What is the purpose of adding

zinc chloride in the preparation of starch iodide paste?
Please refer to the procedure below: -
Starch Iodide Paste- Heat 100mL of water in a 250mL beaker to boiling, add a solution of 0.75g of potassium iodide in 5mL of water, then add 2g of zinc chloride dissolved in 10mL of water, and, while the solution is boiling, add, with stirring, a smooth suspension of 5g of soluble starch in 30mL of cold water. Continue to boil for 2 mins, then cool.

The purpose of adding zinc chloride in the preparation of starch iodide paste is to prevent the formation of free iodine and to increase the shelf life of the paste.

In the given procedure, zinc chloride is added after potassium iodide solution. When iodide ions (I-) from the potassium iodide react with the iodine (I2) produced during the reaction, free iodine is formed. This free iodine can make the paste unstable and cause it to deteriorate over time.

By adding zinc chloride, it forms a complex with the free iodine, converting it back into iodide ions and preventing the formation of more free iodine. This helps to stabilize the paste and prevent any discoloration or degradation over time.

To get the answer to this question, you can analyze the function of zinc chloride in the procedure and its effects on the stability of the starch iodide paste. Additionally, you can do further research on the role of zinc chloride in iodine reactions and the preservation of starch solutions.