Question

RATE = ([ Na2S2O3]/time) = k [I-]a [BrO3-]b [HCl]c

1A) You mix together in the proper manner the following:
10.0 mL of .0100 M Potassium Iodide
10.0 mL of .00100 M Sodium thiosulfate
10.0 mL of water
10.0 mL of .0400 M Potassium Bromate
10.0 mL of .100 M HCl
The time to turn blue is... 53 sec
1B) You also mix together in the proper manner the following:
10.0 mL of .0100 M Potassium Iodide
10.0 mL of .00100 M Sodium thiosulfate
10.0 mL of .0400 M Potassium Bromate
20.0 mL of .100 M HCl
The time to turn blue is... 14 sec
Calculate:
The Experimental value of exponent c..._______________ (a)

2) If the exponents a, b, and c have the values:
a = 1; b = 0; c = 2
CALCULATE:
Rate constant k for data in 1A...______________ (b)

Answer 1

1. As we can see in the data given , the concentration of all the reactants are kept constant in second experiment except HCl.

The concentration of HCl was made double which reduces the time approx four times to the first experiment. ( 53/14).

So the rate increaes four times that of first experiment

This indicates that rate of reaction = constant X [HCl]²

The Experimental value of exponent c = 2

b. RATE = ([ Na2S2O3]/time) = k [I-]a [BrO3-]b [HCl]c

Note:

1. 10.0 mL of .0100 M Potassium Iodide, so moles = molarity X volume = 0.01 X 10 /1000 =

or concenration = moles / total volume =   0.0001    X1000 / 50 mL =0.002 M
2. 10.0 mL of .00100 M Sodium thiosulfate; so moles = molarity X volume = 0.01 X 10 /1000 =

or concenration = moles / total volume =   0.00001  X1000 / 50 mL =0.0002M
3.10.0 mL of water
4. 10.0 mL of .0400 M Potassium Bromate ; so moles = molarity X volume = 0.04 X 10 /1000 = 0.0004

or concenration = moles / total volume =    0.0004   X1000 / 50 mL =0.008
5. 10.0 mL of .100 M HCl ; so moles = molarity X volume = 0.1 X 10 /1000 = 0.001

or concenration = moles / total volume =  0.001     X1000 / 50 mL =0.02M

RATE = ([ Na2S2O3]/time) = k [I-] [BrO3-]⁰ [HCl]² = 0.0002 / 53 = K X 0.0002 X (0.02)²

3.77 X 10^-6 = K X8X10^-8

K = 47.1 moles ^-2 X L-1 X second^-1