Some people take iron tablets as a dietary supplement - Scottish Highers Chemistry - Question 7 - 2017

The reaction with permanganate is self-indicating since the color changes from purple to colorless as it reacts with the iron(II) ions.

It is essential to perform the titration under acidic conditions to ensure that the iron(II) ions are fully oxidized to iron(III), allowing the reaction with permanganate to proceed correctly.

The volume of 14.55 cm³ is taken as it represents the mean of the three titrations, which gives a more accurate representation than the individual results, minimizing experimental errors.

Using the titration results, the average volume of permanganate used is 14.55 cm³, which is equivalent to 0.01455 dm³. The concentration of permanganate is 0.020 mol dm⁻³.

The reaction is:

$5 ext{Fe}^{2+} + ext{MnO}_4^{-} + 8 ext{H}^+ \rightarrow 5 ext{Fe}^{3+} + ext{Mn}^{2+} + 4 ext{H}_2 ext{O}$

Using the stoichiometric relationship:

$n_{ ext{MnO}_4^-} = C_{ ext{MnO}_4^-} imes V_{ ext{MnO}_4^-} = 0.020 imes 0.01455 = 0.000291$

From the balanced equation, the moles of Fe²⁺ is:

$n_{ ext{Fe}^{2+}} = 5 imes n_{ ext{MnO}_4^-} = 5 imes 0.000291 = 0.001455$

The concentration of Fe²⁺ in 25.0 cm³ is:

C_{ ext{Fe}^{2+}} = rac{n_{ ext{Fe}^{2+}}}{V_{ ext{Fe}^{2+}}} = rac{0.001455}{0.025} = 0.0582 ext{ mol l}^{-1}

A standard solution is a solution whose concentration is known exactly, usually prepared by accurately dissolving a measured mass of solute in a specific volume of solvent.

A pipette would be suitable for accurately measuring 25.0 cm³ samples of the iron tablet solution.

The total moles of iron(II) in five tablets is 0.00126 moles. Therefore, the moles of iron in one tablet is:

rac{0.00126}{5} = 0.000252 ext{ moles}

The molar mass of iron (Fe) is approximately 56 g/mol. Thus, the mass of iron in one tablet is:

$0.000252 imes 56 ext{ g} = 0.014112 ext{ g} = 14.112 ext{ mg}$

If 100 g of cereal contains 12.0 mg of iron, then 30 g provides:

rac{12.0 ext{ mg}}{100 ext{ g}} imes 30 ext{ g} = 3.6 ext{ mg}

The recommended daily amount of iron is 14.8 mg. Therefore, the percentage provided by the 30 g serving is:

rac{3.6 ext{ mg}}{14.8 ext{ mg}} imes 100 = 24.32 ext{ \\%}