Determine the percentage of iron in an iron tablet. LC HL Chemistry 2003 q1

Redox titration involving determining the percentage of iron in an iron tablet using a standard solution of potassium manganate vii. Question taken from leaving certificate higher level chemistry 2003 paper question 1. Calculations performed using first principles.

In this final question 1, there are technically two experiments - even though they are essentially the same. In the first experiment we use a standard solution of ammonium iron ii sulphate to work out the concentration of potassium manganate vii solution. Then in the second part of the experiment, we use this standardised potassium manganate vii solution to work out the concentration of iron in iron tablets. This can be a difficult little calculation and it too hasnt been up in a while from what I remember. Have a look at the front cover of the exam papers and see. Could be a contender also. But the theory will be lovely. The two main points here are when do we use dilute sulphuric acid. The first reason is in the preparation of the iron ii solution whether it be from the tablets or from the ammonium iron ii sulphate. The dilute sulphuric acid is added to prevent the early oxidation of Fe2+ ions to Fe3+ ions by oxygen in the air. The second reason is when additional dilute sulphuric acid is added to the conical flask before the titration is carried out. It is added here to ensure complete reduction of Mn7+ to Mn2+ preventing the formation of the brown specks of the intermediate, Mn4+, manganese dioxide. There is no indicator here as potassium manganate vii acts as it's own indicator, readings taken from the top of the meniscus. The colour change is colourless = first permanent pink tinge. Obviously since we are adding a purple colour it will go more purple, so don't put these in the wrong order.

Exam Paper: https://www.examinations.ie/tmp/15873...