Chemical amounts (A2)
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I am doing a mock practical assessment. The title is 'Determining the solubility of a solid, weak acid by titration'. I am asked to design an experiment to measure the solubility of ethanedioic acid in water at room temp, by preparing a saturated solution and then titrating it with alkali. Preliminary experiments indicate that between 8 and 10 g of ethanedioic acid dissolve in 100 cm3 of water. I really don't know how to start. I hope that you could possibly shed some light on the situation.
Ulex says
This one was set as part of an exam question on the old syllabus, when experimental design was part of the written exam rather than part of coursework! At the time it caused a lot of confusion so you are not alone. However, the answer is almost there in the question.
The first thing to do is to make a saturated solution. Take some pure water (you decide how much but it doesn’t matter so long as you get enough solution to work with). Put it in a suitable piece of glassware (you decide what and how big) and add solid ethanedioic acid (add more than the suggested amounts in the question – you decide). Shake or stir, cover the container and leave for 24 hours so that the solution saturates. There should be some solid left. Filter. You now have your saturated solution.
Given the rough concentration of a saturated solution you can work out a suitable concentration of the strong base that you are going to use to titrate this weak acid. Bear in mind that 2 mol of a base such as NaOH or KOH reacts with 1 mol of ethanedioic acid.
You need to choose a suitable indicator for a titration of a weak acid with a strong base.
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Risk assessment
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updated: 17 December 2003
