Some people take iron tablets as a dietary supplement - Scottish Highers Chemistry - Question 7 - 2023

The reaction is self-indicating because potassium permanganate acts as its own indicator by changing color.

Acidic conditions provide the necessary hydrogen ions (H⁺) for the redox reaction to proceed, which facilitates the conversion of Fe²⁺ to Fe³⁺.

The volume of 14.55 cm³ is taken as the average of the titration results, providing a more reliable value than any single measurement.

For the reaction given:

$5Fe^{2+}(aq) + 8H^{+}(aq) + MnO_{4}^{-}(aq) \rightarrow 5Fe^{3+}(aq) + Mn^{2+}(aq) + 4H_{2}O (l)$

Using the average volume of permanganate:

$\text{Moles of } MnO_4^{-} = 0.02 \times \frac{14.55}{1000} = 0.000291$

The total moles of Fe²⁺ that reacted are:

$\text{Moles of } Fe^{2+} = 5 \times 0.000291 = 0.001455$

Using the volumetric relationship, the concentration of Fe²⁺ in the original solution:

$\text{C}_{Fe^{2+}} = \frac{0.001455}{0.025} = 0.0582 \text{ mol l}^{-1}$

A standard solution is a solution of accurately known concentration, used as a reference in titrations.

A pipette is an appropriate piece of apparatus that can be used to measure 25.0 cm³ samples.

Given that five iron tablets contain 0.00126 moles of iron(II) ions:

Molar mass of iron = 55.85 g/mol

Total mass of iron in five tablets:

$\text{mass} = 0.00126 \text{ mol} \times 55.85 \text{ g/mol} = 0.0704 \text{ g} = 70.4 \text{ mg}$

Average mass of iron per tablet:

$\text{Average mass} = \frac{70.4 \text{ mg}}{5} = 14.08 \text{ mg}$

The daily recommended intake for an adult female is 14.8 mg of iron. The cereal provides:

$\text{Iron from } 30 ext{ g} = \frac{30}{100} \times 12.0 = 3.6 ext{ mg}$

Percentage of daily intake:

$\text{Percentage} = \frac{3.6 ext{ mg}}{14.8 ext{ mg}} \times 100 \approx 24.32 \%$