Order of Reaction between Iodine and Propanone

4. Plot a graph of the time at which the 10cm3 samples of the reaction mixture were added to the sodium hydrogencarbonate solution(x-axis) against the volume of sodium thiosulphate needed to react with the remaining iodine(y-axis).

Attached

5. Determine the concentration of sodium thiosulphate from the graph you plotted.

From the data of Group A ,at time=0, volume of sodium thiosulphate added should be 20.75cm3.

∵concentration of iodine in the reaction mixture
= [(1/2) (volume of sodium thiosulphate added)(molarity of sodium thiosulphate added)] /(volume of reaction mixture)
∴0.0198= [(1/2) (20.75/1000) (molarity of sodium thiosulphate added)]/(50/1000)
molarity of sodium thiosulphate added =0.095421686
                              ~0.0954M

3.   What is the order of reaction with respect to iodine?i.e. what is the value of n in the equation:
   Rate of reaction=constant[I2]n
   
   Throughout the experiment, the iodine concentration in the reaction fell as iodine was consumed by propanone In fact ,the slope of the straight line in the graph is the rate of equation. From the graph, the iodine concentration changed at a uniform rate throughout the experiment as the slope of the graph is constant. Thus, the rate of iodine concentration is independent on the iodine concentration and hence the reaction is zero order with respect to iodine. The order of reaction with respect to iodine is zero, i.e. n = 0

1. Does iodine take part in the rate determining step of the reaction between iodine and propanone?

Since the reaction is zero order with respect to iodine ,the iodine plays no part in the rate determining step of the reaction

1. Record the gradients of the graphs obtained by other four groups
   

3. Plot the gradients of graphs above against the initial volume of propanone solution added.

A graph showing the gradients of graphs above against the initial volume of propanone solution added.

3. What is the order of the reaction with respect to propanone?
   

The gradient of the graph in (9)is directly proportional to the rate of reaction and volume of propanone solution is also directly proportional to its concentration.
Since a straight line is plotted in the graph above, rate of reaction is directly proportional to the concentration of propanone. Thus, the order of the reaction with respect to propanone is 1.  

Conclusion
The order of the reaction with respect to propanone is 1 and the order of the reaction with respect to iodine is 0.

Reference

 

http://www.nelsonthornes.com/aqagce/A2%20Sample%20material/Science/Chemistry.pdf

F.6 Chemistry Notes Section V by Ms Sin W L

The End