Rates of Chemical Reactions

Rates of Chemical Reactions

Purpose of the Experiment:

In this laboratory exercise the Rate Constant k for the oxidation of Iodate (IO-) by bisulfite (H2SO3) will be measured.

IO3- (aq) + 3 H2SO3  I- (aq) + 3 SO42- (aq) + 6 H+ (aq) (Eq. 1)

This reaction is referred to as a clock reaction because the progress of (Eq. 1) is monitored by a secondary clocking reaction which consumes the product HSO3- as it is produced and triggers a color change when the clocking reagent is itself completely consumed.

As long as any bisulfite ion is present, none of the Iodate produced in (Eq. 1) remains; it is consumed as quickly as it is produced. As soon as the bisulfate is used up (Eq. 2), Iodate will begin to appear in the solution. The presence of iodate is then dramatically detected by the formation of a blue aqueous starch (Eq. 3) then the reaction is said to “Clock” at this point.

IO3- (aq) + 6 H+ (aq) + 5 I- (aq) 3 I2 (aq) + 3 H20 (l) (Eq. 2)

I2 (aq) = Starch (aq)  starch-I2 (aq, dark) (Eq. 3)

Summary of the Procedure:

First gather a well plate and three plastic micropipets. The well plate will allow multiple experiments and the each of the three pipets will belong to its own solution to prevent cross contamination. Take one plastic micropipet and stretch half the pipet and then cut it at a 45° angle along the thinnest part to insure that the drops are all the same size, this pipet will the use for the H2SO3 solution. Gather the other two pipets and draw a line of 5cm from the tip, this will allow you to add the same amount each time. The 5cm line will be an equivalent volume of 10 drops of solution. Using the concentration chart below add the following to 5 wells of the well plate. Please note that the bisulfate