFeS2CuFeS_2 requires 1.00 mole1.00\text{ mole} of O2O_2 for complete reaction, but only 0.80 mole0.80\text{ mole} is provided. Utilizing O2O_2 to calculate product yield gives 0.60 mole0.60\text{ mole} of SO2SO_2, which translates to 13.44 dm313.44\text{ dm}^3 at STP (0.60×22.40.60 \times 22.4). Iron in FeOFeO carries an oxidation state of +2+2.

Step-by-Step Solution

1
Determine the limiting reactant by comparing the mole ratio of available reactants to stoichiometric coefficients
From the balanced equation, 2 moles2\text{ moles} of CuFeS2CuFeS_2 require 4 moles4\text{ moles} of O2O_2 (ratio 1:21:2). 0.50 mole0.50\text{ mole} of CuFeS2CuFeS_2 requires 1.00 mole1.00\text{ mole} of O2O_2. Since only 0.80 mole0.80\text{ mole} of O2O_2 is available, O2O_2 is the limiting reactant.
The reaction extent is governed entirely by the reactant that is fully consumed first.
2
Calculate the moles of SO2SO_2 produced using the limiting reactant
According to the stoichiometric ratio, 4 moles4\text{ moles} of O2O_2 produce 3 moles3\text{ moles} of SO2SO_2. Therefore, 0.80 mole0.80\text{ mole} of O2O_2 produces 0.80×34=0.60 mole0.80 \times \frac{3}{4} = 0.60\text{ mole} of SO2SO_2.
The yield of product depends directly on the moles of the limiting reactant.
3
Convert moles of SO2SO_2 gas to volume at STP
Volume of SO2=0.60 mole×22.4 dm3 mol−1=13.44 dm3SO_2 = 0.60\text{ mole} \times 22.4\text{ dm}^3\text{ mol}^{-1} = 13.44\text{ dm}^3.
At STP, one mole of any ideal gas occupies 22.4 dm322.4\text{ dm}^3.
4
Determine the oxidation state of iron in FeOFeO
Oxygen has an oxidation state of −2-2. For neutral FeOFeO, Fe+(−2)=0⇒Fe=+2\text{Fe} + (-2) = 0 \Rightarrow \text{Fe} = +2.
The sum of oxidation states in a neutral compound equals zero.

Key Concept

Copper extraction roasting reaction stoichiometry and limiting reactant calculations
Estimated Time:2m 30s
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Topics

Copper: Extraction, Physical and Chemical Properties, and Compounds

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