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This question is about the extraction of metals - AQA - GCSE Chemistry - Question 3 - 2021 - Paper 1

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This question is about the extraction of metals. Element R is extracted from its oxide by reduction with hydrogen. The equation for the reaction is: $$3H_2 + RO_3... show full transcript

Worked Solution & Example Answer:This question is about the extraction of metals - AQA - GCSE Chemistry - Question 3 - 2021 - Paper 1

Step 1

03.1 The sum of the relative formula masses (M_f) of the reactants (3H_2 + RO_3) is 150 Calculate the relative atomic mass (A_r) of R.

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Answer

To solve for the relative atomic mass of element R, we start with the equation:

Mf(3H2+RO3)=3Mf(H2)+Mf(RO3)=150M_f (3H_2 + RO_3) = 3M_f(H_2) + M_f(RO_3) = 150

The molar mass of hydrogen is given as 1, so:

Mf(H2)=2×1=2M_f(H_2) = 2 \times 1 = 2

Therefore,

3Mf(H2)=3×2=63M_f(H_2) = 3 \times 2 = 6

Hence,

6+Mf(RO3)=1506 + M_f(RO_3) = 150

Solving for Mf(RO3)M_f(RO_3) gives:

Mf(RO3)=150−6=144M_f(RO_3) = 150 - 6 = 144

Now, The relative formula mass of RO3RO_3 is the sum of the atomic mass of R and the contributions from the three oxygen atoms:

Mf(RO3)=Ar(R)+3×16=144M_f(RO_3) = A_r(R) + 3 \times 16 = 144

This simplifies to:

Ar(R)+48=144A_r(R) + 48 = 144

Therefore,

Ar(R)=144−48=96A_r(R) = 144 - 48 = 96

Step 2

03.2 Identify element R.

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Answer

Based on the relative atomic mass calculated in the previous step (A_r(R) = 96), we can refer to the periodic table. The element with an atomic mass close to 96 is molybdenum (Mo). Therefore, element R is molybdenum.

Step 3

03.3 Calculate the percentage atom economy for extracting tin in this reaction.

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Answer

To calculate the percentage atom economy, we first need to find the total molar mass of reactants and the desired product.

From the equation: SnO2+C→Sn+CO2SnO_2 + C \rightarrow Sn + CO_2

The molar masses are as follows:

  • Molar mass of SnO2 = 119 (Sn) + 32 (O2) = 151 g/mol
  • Molar mass of C = 12 g/mol
  • Total mass of reactants = 151 + 12 = 163 g/mol

The total mass of the desired product (tin) produced is the molar mass of Sn, which is 119 g/mol.

Now, the percentage atom economy is calculated using the formula:

Percentage Atom Economy=(Mass of Desired ProductTotal Mass of Reactants)×100 \text{Percentage Atom Economy} = \left( \frac{\text{Mass of Desired Product}}{\text{Total Mass of Reactants}} \right) \times 100

Substituting in the values:

Percentage Atom Economy=(119163)×100≈73% \text{Percentage Atom Economy} = \left( \frac{119}{163} \right) \times 100 \approx 73\%

Step 4

03.4 Evaluate the three possible methods to extract tungsten from tungsten oxide.

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Answer

The three methods to extract tungsten are:

  1. Carbon:

    • Advantages: Low relative cost of reactant.
    • Disadvantages: Produces tungsten carbide, which complicates separation processes.

  2. Hydrogen:

    • Advantages: High relative effectiveness, producing pure tungsten solid.
    • Disadvantages: High cost of the hydrogen reactant, although it produces useful water vapor.

  3. Iron:

    • Advantages: Low relative cost of reactant.
    • Disadvantages: Produces iron oxide as a by-product, necessitating additional separation steps.

In summary, carbon is the cheapest option, but it involves additional separation processes due to by-products. Hydrogen, while costly, may offer purer tungsten. Iron presents a balance between cost and product purity but also has associated separation challenges. Overall, the choice of method depends on the balance of cost, efficiency, and product purity.

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