1. What is the color of the iodate-iodide solution being titrated with Na2S2O3 (

Question

1. What is the color of the iodate-iodide solution being titrated with Na2S2O3

(a) before the starch solution is added?

(b) after the starch solution is added?

(c) at the end point?

2. In the standardization process, when the iodate-iodide solution is acidified with H2SO4, it should be titrated immediately. Why?

3. Some cleansers contain bromate salts as the oxidizing agent. The bromate ion, BrO3 - , oxidizes the iodide to iodine as indicated in the following reaction. (a) Balance the reaction; (b) On the molar basis, which is a more effective bleaching agent, KBrO3 or NaOCl?

BrO3 - (aq) + I- (aq) ! I2(aq) + Br- (aq) (acidic)

Explanation / Answer

1)

(a) before the starch solution is added--------------> Pale yellow

(b) after the starch solution is added-------------------> Blue

(c) at the end point--------------------------------------> colorless

2) IO3- + 5I- + 6H+ ? 3I2 + 3H2O

This reaction needs presence of acid, low pH both helps air oxygen oxidize iodides to iodine and speeds up thiosulfate decomposition.

this must be used immediately otherwise I2 oxidises to Iodides again.

3) a)

Balanced equation:
BrO3{-} + 6 I{-} + 6 H{+} = 3 I2 + Br{-} + 3 H2O

b) NaOCl better bleaching agent.

it is better oxidising agent and disinfection because Cl present in this compound . it is used to prepare bleaching powder CaOCl2

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