Research Question Find the rate expression for a reaction between propanone and iodine

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Research Question

Find the rate expression for a reaction between propanone and iodine

Background Information

The rate of reaction can be defined as the “increase in molar concentration of a product of a reaction per unit time” or the “decrease is molar concentration of a reactant per unit time.” A quantitative way of showing this is through the rate expression. We can find this by performing a series of experiments: changing the concentration of one of the reactants whilst keeping the others constant.

For example:

A + B ↔ C

The reaction above would have the rate expression

R (rate of reaction) = k [A] x [B] y


  • The rate of reaction is measured in mol dm-3 s-1
  • [A] [B] is the product of the concentrations of the reactants measured in mol dm-3
  • x and y are the powers which the concentrations are raised to,
    as well as the order of reactants A and B. They usually have values between 0 and 2
  • k is the rate constant, with varying unites dependant upon the order of the reaction
  • the over all order of the reaction is x + y

The equation giving the reactions we will consider is:

                                   Dilute H2SO4

CH3COCH3 (aq) + I2 (aq)               CH3COH2I(aq)  + HI(aq)

(Dilute sulfuric acid is used as a catalyst as the reaction is quite slow)



The greater the concentration of the reactant the greater the rate of reaction. By increasing the concentration of the catalyst, rate of reaction should also increase due to the resulting lower activation energy.




  • 1M solution of Propanone
  • 1M solution of H2SO4
  • 0.0038M solution of Iodine
  • 0.0076M solution of Iodine
  • 0.0114M solution of Iodine
  • Distilled water        


  • Conical flask
  • 3 measuring cylinders (50ml, 25ml and 10ml)
  • White tile
  • Stopwatch

Safety Precautions

  • Wear safety goggles to protect eyes, as the highly flammable propanone can cause irritation
  • Make sure the laboratory is ventilated to avoid inhalation of toxic gases i.e. iodine. It can cause severe damage to the upper respiratory tract.
  • Wear a lab coat to avoid skin contact with chemicals
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In each experiment, the independent variable is the concentration of the substance which is being changed. The dependant variable is the rate of reaction, shown by the time taken for the solution to become colourless. Controlled variables are the total volume of the solution, temperature and the concentration of the other two substances.

Experiment 1: Changing the concentration of Iodine

  • Measure out 35ml of propanone in the 50ml measuring cylinder and 10ml of sulfuric acid in the 25ml measuring cylinder. Measure out 5ml of the 0.0142M solution of ...

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