Convert your rates to the units Mol Liter-1 Sec-1 based on how much [IO3]- was consumed (0.005 L)(0.03 M) = 1.5 × 10-4 mols of H3AsO4 Correct for Stoichiometry

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Iodine Clock Calculations

Table 1. Hypothetical times (in seconds) to color change.

Solution

Time (s)a

1

672

2

281

3

142

4

84

a) These numbers are inserted only to serve as examples.

  1. First calculate an activity coefficient from the Debye-Hückel Theory

Experiment #1 CHM364

using log  = |z × z|A where z = l, A = 0.509, I = 0.16, and  = 0.626

  1. Convert your rates to the units Mol Liter-1 Sec-1 based on how much [IO3]- was consumed

(0.005 L)(0.03 M) = 1.5 × 10-4 mols of H3AsO4

Correct for Stoichiometry

3 : 1 ratio H3AsO4 to [IO3]-

Per liter

= M

Convert your rates

Example: =

  1. Calculate the amounts of HAc (acetic acid) and Ac- (acetate) in the buffers and in all solutions (remember it is a dilution of a dilution)

Buffer A

NaAc: (0.1 L)(0.75 M) = (x)(0.5 L) x = 0.15 M

HAc: (0.1 L)(0.22 M) = (x)(0.5 L) x = 0.044 M

Solution #1

Ac-: (0.065 L)(0.15 M) = (x)(0 .1 L) x = 0.0975 M

HAc: (0.065 L)(0.044 M) = (x)(0.1 L) x = 0.0286 M

Repeat the calculations for all solutions, remember that solution 4 contains buffer B.

  1. Calculate the H+ concentration in all solutions

H+ =

Example: Solution #1

H+ = (1.753 × 10-5 M) H+ = (1.31× 10-5 M

Repeat calculations for all solutions

  1. Calculate the amount of I- and [IO3]- present in the solutions, not what is being consumed

Example

For

(0.1 M)(0.005 L) = (x)(0.1 L) x = 0.005 M

Tablulate your results for easier viewing

  1. Divide your rate law to obtain coefficients (reaction orders)

= Solve for coefficient p (you will have to use natural log)

All other components cancel out due to having the same concentration

Once, you solve for p, use your other rate laws to solve for the others.

  1. Once you have obtained all three coefficients, plug it back into the rate law to

calculate a theoretical value for k. Take an average of the four rate laws to give

you an average k, then compare to the literature value for k (k = 1.753 × 10-5 M).