This question is about displacement reactions - AQA - GCSE Chemistry - Question 6 - 2020 - Paper 1

To determine the limiting reactant, we first calculate the moles of each reactant.

1. Calculate Molar Mass of Iron(III) Oxide (Fe2O3):

   $M_{Fe2O3} = 2 imes Ar_{Fe} + 3 imes Ar_{O} = 2 imes 56 + 3 imes 16 = 160 ext{ g/mol}$

2. Calculate Moles of Iron(III) Oxide:

   $ext{Moles of Fe2O3} = \frac{3.00 ext{ kg}}{160 ext{ g/mol}} = 18.75 ext{ moles}$

3. Calculate Moles of Aluminium Needed:

   One mole of ext{Fe2O3} requires 2 moles of aluminium. Therefore, for 18.75 moles:

   $ext{Moles of Al needed} = 18.75 ext{ moles} imes 2 = 37.5 ext{ moles}$

4. Calculate Moles of Aluminium Available:

   $ext{Moles of Al} = \frac{1.00 ext{ kg}}{27 ext{ g/mol}} = 37.037 ext{ moles}$

5. Conclusion: Since 37.5 moles of Al are needed for the reaction and only 37.037 moles are available, aluminium is the limiting reactant.

The balanced ionic equation for the reaction of magnesium and zinc sulfate is:

$Mg(s) + Zn^{2+}(aq) → Mg^{2+}(aq) + Zn(s)$

In this reaction, magnesium atoms are oxidized because they lose electrons, transforming from neutral magnesium to magnesium ions (${Mg^{2+}}$). Conversely, the zinc ions (${Zn^{2+}}$) gain electrons and are reduced to form solid zinc. This simultaneous loss of electrons by magnesium and gain by zinc highlights the concept of oxidation-reduction (redox) reactions.