What happens when CuSO4 reacts with KI

The Iodometry is an analytical, titrimetric method for the quantitative determination of oxidizing substances for which no suitable indicator is available. It is to be distinguished from iodine atometry. To carry out this, the solution to be examined is mixed with an excess of iodide ions. The released iodine is then titrated with starch solution as an indicator.

Application example: Iodometric titration of copper (II)

With the help of iodometry, e.g. samples of copper (II) ions in aqueous solution can be determined very well quantitatively. This example demonstrates both the reducing (reaction 1) and the oxidizing (reaction 2) properties of iodine.

First, a sufficient excess of KI solution is added to the copper sample and then acidified to pH 1-2 with sulfuric acid. The solution is placed in a dark cabinet for 15 minutes. The following reaction takes place:

(1) 2 Cu2+ + 4 I.- → 2 CuI + I2

2 CuI (copper iodide) forms a precipitate. The resulting I2 is now with sodium thiosulphate solution (Na2S.2O3) titrated in a suitable concentration. Shortly before the end point, 1 ml starch solution is added and the titration is carried out up to the point where the color changes from blue to colorless. The equation for the titration reaction:

(2) I.2 + 2 p2O32- → 2 I.- + S4O62-

The I formed by the copper2 becomes I with thiosulfate ions- reduced. As soon as all of the iodine has been converted, the color of the starch-iodine complex changes - the end point has been reached. We know how much of the AI ​​deployed with the Cu2+ responded. Half of this value is equal to the amount of substance Cu2+.

Another important area of ​​application is the determination of the iodine value. This can be used to measure the number of double bonds in a long-chain alkene or an unsaturated fatty acid.

Category: Chemical analysis method