Sketching titration curves |
The sketching of titration curves is a skill that needs some practice. In order to get the curve correct in a particular case, you have to have in your mind the following points:
Each of these is dependent on the nature of the acid and the base, whether strong or weak. The starting pH will often have been the subject of a calculation in a previous part of the question, or it will have been given in the question itself. You would be expected to start at this value! The final pH can usually be calculated fairly easily since either the acid or the base is in excess by the time the curve has levelled out. Consider the titration of 25.0 cm3 of
0.1 mol dm - 3 HCl solution with
pH = - log {[H+]/mol dm - 3} since you can only take the logarithm of a number, not of a physical quantity.
Similar arguments can be made for titration using weak acids or weak bases; remember that a weak acid/strong base titration will have an endpoint pH around 8, and a strong acid/weak base titration around pH 5.
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© JRG Beavon 2016