Question

Using the reaction mixture in Problem 1, a student found that it took 230 seconds for the color of the I2 to disappear.

Answer 1

The reaction mixture of problem 1 includes 10mL of 4.0 M acetone = 10 mL 1.0 M HCl = 10 mL 0.0050 M I2 = 20 mL H2O. if this is true then the procedure is the following:

In order to find the total volume of reaction then you need to do like this: 
V = 10 mL + 10 mL + 10 mL + 20 mL = 50 mL 
[I2]o = (0.005 mol I2 / 1 L I2 solution) (10 mL I2 solution) / 50 mL = 0.001 M 
To first order, the reaction rate is 0.001 M / 230 s = 4,3 e-6 M/s 
Then if you want to find the rate yoe need to use the following formula:
 k [CO(CH3)2]^a [I2]^b [HCl]^c 
So: 4,3 e-6 = k (4 M * 10 mL / 50 mL)^a (1e-3 M)^b (1 M * 10 mL / 50 mL)^c