Chemical quantities (AS)
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I am required to plan an investigation in chemistry, and it involves a titration experiment ... but I am so confused .... The measurements we have been given are that we have to neutralise a sample of sulphuric acid that has a concentration of 0.5–0.15 mol dm–3 using an unknown volume/concentration of sodium carbonate (solid). However, I do not understand how I can perform the titration using a solid. I am assuming I would have to make up a concentration of sodium carbonate and water ... but how do I work out what concentration to make the sample? ... and do I put this solution in the burette or in the conical flask? ..... and what calculations should be done afterwards? ... as you can see I am very very confused and would very much appreciate a little assistance, if you can understand my question that is ....
Ulex says ... OK don’t panic (unless, of course, you already have!) The steps are as follows.
1. Write the equation for the reaction – sodium sulphate, carbon dioxide and water are the products.
2. Observe that, in the equation, one mole of sulphuric acid reacts with one mole of sodium carbonate. If it doesn’t, you have a wrong formula for sodium carbonate, sodium sulphate or both!
3. Your sulphuric acid has a concentration of about 0.3M – you are going to find out what its concentration really is, reasonably accurately. According to the equation you will therefore want a sodium carbonate solution which is about the same concentration. So you need 0.3 moles to make a cubic decimetre of solution, but as you don’t really need as much as that, weigh out 0.03 moles, dissolve it in water, and make up to 100 cm3 instead. Use a graduated flask for this and specify pure water. Mix well.
4. Put the acid in the burette and titrate 10.0 cm3 portions (pipette) of the sodium carbonate solution with the acid using methyl orange as indicator (indicator choice is an A2 topic so you can’t be expected to know this at this stage). Do a rough titration and at least two accurate ones – they should agree to within 0.1 cm3.
5. Do the calculation in much the same way as the exercise in the text – see p 84 of the Nuffield Chemistry Students’ Book.
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updated: 29 February 2004
