ZnCl2 serves as a preservative. See
http://books.google.com/books?id=NFGSSSbaWjwC&pg=PA500&lpg=PA500&dq=zinc+chloride+starch+iodide+paste&source=bl&ots=V64YQciurs&sig=pwvOtYdmsSjIvK2ezPwOcsHaVWU&hl=en&ei=zbV2TdT_IqeC0QHIyd3nBg&sa=X&oi=book_result&ct=result&resnum=6&ved=0CDkQ6AEwBQ#v=onepage&q=zinc%20chloride%20starch%20iodide%20paste&f=false
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.
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