Iodine Clock Calculations
Table 1. Hypothetical times (in seconds) to color change.
a) These numbers are inserted only to serve as examples.
- 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
- 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]-
Convert your rates
- 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)
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
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.
- Calculate the H+ concentration in all solutions
Example: Solution #1
H+ = (1.753 × 10-5 M) H+ = (1.31× 10-5 M
Repeat calculations for all solutions
- Calculate the amount of I- and [IO3]- present in the solutions, not what is being consumed
(0.1 M)(0.005 L) = (x)(0.1 L) x = 0.005 M
Tablulate your results for easier viewing
- 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.
- 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).