Remaining Time: 12 minutes, 32 seconds. Question Completion Status: Question 1 I
ID: 876589 • Letter: R
Question
Remaining Time: 12 minutes, 32 seconds. Question Completion Status: Question 1 In the reaction of H202 and IF, a quantitative amount of S2032 is added ; starch solution is also added. The balanced equation for the reaction is H202(aq) + 31-(aq) + 2H+ l3. (aq) + H2O (l) a. What is the purpose of S203? b What is the purpose of the starch solution? c. Why is it necessary that the S2032 be measured quantitatively, but not the starch ? d. What changes would be observed if the starch were omitted from the reactions ? T TT Arial 3(12pt) T. ·-·-··Explanation / Answer
a. We need a method to accurately measure the rate of reaction between iodide ion and peroxide. The sulphate ions help us to determine the exact rate of reaction. They react with the iodine formed due to oxidation of iodide ion by peroxide.
S2O3-2 + I2 --> 2I- + S4O6-2
b. Starch is used as indicator here, which forms a complex with iodine ( amylose of starch adsorb Iodine) to form a blue balck complex.
c. Starch is an indicator so no need to add it quantitatively however the the addition of thiosulfate ions (S2O32