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This question is about zinc and magnesium - AQA - GCSE Chemistry - Question 4 - 2014 - Paper 1
Question 4
This question is about zinc and magnesium. Zinc is produced by electrolysis of molten zinc chloride, as shown in Figure 4. Figure 4 Negative electrode Positiv... show full transcript
Worked Solution & Example Answer:This question is about zinc and magnesium - AQA - GCSE Chemistry - Question 4 - 2014 - Paper 1
Step 1
Step 2
Describe what happens at the negative electrode.
Answer
At the negative electrode, zinc ions gain electrons, which is referred to as reduction. The reaction can be summarized as follows:
- Zinc ions (Zn²⁺) move towards the negative electrode.
- Electrons from the electrode are taken up by the zinc ions, converting them to neutral zinc atoms.
- Consequently, metallic zinc is formed at the negative electrode.
Step 3
Step 4
How can you tell from the equation that the reaction is done at a high temperature?
Answer
The reaction is typically at a high temperature because magnesium, which is a gas in this reaction, is produced. This indicates that the substances must reach a temperature high enough to move from solid to gas form, which is only feasible at elevated temperatures.
Step 5
Step 6
Calculate the mass of magnesium oxide needed to produce 1.2 tonnes of magnesium.
Answer
To calculate the mass of magnesium oxide needed, we use the stoichiometry of the reaction. According to the balanced chemical equation:
ightarrow 2 Mg(g)$$ Since the relative atomic mass (Aᵣ) of Mg is 24, we can derive the mass of MgO needed. 1.2 tonnes of Mg = 1200 kg. 2 mol of MgO produces 2 mol of Mg, hence: $$ ext{Mass of MgO} = rac{1.2 ext{ tonnes}}{2 ext{ moles}} imes 2 imes 40 ext{ (molar mass of MgO)} = 1.2 imes 40 ext{ (to convert tonnes to kg)} = 40 kg$$.Step 7
Calculate the percentage yield.
Answer
To calculate the percentage yield, we use the formula:
ext{Percentage yield} = rac{ ext{actual yield}}{ ext{theoretical yield}} imes 100
Here, the actual yield is 0.9 tonnes, and the theoretical yield is 1.2 tonnes.
ext{Percentage yield} = rac{0.9}{1.2} imes 100 = 75 ext{%}
Step 8
Give one reason why the calculated yield of magnesium might not be obtained.
Answer
One possible reason is that there may have been some losses during the reaction process. For instance, reactants could escape during the reaction, or some reactants may react in ways that were not anticipated, producing impurities or by-products.