Determination Of Iron In Vitamin Tablets

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Analysis of iron tablets Titration Titration experiments allow the concentration of a solution to be determined. The solution with the known concentration is called the standard solution or titrant. The solution with the unknown concentration is called the analyte. In acid-alkali titrations an indicator such as phenolphthalein is needed to see the end-point. However, the redox reaction between manganate(VII) ions and iron(II) ions is self-indicating. Before the end-point the purple colour disappears in the reaction but this cannot happen after the end-point, so the end-point is when the first permanent pink colour appears. It is important that the sample is acidified, and this must be achieved using sulphuric acid (hydrochloric acid interferes with the titration). It is important that the volumes are measured precisely. A transfer pipette is used to transfer liquid to the conical flask, and a burette is used to transfer the other liquid. The graduations on the burette show how much liquid has been added, not how much is left in the burette. These are typical precautions for an accurate titration: • • • make sure that the burette is stable and vertical remove the funnel from the top before starting a run take readings at the level of the meniscus: for dark liquids measure from the top of the meniscus, but for colourless liquids measure from the bottom of the meniscus use a white tile below the conical flask to see the colour change more clearly swirl the conical flask continually while adding from the burette reduce the flow to drop-wise near the end-point and rinse down the inside of the conical flask using de-ionised water from a wash bottle repeat until at least two concordant titres are obtained, i.e. results with 0.10 cm3 of each other. • • • • © Harcourt Education Ltd 2005 This document may have been altered from the original on the CD-ROM.

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