Some people take iron tablets as a dietary supplement - Scottish Highers Chemistry - Question 7 - 2017
Question 7
Some people take iron tablets as a dietary supplement. Iron tablets may contain iron(II) sulfate.
(a) A student was investigating the iron(II) content of iron table... show full transcript
Worked Solution & Example Answer:Some people take iron tablets as a dietary supplement - Scottish Highers Chemistry - Question 7 - 2017
Step 1
Describe how 'transfer quantitatively' is carried out in practice.
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Answer
To transfer quantitatively, the student should first rinse the beaker containing the dissolved iron tablets with distilled water to ensure all of the solution is washed into the volumetric flask. Once rinsed, the entire contents should be poured carefully into the volumetric flask. Any residual washings should also be transferred to ensure that the entire solution is included.
Step 2
(i) Suggest why it is not necessary to add an indicator to this titration.
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Answer
The reaction is self-indicating. Permanganate (MnO₄⁻) provides a color change from purple to colorless as it is reduced, making it easy to determine the endpoint without the need for a separate indicator.
Step 3
(ii) Suggest why the titration must be carried out under acidic conditions.
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The titration must be conducted under acidic conditions to provide H⁺ ions necessary for the reduction of permanganate ions (MnO₄⁻) to manganese ions (Mn²⁺) during the reaction.
Step 4
(iii)(A) State why the volume of permanganate used in the calculation was taken to be 14.55 cm³.
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The volume of 14.55 cm³ was taken as it represents the mean value of the three trials, providing a more reliable average than any individual reading.
Step 5
(iii)(B) Calculate the concentration, in mol l⁻¹, of iron(II) ions in the iron tablet solution.
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Answer
First, calculate the moles of MnO₄⁻ used in the titration:
(iii)(C) State what is meant by the term standard solution.
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A standard solution is a solution of accurately known concentration, which is commonly used in titrations to determine the concentration of another solution.
Step 7
(iii)(D) Name an appropriate piece of apparatus which could be used to measure 25.0 cm³ samples of iron tablet solution.
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A graduated pipette could be used to accurately measure 25.0 cm³ samples of the iron tablet solution.
Step 8
Calculate the average mass of iron present in one tablet.
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Answer
Given that five iron tablets contain 0.00126 moles of Fe²⁺, the mass of iron in total is:
Mass = Moles × Molar mass = 0.00126 × 55.85 ext{ g/mol} = 0.0704 ext{ g} = 70.4 ext{ mg}.
To find the average mass per tablet, divide by 5:
Average mass per tablet = rac{70.4 ext{ mg}}{5} = 14.08 ext{ mg}.
Step 9
Calculate the percentage of the recommended daily amount of iron provided for an adult female by a 30 g serving.
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The recommended amount of iron per day is 14.8 mg. A 100 g serving of cereal contains 12.0 mg of iron, so a 30 g serving contains:
Iron in 30 g = rac{12.0 ext{ mg}}{100 ext{ g}} × 30 ext{ g} = 3.6 ext{ mg}.
Therefore, the percentage of the daily recommended amount is:
