You tried to find the rate law for the reaction of below. Table of below shoes t

Question

You tried to find the rate law for the reaction of below. Table of below shoes the compositions of test tubes used to study the kinetics of this reaction S_2O_8^2- + 2I^- (aq) rightarrow 2 SO_4^2_ (aq) + I_2 (aq) What is the reason to have KCl and K_2SO_4 in the reaction? Iodine clock reaction was used to measure the rate for this reaction. Reactions involved in the Iodine clock were shown below. I_2(aq) + 2 S_2O_3^2- (aq) rightarrow 2I^+ (aq) + S_4O_6^2- (aq) I_2(aq) + starch (aq) rightarrow blue iodine starch complex What are the roles of the thiosulfate ion in the reaction? What is the change of concentration with respect to [S_2O_8]^2- in the above reaction?

Explanation / Answer

the reaction above is iodine clock reaction.

2S2O32 + I2 S4O62 + 2I

(a) The rate coefficient (k) of ionic reactions depends on the ionic strength or salinity of the solution. Potassium chloride (KCl) and potassium sulfate (K2SO4) are used to maintain the ionic strength of the solutions.

(b) Sodium thiosulfate is used to reduce iodine back to iodide before the iodine can complex with the starch to form the characteristic blue-black color.

(c) As the reaction proceeds, the concentration of reactants reduces due to its consumption to oxidize iodide ion to iodine. Hence the change in the concentration with respect to persulphate is denoted by (-ve) sign.

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