Question

Detemine the rate of reaction between potassium Iodate (KIO3) and sodium sulphate (Na2So3) with the use of starch indicator.

Answer 1

Given Detemine the rate of reaction between potassium Iodate (KIO3) and sodium sulphite (Na2So3) with the use of starch indicator

By sulphite potassium iodate is reduced to iodide. Iodide ions are produced when sulphite ions react with potassium iodate. This reacts immediately with sulphite ions and forms iodide ions. The liberated iodine will be left free to form blue colour due to the presence of starch, and sulphite ions are completely consumed. With the increase in concentration of potassium iodate the rate of reaction increases.

Answer 2

$\textbf{determination of rate of reaction between potassium iodate}\\\textbf{and sodium sulphite with use of starch indicator}$

we know, in acidic medium, potassium iodate reduced to iodide by sodium sulphite . reactions are follows as :

$\textbf{step 1}$ : $IO_3^-+3SO_3^{2-}\rightarrow I^-+3SO_4^{2-}.....\textbf{(slow)}$
$\textbf{step 2}$ : $IO_3^-+5I^-+6H^+\rightarrow 3I_2+3H_2O......\textbf{(fast)}$
$\textbf{step 3}$ : $I_2+SO_3^{2-}+H_2O\rightarrow SO_4^{2-}+2I^-+2H^+......\textbf{(very fast)}$

in step 1 , it is clearly seen that potassium iodate is reduced to iodide ions . iodide ions, thus formed , oxidised to iodine by the reaction with more iodate ions.

in step 2, in this step, formed iodine reacts immediately with sulphite ions forming iodide ions . when sulphite ions are completely consumed , the liberated iodine won't be consumed and would give blue color, if starch is present .Thus, the above reaction can be monitored by adding a known but limited volume of sodium sulphite solution and starch solution. This is an example of clock reaction as the rate of the reaction is estimated by the time taken for the appearance of blue colour.