Analysis of an [OA]

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Flashcards on Analysis of an [OA], created by I Shouldn't be awake on 02/06/2018.
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Flashcards by I Shouldn't be awake, updated more than 1 year ago
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Question Answer
What titration to use Iodine/thiosulfate
What can it be used to determine? ClO- in bleach Cu2+ in copper(ii) compounds Cu content in copper alloys
Step 1. Add a std. sol of Na2S2O3 to the burette
Step 2. Prepare solution of OA to be analysed and pipette into a conical flask
Step 3. Add an excess of KI. OA will react with I- to produce I2. Solution turns yellow-brown
Step 4. Titrate this solution with the Na2S2O3 Iodine will be reduced back to I- and brown colour fades gradually, making end point difficult to see.
Step 5. When end point is being approached, the iodine colour has faded enough to become a pale straw colour
Step 5. As end point is being approached and iodine colour has become pale straw, add small amount starch indicator. Deep blue-black colour forms
Step 6 As more Na2S2O3 is added the blue-black colour fades, at end point all iodine will have reacted and blue-black colour disappears.
Why starch at end? As iodine-starch complex very stable at high iodine conc., would require more titrant
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