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Reaction of potassium iodide with ferric chloride

Published descriptions of this reaction are quite variable và many are certainly incorrect. There is a comprehensive treatment of the reaction here which suggests that the reaction is second order with respect lớn iodide and first order with respect to ferric ions. This is consistent with the results we obtained - shown below.

Results Methods


There are no hazards associated with the reagents at the concentrations described here.

Bạn đang xem: 2 fecl3 + 2 ki → 2 fecl2 + i2 + 2 kcl

Good laboratory practices should be observed.

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Vary the concentration of potassium iodide (KI)

The results below show a typical mix of reaction curves for a reaction set containing 15mM FeCl3 & varying concentrations of KI. The reactions were performed at room temperature using the reaction mixture described in ‘Methods’.


By taking the rate of reaction from the initial slopes of the curves on the graph above the effect of concentration of KI vs rate of reaction can be plotted.


This looks lượt thích second order reaction kinetics.

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1.7 rather than 2 which may be more accurate for this complex reaction.>

Vary the concentration of ferric chloride (Iron(III)chloride, FeCl3)

The results below show the rates from a series of reaction mixtures containing 15mM KI and varying concentrations of FeCl3. The reactions were performed at room temperature using the reaction mixture described in ‘Methods’.


This looks lượt thích a first order reaction so the rate equation would be: rate = k 21 1.71>

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0.03M (30mM) solutions of KI và FeCl3 were prepared. The reaction mixture was 1cm3 of each in a 4cm3 cuvette (appropriate dilutions of whichever reactant was being varied were prepared và added as 1cm3 aliquots). The reaction is quite rapid so it is important to lớn cap, the cuvette, invert it lớn mix the contents & start taking readings as quicklyas possible. Lower concentrations would give slower reactions which might be more easy to lớn manage.