Rates Lab #1 - Iodine-Starch Clock                Return

Solution "A" was made by adding 4.3 g of KIO3 to 2 L of distilled water.

Moles are: 4.3 g of KIO3                = 0.02 moles
                             214.01 g/mol

Therfore molarity is 0.02 mol = 0.01 M solution
                                  2 L

Solution "B" is made by adding 4.0 g of soluble starch to 1 L of distilled water and 0.8 g of NaHSO3 in another 1 L of water. The sodium bisulphite is then acidified with 10 mL of 1 M H2SO4 and mixed.

Part 1: Effect of Concentration
You will leave the concentration of B alone but you will be diluting the concentration of A.

Mixture #
# of mL H2O
# of mL "A"
[IO3-]*
# mL of 'B'
[HSO3-]*
1
10
0
0.01 M
10
0.03 M
2
9
1
0.009 M
10
0.03 M
3
8
2
0.008 M
10
0.03 M

and so on......

Following the information in the sample data chart above, make the appropriate dilutions and react the resulting solutions. It is advised that you prepare the data table before classtime leaving only the elapsed time catagory blank. The reactions must be timed from the moment of mixing.

Record the elapsed time for the reaction of take place.

Draw a grpah of the [IO3-] vs. time

Calculate the slope of the line in three places. (high, middle & low)

Part II Effect of Temperature
Set up a personal ice bath at your lab station.

Using 10 mL of "A" and 10 mL of "B" do the following:

Mix the ingredients after you have either cooled them or warmed them.

Record the time of reaction for high, mid-range and low temperatures. The more points the better for graphing purposes.

Graph the temperature vs. time data that you have obtained.

Data Sheet for the Iodine-Clock Rate of Reaction Experiment

Effect of Concentration

    Mixture 
#
 # of mL 'A'   

 
# mL's of H2O   

 
# mL of  [IO3-]*   
mol/L
# mL of 'B'   

 
# mL of [HSO3-]*  
mol/L
Elapsed Time
        1          10               10      
        2           9               10      
        3           8               10      
        4           7               10      
        5           6               10       
        6           5               10      
        7           4               10      
        8           3                10      
        9           2               10      
* Concentration after 'A' & 'B' have been mixed but prior to reaction.

Effect of Temperature
Always use 10 mL of 'A" and 10 mL of 'B'.    Choose temperatures between 5oC and 95oC
 
        Temperature           time(sec)
     
     
     

The reactions are:

1) 2 H+ + 5 HSO3- + 2 IO3- ------> I2 + 5 HSO4- + H2O

2) H2O + HSO3- + I2 ------> 2 I- + HSO4- + 2 H+

When all the bisulphite is used up:

3) 2 I- -----> I2(s)

4) I2(s) + I-(aq) ------> I3-(aq)

5) I3-(aq) + starch -------> I3- & starch complex (blue colour)

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