Stoichiometric Titration Of Copper (II) Su

In this experiment iodometric titration is done using an unknown concentration of copper(II) sulfate in a 100ml volumetric flask (A43). The solution had a light blue colouration after it was topped up to the graduation mark, which is expected of a copper(II) solution.

From the stoichiometric calculations it is possible to deduce that the number of moles of thiosulfate ion is the same the number of moles of copper(II) ion by looking at reaction 1&2.

Before commencement of the experiment the apparatus used were conditioned with D.I. water to remove any existing particles or compounds that could have affected the titration results. After which, the solution of copper(II) sulfate diluted with D.I. water was prepared in a conical flask for one titration.

Concentrated acid is added into the conical flask as an acidic buffer to provide better results for reaction 1. Also in a more acidic solution it can enable all thiocyanate ions to react with iodides salts as seen in reaction 3. However, if there is a presence of excess iodide ions in an acidic solution, it can form iodine which will increase the amount of Na2S2O3 needed to titrate the solution for it to reach its end point, providing inaccurate results.

On performing the first titration, after the weighing boat of KI was added the colour of the solution changed to a brownish yellow colour and was then immediately titrated with Na2S2O3. Na2S2O3 dissociate to thiocyanate ion and sodium ion. This thiocyanate ion is then used as seen in reaction 2 to reduce iodine into iodide, through this reaction it gets oxidised to tetrathionate ion. The concentration of free iodine in the solution is directly related to the intense dark blue colour of the solution. As the concentration drops the colour of the solution begins to become paler as lesser free iodine is being

Despite the titration being performed thrice to attain the average titrant which would help improve accuracy, several errors happened contributing to inaccuracies. Some of these are misjudging the colour at endpoint and inaccurate reading of the volume in the burette due to parallax error or presence of air bubbles, which resulted in the amount of titrant recorded to be inaccurate. Also by using the same pipette for different solutions without rinsing it with D.I. water in between and when addition of solid reagents, not all the reagent may have been added both contributing to error leading to slight inaccuracies. To further increase accuracy, solutions that were involved in the reaction with iodine should be