I need guidance on tackling this assignment.

Iodine Clock Reaction – Rates of Reactions

Background: K2S2O8 (potassium persulfate) contributes the persulfate ion
and the NaI contributes the 2I- ions to the reaction being studied. The
net reaction observed is:

S2O8-2 + 2I- → 2 SO4-2 + I2

We will determine the rate law for this reaction using the following
where R is the rate of the reaction, k is the rate constant, and m and
n are the order:

R = k [S2O8-2]m [I-]n

The experiment has been designed to observe three reactions at the room
temperature to determine order and k, and a fourth experiment at an
elevated temperature to use the Arrhenius Equation to determine the
activation energy of this reaction.

When we observe the rate change in each reaction, the value of m and n
can be deduced for the ratio of R2/R1 and R3/R1 where the subscript
denotes which rate relates to it’s corresponding experiment number.

R = -Δ[S2O8-2]/Δt

We will use another reaction to determine the change in the persulfate
ion concentration, by using thiosulfate (as the reduction of the
thiosulfate ion can be easily measured). As the iodine in the reaction
is reacted with the thiosulfate, it will be completely consumed. Once
excess iodine ions are present in solution (that point where all of the
thiosulfate ions are reacted) the starch will react with the excess
iodine ions and turn the solution blue. Starch is the indicator in this
reaction that allows us to measure the time of the rate of consumption
of the thiosulfate that can then be correlated to the rate of the
persulfate reacted.

I2 + 2S2O3-2 → 2I- + S4O6-2

We can then figure out the value for the change in persulfate to use in
the rate equation above as follows:

Δ[S2O8-2] = -(1/2) Δ[S2O3-2]

Δ[S2O3-2] = Δ[S2O3-2]i - Δ[S2O3-2]f Note: (If all is consumed = 0)

ᔝ剨锠ᘀ剨锠㔀脈䩃 ⩈専脈䩡 㔀 Δ[S2O3-2]i

Therefore: Δ[S2O8-2] = -(1/2) Δ[S2O3-2]i

Experiment: Using the dilutions below, design an experiment to determine
the rate of the reaction. There are millions of examples on the
Internet.

Table of Dilutions for Each Experiment:

Ex # 0.2M NaI (ml) 0.2M NaCl (ml) 0.01M Na2S2O3 (ml) 2% Starch
0.2M K2SO4 (ml) 0.2M K2S2O8 (ml)

Ex 1 2 2 2 1 2 2

Ex 2 2 2 2 1 0 4

Ex 3 4 0 2 1 2 2

Ex 4 2 2 2 1 2 2