This question is about silicon and compounds of silicon - AQA - GCSE Chemistry - Question 7 - 2022 - Paper 1

More energy is required to obtain aluminium compared to carbon. Aluminium is usually extracted from aluminium oxide through electrolysis, which is a more energy-intensive process.

Both products, silicon and magnesium oxide, are solid, making it challenging to separate them after the reaction.

The molar mass of SiO₂ is calculated as:

$M_{f} \text{ of SiO}_2 = 28 + (2 \times 16) = 60 \text{ g/mol}$

For 1.2 kg of SiO₂, the number of moles is:

$\text{moles of SiO}_2 = \frac{1200 \text{ g}}{60 \text{ g/mol}} = 20 \text{ moles}$

The number of moles of Mg needed is twice that of SiO₂:

$\text{moles of Mg} = 20 \times 2 = 40 \text{ moles}$

The mass of magnesium required:

$\text{mass of Mg} = \text{moles} \times \text{molar mass} = 40 \times 24 = 960 \text{ g}$

The outer shell electrons of SiH₄ consist of 4 hydrogen atoms and 1 silicon atom. Each hydrogen atom contributes 1 electron while silicon has 4 electrons to share with the hydrogens.

The volume of oxygen for 30 cm³ of SiH₄ is:

$\text{Volume of oxygen} = 30 \text{ cm}^3 \times 7 = 210 \text{ cm}^3$

The volume of excess oxygen after reaction:

$\text{Volume of excess oxygen} = 150 \text{ cm}^3 - 210 \text{ cm}^3 = -60 \text{ cm}^3$

Since this indicates that oxygen is not in excess, we will adjust:

Total volume of gases after the reaction:

$\text{Volume of gases} = 3 \cdot \text{moles of water} + \text{gases from SiO}_2 = 3 \times 0.001875 + 30 \text{ cm}^3 = 135 \text{ cm}^3$