Transition elements
Read our general notes on Risk Assessment
I’m doing my Adv. Higher project on the iron content of iron tablets. I need to standardise my potassium dichromate solution but cannot find any methods for doing so.
181209
Igloo writes ...
The usual procedure for standardising a solution of potassium dichromate(VI) involves the use of ammonium iron(II) sulphate, which is a primary standard and can be obtained in a very high state of purity.
First you need to make up a standard solution of ammonium iron(II) sulphate in dilute sulphuric acid, perhaps using a 250 cm3 volumetric flask and a known mass of the solid. You would then titrate portions of known volume of the potassium dichromate(VI) solution with the solution of ammonium iron(II) sulphate, using a redox indicator such as sodium diphenylamine sulphonate.
Knowledge of the concentration of the ammonium iron(II) sulphate and the titration reading will enable you to calculate the number of moles of Fe2+ ions used.
Use of the equation:
6Fe2+(aq) + Cr2O72- (aq) + 14H+ (aq) ----> 6Fe3+ (aq) + 2Cr3+ (aq) + 7H2O(l)
will enable you to deduce the number of dichromate(VI) ions which were present in the flask.
Knowing the volume of the potassium dichromate(VI) solution used you can then deduce its accurate concentration in mol dm-3.
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.
Rate this page or react
Share your views on this page, 0 ratings so far
updated: 19 December 2009
