Topic: Iodometry

1. the reason why the Cu2+ solution has to be titrated immediately after addition of KI

Answered above.

To understand why the Cu2+ solution has to be titrated immediately after the addition of KI in iodometry, it is important to know the principle of iodometry and the reaction involved.

Iodometry is a titration method used to determine the concentration of oxidizing agents, primarily those that can oxidize iodide ions (I-) to iodine (I2). In this case, the Cu2+ solution is acting as an oxidizing agent.

When KI (potassium iodide) is added to a Cu2+ solution, a redox reaction occurs. The Cu2+ ions in the solution act as an oxidizing agent and oxidize the iodide ion (I-) to iodine (I2) while being reduced to Cu+ ions. The reaction is as follows:

2Cu2+ + 4I- -> 2Cu+ + I2 + 4Cl-

The iodine (I2) that is formed in this reaction is the substance that can be titrated to determine the concentration of the Cu2+ solution.

Now, the reason why the titration should be done immediately after the addition of KI is because iodine (I2) can easily escape into the atmosphere, resulting in a loss of iodine and therefore an inaccurate measurement.

Iodine has a relatively high vapor pressure, which means it can readily vaporize from its solid or liquid state into the gas phase. This property makes iodine volatile and prone to evaporation. Hence, if the solution is kept standing for a long time, iodine molecules may escape into the air, leading to a loss in concentration.

To ensure accurate results, it is crucial to titrate the Cu2+ solution immediately after adding KI, before any significant evaporation of iodine can occur. By performing the titration promptly, we can minimize the loss of iodine, ensuring accurate determination of the concentration of the Cu2+ solution.