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 as follows:
Zinc chloride serves as a catalyst in this reaction. It helps to enhance and facilitate the formation of the desired starch-iodine complex, which gives the characteristic blue-black color that is used to test for the presence of starch.
By adding zinc chloride to the mixture, it helps to speed up the reaction between the iodine and the starch, thereby increasing the intensity of the blue-black color produced. This allows for an easier visual detection of the presence of starch in the solution.
Overall, the addition of zinc chloride in the preparation of starch iodide paste helps to improve the sensitivity and accuracy of the starch test by promoting the formation of a more pronounced color change when starch is present.
The purpose of adding zinc chloride in the preparation of starch iodide paste is to act as a catalyst for the reaction between potassium iodide and starch.
In the procedure you provided, a solution of 0.75g of potassium iodide in 5mL of water is added to 100mL of boiling water. This forms a solution of iodine ions (I-) in water.
Next, 2g of zinc chloride dissolved in 10mL of water is added. Zinc chloride dissociates in water to produce zinc cations (Zn2+) and chloride ions (Cl-). The presence of zinc cations acts as a catalyst for the reaction between iodine ions and starch.
Finally, a smooth suspension of 5g of soluble starch in 30mL of cold water is added to the boiling solution while stirring. The starch molecules have a tendency to form helical structures, and the addition of the iodine ions leads to the formation of a blue-black color complex, known as starch-iodine complex.
Zinc chloride helps in the formation of this complex by providing the necessary conditions for the reaction between iodine ions and starch. The zinc ions interact with the iodine ions, facilitating their reaction with the starch and resulting in the formation of the blue-black complex.
In summary, zinc chloride acts as a catalyst in the reaction between potassium iodide and starch to form the starch-iodine complex, which gives the paste its characteristic blue-black color.