Practical 4 - Determination of the order of a reaction Flashcards
Aim
To determine the order of reaction for the oxidation of iodide ions to hydrogen peroxide in acid solution
Apparatus
Stopwatch
100cm^3 conical flask
Stirring rod
4x 10cm3 measuring cylinder
5cm3 measuring cylinder
1cm4 measuring cylinder
Chemicals
0.1moldm3 H2O2 solution
1moldm3 H2SO4 solution
0.1moldm3 KI solution
0.005 moldm3 Na2S2O3 solution
Starch solution
Hazard with H2O2
Harmful, oxidising
Hazard with H2SO4
Irritant
How do we plan for this practical?
Decide what volumes of H2O2 solution and deionised water you will mix together to get at least 5 different concentrations of H2O2
The total volume must not exceed 5cm3
What must the total volume of H2O2 and deionised water not exceed?
5cm3
Method
- Prepare the reaction mixture by adding the following reagents into a 100 cm3 conical flask…
10.0 cm3 H,SO4 solution
10.0 cm3 Na,S20; solution
15.0 cm3 KI solution
1.0 cm3 starch solution
9.0 cm3 deionised water - Be ready with the stopwatch. Rapidly add 5.0 cm3 of H2O2 solution to the reaction mixture and simultaneously start the stopwatch. Ensure the reaction mixture is thoroughly mixed.
- Stop the watch immediately when the blue colour appears and record the time.
- Repeat steps 1-3 using the other four concentrations of H202 solution.
- Calculate the rate of reaction for each experiment.
- Plot a graph of rate of reaction against [H2O2] solution and use this to calculate the order of reaction with respect to [H202].
How to calculate initial rate
1/t
What do we do to our rate values and why?
X1000
Easier to plot the data
What kind of graph do we get as a result?
Linear
What do we need to make sure we do on the graph?
Start with the low concentrations
Order with respect to [H2O2]
1
What is rate promotional to?
[H2O2]
Rate equation for this experiment
Rate = k[H2O2]
