Analysing a sample for H2S04

[oz82]

Lets say you collected a sample and you knew it had Aluminium Sulphate and Sulphuric Acid in it. You try to determine the amount of Sulphuric Acid and get a surprisingly high result. The results could be overstated because the barium perchlorate titration you used is specific to sulfate and cannot differentiate between H2SO4 or aluminium sulfate. Does anybody know of an analysis that would show the difference??

Ta

[woelen]

Measure the pH, e.g. by titrating with a solution of NaOH of known concentration. Especially if the concentration of acid is high, this gives a good and accurate result. Use an indicator, which changes color, when pH goes from 4 to 5 or somewhere around that. Using such an indicator, you take into account the somewhat acidic properties of Al(3+)-ions.

[John Cuthber]

You could measure the aluminium and work out how much sulphate the aluminium sulphate contributed.

A titration using a pH meter as the "indicator" would, I think, give breakpoints corresponding to the titre of H2SO4, HSO4 and Al+++ so that would give quite a lot of information.

[Crooked Mick]

One of the standard methods is to titrate with borax, sodium tetraborate decahydrate. This is a "secondary" standard and a sufficiently accurate solution for most purposes can be made by dissolving a weighed amount in water after GENTLE drying. However I do not know whether the presence of a lot of Al2(SO4)3 would affect the end point a great deal. Indicator was, if memory serves methyl red in presence of methylene blue. Colour change was purple -green, more or less. See standard methods for determination of sulphur in coal by the high temperature tube furnace method. Can't be more specific, it's 18 years since I've done this.