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Module 1: Practical chemistry for exams›PAG 12.1 - Investigating iron tablets

PAG 12.1 - Investigating iron tablets

An overview of PAG 12.1 - Investigating iron tablets

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In OCR Chemistry Required Practical 12 (PAG 12.1), the percentage by mass of iron compound within a commercial iron tablet is determined.

This experiment is based around a redox titration using potassium manganate (VII) and its oxidation of to in acid solution. This equation is given below:

In OCR PAG 12.1: Investigating iron tablets, there are several important safety requirements to be aware of (beyond normal lab practice such as wearing goggles).

Use a pipette filler – never pipette by mouth.
Immediately clean up any spills of acid.

Experimental method for OCR Chemistry Required Practical 12 (PAG 12.1)

The image illustrates an experimental method for titration in five steps. Step 1: 'Prepare the iron tablets' shows crushing tablets in a mortar, transferring powder to a weighing boat, and then to a beaker. Step 2: 'Iron tablet solution' involves adding 100 cm³ of 1.0 mol dm⁻³ sulfuric acid to dissolve iron, filtering into a 250 cm³ volumetric flask, washing with sulfuric acid, and making up to the mark with distilled water, followed by inversion. Step 3: 'Prepare the reactants' shows pipetting 25.0 cm³ of iron solution into a conical flask, then filling a burette with 0.005 mol dm⁻³ potassium manganate(VII) solution to the 0.00 cm³ mark. Step 4: 'Draw up a titration results table' advises recording all data to 2 decimal places in a table with columns for trial, initial volume, final volume, titre used, mean titre, and concordant titres. Step 5: 'Titrate the potassium manganate(VII) solution' involves adding the purple solution to a conical flask with swirling until a slight pink color remains, recording the final volume, and repeating for concordant results.

It is crucial to use clean and dry glassware when performing analytical tests.

Five test tubes arranged in a row, with varying heights and shapes.

Do

Ensure all glassware is clean and dry before use to avoid contamination and ensure accurate results.

A test tube with a white body and brownish stains or markings on its surface.

Don't

Reuse glassware that has not been properly cleaned and dried, as this could lead to inaccurate readings or unintended chemical reactions.

Calculate the mean titre from concordant results (within 0.1cm³) and calculate the moles of using:

Calculate the moles of using the 1:5 ratio from the balanced equation. Then calculate the mass of iron in one tablet using:

Use the result to calculate the mass of iron(II) sulfate, or other main ingredient, and compare this with the value stated on the packaging.