Practical investigations
Read our general notes on Risk Assessment
I am trying to determine ethanol content of wine by oxidising with potassium dichromate(VI) and back-titrating with ammonium iron(II) sulphate solution. I need to standardise the ammonium iron(II) sulphate solution by titrating directly with potassium dichromate(VI) solution. I assume this titration does not involve any ethanol solution? Is there any indicator I could use to make the end point clearer? I tried sodium diphenylamine sulphonate made up as suggested using phosphoric acid but it didn’t seem to work. Is it because I am using the oxidised version?
100408
Igloo writes ...
In any case you should persevere with the sodium diphenylamine-4-sulphonate indicator, because it should work, and I know of no better alternative. You are never going to get the same sort of sharp end-point that you get with an iodine-thiosulphate titration, a manganate(VII) titration or with an acid-base titration using phenolphthalein. However, you should be able to achieve an end-point within 1 cm3 or so.
Here are some other ideas:
How old is your sodium diphenylamine-4-sulphonate? Try using more dilute solutions, where the orange/green of the dichromate doesn’t mask out everything.
Incidentally, it doesn’t matter whether you are using the “oxidised” version, as you put it, or not. The colour will change with its environment i.e. your reaction mixture, and whether it’s present in an “oxidising” or a “reducing” solution.
Risk assessment
Before attempting any practical work based on the advice and suggestions on this website, you must do the following. Identify any hazards, assess the risks from these hazards, and then decide appropriate control measures to reduce the risks. You must have these approved by those in authority in your school or college laboratory. Do not rely on what is said on this website.
For further guidance see our tutorial on Risk Assessment.
back to Practical investigations
Rate this page or react
Share your views on this page, 0 ratings so far
updated: 11 April 2008
