Report of chemistry experiment on redox titration
Name: Beverly Wong 6S (26)
An analysis of iron tables
To find out the actual percentage of iron (Ⅱ) ions are in a particular brand of iron tables and compare the result with the quantity claimed by the producer.
2. Introduction of the experiment
Iron tables usually contain iron (Ⅱ) sulphate which is soluble in water. Assuming all the iron in the tables is in the form of iron (Ⅱ), Fe2+. The amount of iron can be estimated by titrated iron (Ⅱ), Fe2+ (aq) against potassium permanganate, KMnO4. In the titration, Fe2+ ions react with MnO4- ions and H+ ions according to the following equation:
MnO4- (aq) + 8H+ (aq) + 5Fe2+ (aq) ( Mn2+ (aq) + 4H2O(1) +5Fe3+ (aq)
MnO4- ion is purple, Fe2+ ion is green, Fe3+ ion is brown and Mn2+ ion is colourless. MnO4- ion has a very deep purple colour when it reacts with Fe2+ ion, it become colourless. Fe2+, Fe3+ and Mn2+ ions have a pale colour. Therefore, the end point of the titration is the appearance of persistent purple colour. (One extra drop of potassium permanganate is added to the solution after the reaction is complete.)
Activated charcoal is added to the dissolved iron tablets solution. The activated charcoal can remove the red colour which comes from the outer coating of the tablets. The red colour can interrupt the appearance of the end point and so disturb the result.
Sulphuric acid is added to dissolve the iron tablets and to provide H+ ions to the reaction of Fe2+ ions and MnO4- ions. Sulphuric acid can also provide an acidic medium to Fe2+ ions. If water is add to dissolve iron tablets, the Fe2+ ions will react with OH- ions to form Fe(OH)2 (s).
1. Weight accurately of 5 iron tablets (to the nearest 0.001g) and take record of the measurement.
2. Dissolve the 5 iron tablets in about 100 cm3 of 1.0M sulphuric acid in a conical flask.
3. Stir to dissolve...