Tobias Curl
Candidate Number: 6063
Centre Number: 48247
Investigation into the reaction between Peroxydisultphate
ions and Iodide ions
Aims
My aims are:
1. To determine the order of the reaction with respect to (wrt) iodide ions at room
temperature using the iodine clock method.
2. To determine the order of the reaction with respect to (wrt) peroxodisulphate
ions at room temperature using the iodine clock method.
3. To determine the order of the reaction with respect to (wrt) iodide ions at room
temperature using a colorimeter.
4. To determine the order of the reaction with respect to (wrt) peroxodisulphate
ions at room temperature using a colorimeter.
5. To compare they iodine clock method with the colorimeter method.
6. To determine the rate equation for the reaction.
7. To try and create a mechanism for the reaction.
8. To determine the activation energy by changing the temperature of the
reaction.
9. To see the effect of a catalyst on the rate of the reaction.
10. To find the Ea for the catalysed reaction and compare it to the uncatalysed Ea.
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
Chemical Background (1)
The reaction between peroxodisulphate (VI) ions and iodide ions in solution forms
sulphate (VI) ions and iodine. The equation for this reaction is as follows:
S2O82- (aq) + 2I- (aq)  2SO42- (aq) + 2I2 (aq)
The two reactants, peroxodisulphate (VI) ions and iodide ions, are colourless as are
the sulphate ions. Thus the progress of the reaction can only be measured by
observing the colour of the iodine produced. The colour of the iodine will make the
solution orange/brown. The colour change can be made even more noticeable by
adding starch to the solution. When iodine forms a complex with starch it is an intense
blue/black colour.
The colour change happens gradually and would be difficult to measure the time it
takes for the iodine to be formed. A way to combat this is to add thiosulphate ions to
the solution. The thiosulphate ions turn iodine back into iodide ions and so no colour
change will happen until all the thiosulphate ions have been used up. The equation for
this reaction is:
2S2O32- (aq) + I2 (aq)  S4O62- (aq) + 2I- (aq)
The time it takes for the solution to change colour then you will know how
long it took for all the thiosulphate ions to be used up and so the same amount
of iodine produced. This will allow you to determine the initial rate of the
reaction.
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
Rate Equation 1
To calculate the rate equation for the reaction I would first have to find the amount of
I- and the amount of I2 produced.
I will use the rate calculated from method 1 to determine the rate equation.
1. Firstly I will make the general rate equation for the reaction
2. I will then need to calculate the [I-] in each of the mixtures. I will do this by
using method A below:
Method A
I will use the concentrations in method 1 and mixture 1 for this example.
Using 1.00 mol dm-3 of KI(aq)
Mixture 1 has 12 cm3 of 1.00 mol dm-3 KI
To calculate the amount of I- in the 22 cm3 mixture I will use the formula:
Amount = Concentration X Volume
So:
Amount of I- in 22 cm3 = 1.00 mol dm-3 X 12x10-3 dm3
Amount of I- in 22 cm3 = 12x10-3 mol dm3
So be able to calculate the initial rate of the reaction I will need to calculate the
amount of I- in 1000 cm3
Amount of I- in 1000 cm3 = 12x10-3 dm3 X 1000
22
3
3
Amount of I in 1000 cm = 0.545 mol dm
This method will have to be repeated for each mixture.
3. Next I will have to calculate the amount of I2 which can be produced at then
end point. I will do this by using method B below.
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
Method B
For the [I2] at the end point using 4 cm3 of 0.010 mol dm3 of S2O32- (aq) in all mixtures.
2
2
2S 2 O3  I 2  S 4 O6  2I 
2 mol
1 mol
Amount of S2O32- in 22 cm3 = Concentration X Volume
Amount of S2O32- in 22 cm3 = 0.010 mol dm3 X 4x10-3
Amount of S2O32- in 22 cm3 = 4x10-5
Amount of I2 in 22 cm3 = 4x10-5
2
Amount of I2 in 22 cm3 = 2x10-5
Amount of I2 in 22 cm3 = 2x10-5 x 1000
22
3
-4
Amount of I2 in 22 cm = 9.09x10
4. With the time and the I2 I can calculate the initial rate of the reaction for each
mixture.
5. I will then have to calculate the order of the reaction with respect to [I-] and
the [S2O82-]. I will do this by drawing 2 graphs. One of initial rate against the
[I-] and one of initial rate against [S2O82-].
6. With the order of reaction for each reactant, the concentrations and the initial
rate, I can then calculate the rate constant, k, for that temperature.
7. When I have calculated this I will have the rate constant.
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
Rate Equation 2
The rate equation gives information about how the rate depends on the concentration
for a particular reaction.
To determine the rate of the reaction it is necessary to form the rate equation for the
reaction. The rate equation for a reaction is in the form:
Rate = k [A] x [B]
Where the [A] is the concentration of A and [B] is the concentration of B.
k is the rate constant of the reaction. This constant remains the same unless the
temperature the reaction is carried out at changes. k will roughly double when the
temperature of the reaction increases by 10C.
The only way to work out the rate and the rate constant is by experiment.
Example
Reaction 2 H 2( g )  2 NO( g )  2 H 2 O( g )  N 2( g ) at 973K
Results of some studies:
[H2] /10-2 mol dm-3
2.0
2.0
2.0
1.0
4.0
[NO] /10-2 mol dm-3
2.50
1.25
5.00
1.25
2.50
The order of reaction wrt [H2]: 1
The order of reaction wrt [NO]: 2
Rate  k[ H 2 ][ NO] 2
Rate= 4.8 x10-6
[H2]= 2.0 x10-2
[NO] = 2.5 x10-2
Rate  k[H 2 ][ NO] 2
k
Rate
[ H 2 ][ NO] 2
4.8  10  6
k
(2.0  10  2 )( 2.5  10  2 )
k  9.6  10 3 mol 1 dm 3 s 1
Rate  9.6  10 3 [ H 2 ][ NO] 2
Rate /10-6 mol dm-3 s-1
4.8
1.2
19.2
0.6
9.6
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
Order of Reaction (2)
The order of reaction is the power which the reactants need to be raised to in the rate
equation.
A + B  products
Rate = k [A]m [B]n
m and n are the orders of reaction with respect to (wrt) [A] and [B]. The overall
reaction is the sum of m and n (m + n).
Example (3)
CH3 (g) + Cl2 (g)  CH3Cl (g) + Cl (g)
Rate = k [CH3] [Cl2]
The order of reaction wrt [CH3] = 1
The order of reaction wrt [Cl2] = 1
So the overall order of reaction is:
1+1=2
The order of reaction cannot be found from the chemical equation, it can only be
found from experiment.
The general rate equation for the reaction between iodide ions and peroxodisulphate
ions which is being studied would be:
2
Rate  k[S 2 O8 ] a [ I  ]b
So to find the order of reaction with respect to (wrt) [I-] ions or [S2O82-] ions I need to
workout the initial rate of the reaction and the concentration of [I-] ions and [S2O82-]
in each mixture. I will then need to plot two graphs of initial rate of I2 formed against
[I-] ions and [S2O82-]. If the graph gives a straight line then the order of reaction wrt
[ion] would be 1st order. If the graph is curved then the order of reaction wrt [ion]
would be 2nd order. If no accurate line of best fit can be drawn then the initial rate
doesn’t depend of the [ion] so the order is zero. Examples can be seen the graphs
below:
1st Order
2nd Order
Zero Order
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
Reaction Mechanisms (4)
With the rate equation for a reaction formed it can now be linked to the reaction
mechanism. A reaction mechanism usually involves several steps. The rate
determining step, the slowest step is given in the rate equation.
Example
Reaction between 2-bromo-2-methylpropane and hydroxide ions (diagram 1).
CH3
CH3
CH3
C
Br
+
CH3
OH-
C
OH
+
Br-
CH3
CH3
(Diagram 1 Reaction between 2-bromo-2-methylpropane and hydroxide ions)(4)
Rate  k[(CH 3 ) 3 CBr ]
Order 1 wrt [(CH3)3CBr]
Order 0 wrt [OH-]
[OH-] is not in the rate equation because it does not take part in the slow rate
determining step.
The reaction takes place in 2 steps.
Firstly the C-Br bond breaks heterolytically (diagram 2):
CH3
CH3
CH3
C
Br
CH3
CH3
C+
+
Br-
CH3
(Diagram 2 bond breaks heterolytically)(4)
This step is the slow rate determining step and does not contain OH- so hence the rate
does not depend on the [OH-].
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
The next step is the fast step which does involve the OH-:
CH3
CH3
C+
CH3
+
CH3
OH-
CH3
C
OH
CH3
(Diagram 3 fast step)(4)
This reaction happens in 2 steps but some reactions can happen in less or more steps.
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
Activation Energy (Ea)
A reaction has an activation energy value, the energy it needs to start the reaction.
This Ea value can be found by relating the rate constant, k, with the temperature, T, of
the reaction. The two are related by the Arrhenius equation.
Arrhenius
constant
Rate
Constant
k  A e
The base
for natural
logs
Activation
Energy

Ea
RT
Temperature
constant
(R) Molar
gas constant
To find the Ea firstly we need to take the natural logs of all the items in the Arrhenius
equation:
k  A e

Ea
RT
ln k  ln A  ln( e
ln k  ln A 

Ea
Rt
)
Ea
RT
Since the rate constant:
Put
1
into the equation in place of k:
Time
1
Ea
 ln A 
Time
RT
1
Ea
ln

 ln A
Time
RT
1
Ea 1
ln

  ln A
Time
R T
( y  mx  c)
ln
k  Rate
ConcentrationChange
1
Rate 

Time
Time
1
k
Time
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
So the graph which would be plotted would be ln
ln
1
1
Vs
Time T
1
Time
1
T
The Ea can then be found from the gradient of the graph or:
gradient 
 Ea
2.303R
or
 Ea  gradient  2.303R
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
Collision Theory (5)
The main idea behind the Collision Theory is that “reactions occur if the particles of
reactants collide, provided they collide with a certain minimum kinetic energy.”
Example:
Two particles, one of ozone the other of chlorine moving in the stratosphere. If they
collide with enough energy they will react. The amount of energy needed for the two
to react is called the activation enthalpy for the reaction. A way to speed up the
reaction would be to increase the concentration of the particles. This will obviously
increase the chance of a successful collision. This can be seen in the diagram 4 below.
Higher Concentration
Low Concentration
Ozone
Chlorine
(Diagram 4: collision theory) (6)
One more way to increase the rate of a reaction is to bring the particles closer together
this would involve increasing the pressure. However this method of increasing the
rate can only be achieved with gases.
Another way to increase the rate of a reaction is to increase the temperature. This
gives the particles more energy so there will be more successful collisions.
We can work out how much more they collide because the average speed is
proportional to the absolute temperature.
Example (7)
Increase the temperature from 300 K to 310 K then the average speed increases by a
factor of (310/300)1/2 is about 1.016 which is an increase of 1.6%. However the rate
usually increases by 200%-300%.
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
The distribution curves below in diagram 5 for 300 K and 310 K with energy greater
than 50kJ mol-1 shows what happens to the rate.
(Diagram 5: Enthalpy Profiles) (8)
As can be seen in the graph a higher proportion of molecules have enough energy to
react.
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
Catalysts
A catalyst is a substance which speeds up/increases the rate of the reaction. The
catalyst is not used up or changed by the reaction.
A catalyst is usually a transition metal in a powder or as an oxide so that it has a
larger surface area.
The catalyst works by providing a surface for the reactants to gather on and so react.
This leads to more collisions and more successful collisions as the catalyst lowers the
activation enthalpy of the reaction. This can be seen in diagram 6 below:
(Diagram 6: Example of a heterogeneous catalyst) (9)
There are 2 different types of catalysts: Homogenous and Heterogeneous.
Homogeneous catalysts are in the same state as the reactants, eg, liquid reactants,
liquid catalyst. Heterogeneous catalysts are in a different state to the reactants, eg,
liquid reactants, solid catalyst. An example of a heterogeneous catalyst used in
industry is Iron in the Habber process.
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
A catalyst works by providing an alternate reaction pathway which has a lower
activation enthalpy. This means that more molecules will have the right energy to
react. This can be shown in an enthalpy profile (diagram 7) as below:
(Diagram 7: Enthalpy Profiles for catalysed and uncatalysed reactions) (10)
As can be seen on the catalysed reaction there is a dip in the middle. This is where an
intermediate compound is formed with the catalyst before going on the make the final
product.
Transition metals are very good catalysts. This is because of the availability of the 3d
and 4s electrons in the metals.
Catalysts can also be poisoned. A catalyst poison stops a catalyst from functioning
properly. In heterogeneous catalysts a poison molecule will be more strongly
absorbed than the reactant molecules and so the catalyst becomes inactive.
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
Methods
Making a Standard Solution (11)
To make a standard solution these steps must be followed:
1. Accurately weigh 5g of sodium thiosulphate in a beaker and record the exact
mass.
2. Add about 25 cm3 of sulphuric acid and stir until all the solid has dissolved.
3. Transfer the solution into a 250 cm3 volumetric flask using a funnel pouring it
down the stirring rod so that none of the solution goes down the side of the
beaker.
4. Rinse the beaker into the flask with sulphuric acid to ensure that all the sodium
thiosulphate is transferred to the flask.
5. Add sulphuric acid to the flask until it is about 1 cm3 below the 250 cm3 mark
and make it up to 250 cm3 by adding the sulphuric acid with a dropping
pipette.
6. Put the stopper in the flask and invert a few times to ensure that the solution is
homogenous.
Making a Starch Solution (12)
These steps must be followed to make a starch solution.
1. Measure out 2.5g of soluble starch in to a beaker.
2. Add about little cold distilled water and stir until a thin creamy suspension is
formed.
3. Transfer the solution into a 250 cm3 volumetric flask using a funnel pouring it
down the stirring rod so that none of the solution goes down the side of the
beaker.
4. Rinse the beaker into the flask with distilled water to ensure that all the starch
is transferred to the flask.
5. Boil the distilled water and add to the suspension stirring so that no lumps are
formed.
6. Add distilled water to the flask until it is about 1 cm3 below the 250 cm3 mark
and make it up to 250 cm3 by adding the distilled water with a dropping
pipette.
7. Put the stopper in the flask and invert a few times to ensure that the solution is
homogenous.
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
Method 1
This method deals with aim 1: “To determine the order of the reaction with respect to
(wrt) iodide ions at room temperature using the iodine clock method.” and aim 2: “To
determine the order of the reaction with respect to (wrt) peroxodisulphate ions at
room temperature using the iodine clock method.” The method is sometimes called
the iodine clock method.
Equipment
4 Burettes
Beaker
Boiling Tubes
Syringe
Stopwatch
Thermometer
Chemicals
Potassium Iodide
Sodium Thiosulphate
Distilled Water
Starch Solution
Potassium Peroxodisulphate
 1.00 mol dm-3
 0.0100 mol dm-3
 0.0400 mol dm-3
1. Firstly I will set up the 4 burettes. I will wash them with distilled water and
then the solution which they will contain I will also label them.
2. I will fill each of the burettes with potassium iodide solution, sodium
thiosulphate solution, starch solution or distilled water.
3. I will then fill a boiling tube with mixture 1 from the table below but not the
potassium peroxodisulphate as this will start the reaction:
Mixture Volume of
potassium
iodide/cm3
1
12
2
10
3
8
4
6
5
4
6
2
Volume of
sodium
thiosulphate/cm3
4
4
4
4
4
4
Volume
of
water/cm3
0
2
4
6
8
10
Volume of Volume of potassium
starch/cm3 peroxodisulphate/cm3
2
2
2
2
2
2
4
4
4
4
4
4
4. I will shake the mixture.
5. I will measure the temperature of the mixture with a thermometer.
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
6. I will then add the potassium peroxodisulphate with a syringe and start the
stopwatch as soon as the first drop is added.
7. As soon as the mixture turns blue/black I will stop the stopwatch and note
down the time.
8. I will repeat the experiment until I have 2 results which are concordant within
5% of each other.
9. I will then repeat the steps above for each of the reaction mixtures.
These volumes will allow me to find the order of reaction with respect to [I-] ions. To
find the order with respect to [S2O82-] ions I will need to vary the volume of the
[S2O82-] ions instead of the [I-] ions. I will repeat the steps above and use the volumes
below.
Mixture Volume of
potassium
iodide/cm3
1
4
2
4
3
4
4
4
5
4
6
4
Volume of
sodium
thiosulphate/cm3
4
4
4
4
4
4
Volume
of
water/cm3
0
2
4
6
8
10
Volume of Volume of potassium
starch/cm3 peroxodisulphate/cm3
2
2
2
2
2
2
12
10
8
6
4
2
Results Table
I will use a results table like this to record my results:
Mixture
Time 1
Time 2
Time 3
Time 4
Time 5
1
2
3
4
5
6
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
Method 2
This method deals with aim 3: “To determine the order of the reaction with respect to
(wrt) iodide ions at room temperature using a colorimeter.” and aim 4: “To determine
the order of the reaction with respect to (wrt) peroxodisulphate ions at room
temperature using a colorimeter.” These methods do not require the addition of
sodium thiosulphate or starch as the absorbance can be measured to a certain point
and so can be a gradual colour change.
Equipment
2 Burettes
Beaker
Boiling Tubes
Syringe
Stopwatch
Thermometer
Colorimeter
Chemicals
Potassium Iodide
Distilled Water
Potassium Peroxodisulphate
 1.00 mol dm-3
 0.0400 mol dm-3
1. Firstly I will set up the 2 burettes. I will wash them with distilled water and
then the solution which they will contain I will also label them.
2. I will fill each of the burettes with either potassium iodide solution or distilled
water.
These first 2 steps are the same as method 1. The next steps are slightly different.
3. I will setup the colorimeter with the blue filter.
4. I will then fill a test tube with mixture 1 from the table below but not the
potassium peroxodisulphate as this will start the reaction:
Mixture Volume of
potassium
iodide/cm3
1
1.2
2
1.0
3
0.8
4
0.6
5
0.4
6
0.2
Volume
of
water/cm3
0.0
0.2
0.4
0.6
0.8
1.0
Volume of potassium
peroxodisulphate/cm3
0.4
0.4
0.4
0.4
0.4
0.4
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
I have divide the volumes from method 1 by 10 and so will need to multiply the rate
found at the end by 10 so the iodine clock experiment and the colorimeter experiment
can be compared.
5. I will shake the mixture so that is it evenly mixed.
6. I will measure the temperature of the mixture with a thermometer.
7. I will then transfer the mixture to a cuvette with a dropping pipette.
8. I will then add the potassium peroxodisulphate with a syringe and start the
stopwatch as soon as the first drop is added.
9. When the absorbance of the mixture reaches 1 then I will stop the stop watch.
10. I will repeat the experiment until I have 2 results which are concordant within
5% of each other.
11. I will then repeat the steps above for each of the reaction mixtures.
For aim 4 I will use these mixtures and use the method above:
Mixture Volume of
potassium
iodide/cm3
1
0.4
2
0.4
3
0.4
4
0.4
5
0.4
6
0.4
Volume
of
water/cm3
0.0
0.2
0.4
0.6
0.8
1.0
Volume of potassium
peroxodisulphate/cm3
1.2
1.0
0.8
0.6
0.4
0.2
Results Table
I will use a results table like this to record my results:
Mixture
Time 1
Time 2
Time 3
Time 4
Time 5
1
2
3
4
5
6
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
Method 3
This method deals with aim 8: “To determine the activation energy by changing the
temperature of the reaction.”
This method will be nearly the same as method 1. I will carry out the same procedures
except I will heat up the solution and the potassium peroxodisulphate separately
before adding the potassium peroxodisulphate to start the reaction.
Equipment
4 Burettes
Beaker
Boiling Tubes
Syringe
Stopwatch
Thermometer
Chemicals
Potassium Iodide
Sodium Thiosulphate
Distilled Water
Starch Solution
Potassium Peroxodisulphate
 1.00 mol dm-3
 0.0100 mol dm-3
 0.0400 mol dm-3
1. Firstly I will set up the 4 burettes. I will wash them with distilled water and
then the solution which they will contain I will also label them.
2. I will fill each of the burettes with either potassium iodide solution, sodium
thiosulphate solution, starch solution or distilled water.
3. I will then fill a boiling tube with mixture 4 from the table below but not the
potassium peroxodisulphate as this will start the reaction:
Mixture Volume of
potassium
iodide/cm3
4
4
Volume of
sodium
thiosulphate/cm3
4
Volume
Volume of Volume of potassium
of
starch/cm3 peroxodisulphate/cm3
3
water/cm
8
2
4
4. I will shake the mixture so that is it evenly mixed.
5. I will heat up the mixture and the potassium peroxodisulphate with a water
bath.
6. I will measure the temperature of the mixture with a thermometer.
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
7. I will then add the potassium peroxodisulphate with a syringe and start the
stopwatch as soon as the first drop is added.
8. As soon as the mixture turns blue/black I will stop the stopwatch and note
down the time.
9. I will repeat the experiment until I have 2 results which are concordant within
5% of each other.
10. I will then repeat the steps above for different temperatures.
11. I will then use the Arrhenius equation to calculate the activation energy.
k  A e

Ea
RT
I will record my results in a table like this:
Temperature - °C
Temperature - K
30
35
40
45
50
55
303
308
313
318
323
328
I will then plot a graph of ln
Time - t/s
1
1
against .
Time
T
Example:
ln
1
Time
1
T
ln (1/t)
1 1
K
T
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
Method 4
This method deals with aim 9: “To see the effect of a catalyst on the rate of the
reaction.”
This method will use the procedures from method 1 and I will add a transition metal
catalyst to the reaction mixture.
Equipment
4 Burettes
Beaker
Boiling Tubes
Syringe
Stopwatch
Thermometer
Chemicals
Potassium Iodide
Sodium Thiosulphate
Distilled Water
Starch Solution
Potassium Peroxodisulphate
 1.00 mol dm-3
 0.0100 mol dm-3
 0.0400 mol dm-3
I will try out the catalyst (21 + 22):



Iron (III) Chloride
Chromium (II) Sulphate
Manganese (II) Sulphate
I will add the catalyst in a 1.00 mol dm-3 solution.
I will the carry out the Iodine Clock Experiment as in method 1 and see which gives
me the fastest time. I will then carry out the experiment using jus that catalyst over the
6 mixtures:
wrt iodide ions
Mixture Volume of
potassium
iodide/cm3
1
12
2
10
3
8
4
6
5
4
6
2
Volume of
sodium
thiosulphate/cm3
4
4
4
4
4
4
Volume
of
water/cm3
0
2
4
6
8
10
Volume of Volume of potassium
starch/cm3 peroxodisulphate/cm3
2
2
2
2
2
2
4
4
4
4
4
4
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
and wrt to the peroxodisulphate ions
Mixture Volume of
potassium
iodide/cm3
1
4
2
4
3
4
4
4
5
4
6
4
Volume of
sodium
thiosulphate/cm3
4
4
4
4
4
4
Volume
of
water/cm3
0
2
4
6
8
10
Volume of Volume of potassium
starch/cm3 peroxodisulphate/cm3
2
2
2
2
2
2
12
10
8
6
4
2
This will allow me to see if the rate is affected by a catalyst.
Results Table
I will use a results table like this to record my results:
Mixture
Time 1
Time 2
Time 3
Time 4
Time 5
1
2
3
4
5
6
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
Method 5
This method deals with aim 10: “To find the Ea for the catalysed reaction and
compare it to the uncatalysed Ea.” To meet this aim I will have to carry out method 3
but using the catalyst which I found to be most effective in method 4.
Equipment
4 Burettes
Beaker
Boiling Tubes
Syringe
Stopwatch
Thermometer
Chemicals
Potassium Iodide
Sodium Thiosulphate
Distilled Water
Starch Solution
Potassium Peroxodisulphate
Catalyst
 1.00 mol dm-3
 0.0100 mol dm-3
 0.0400 mol dm-3
 1.00 mol dm-3
I will use this mixture:
Mixture Volume of
potassium
iodide/cm3
4
4
Volume of
sodium
thiosulphate/cm3
4
Volume
Volume of Volume of potassium
of
starch/cm3 peroxodisulphate/cm3
water/cm3
8
2
4
And I will record the results in a table like this with these temperatures:
Temperature - °C
Temperature - K
30
35
40
45
50
55
303
308
313
318
323
328
Time - t/s
Long10 (1/t)
1 1
K
T
1
1
against
.
Time
Time
The gradient of this will allow me to find the Ea for the catalysed reaction and hence
compare the catalysed with the unanalysed reaction.
I will then plot a graph of log 10
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
Justifications
1. I will use burettes instead of a measuring cylinder because a burette is
designed for very accurate measurements. Burettes have low precisions errors
so are very good for the accurate measurements which I need to do. The
precision error for a burette is: I will wash each burette with distilled water
first so that any chemicals already on the burette will be washed away. I will
also wash them with the solution they will hold because if I just put the
solution I was going to use in it would be diluted by the water that has just
cleaned the burette and so the concentration would not be correct. This would
affect my results. I will label them so I know which chemical is which as they
are all colourless.
2. I will fill the burettes with the chemicals so that I can use one burette for all
repeats and mixtures.
3. I am going to use a boiling tube because it can hold the volume of mixture I
need to use.
4. I need to shake or swirl the mixture so that it is mixed properly. If I did not
mix the solutions properly the reaction could be affected.
5. The temperature needs to be measured because the rate of a reaction differs
with temperature. The rate constant for a reaction is only valid for a certain
temperature. If the temperature varies then the rate constant will not be valid
and so any calculations done using the rate constant at a different temperature
will be incorrect.
6. I need to add the potassium peroxodisulphate as fast as possible because the
reaction will start as soon as the first drop is added. This is the reason why a
burette cannot be used to add the potassium peroxodisulphate as it is too slow.
7. I need to use the blue filter on the colorimeter because blue is the
complimentary colour for orange which the mixture will change colour to. I
used the colour wheel (diagram 8) to find this:
Red
Violet
Orange
Yellow
Yellow/Green
Blue/Violet
Blue
(diagram 9: colour wheel) (13)
Blue/Green
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
8. I have to use lower volumes because the colorimeter cannot hold more than a
few cm3 of solution.
9. I will use an electric water bath instead of a Bunsen burner as it will allow me
to accurately change the temperature to what I want.
10. I will need to heat the mixture and the potassium peroxodisulphate separately
because otherwise the temperature could change when the potassium
peroxodisulphate is added.
11. I will perform the reaction in the water bath to maintain the constant
temperature.
12. I will use 6 mixtures for each method because this will give 6 points on the
graphs. Even if there are a couple of anomalous results the trend could still be
determined. If however I only used 3 mixtures, 2 anomalous results would ruin
the trend.
13. I choose to repeat my readings because by repeating them any errors can be
shown up and it makes the over all result reliable.
14. I have chosen to use the volumes I have because using the larger volumes
makes errors smaller so the end results will be more accurate. I am using the
concentrations because these will give me the results I need without being too
dangerous.
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
Risk Assessments (14)
Potassium Iodide (15)
Chemical
Potassium Iodide – KI
Concentration – 1.00 mol dm-3
General Hazards


Irritant
 Irritating to eyes and skin
Harmful  May cause sensitization by skin contact
 May cause sensitization by inhalation
Special Handling Information


Eye protection (safety goggles) must be worn at all times.
Wear gloves
First Aid
What to do if Potassium Iodide:




Gets in you eye – the eye should be rinsed with water for 10 minutes and seek
medical attention.
Gets in your mouth or is swallowed – Give plenty of water and seek medical
attention. Do not induce vomiting.
Gets on your skin – Wash off skin with plenty of water.
Gets on you cloths – All contaminated clothing must be removed.
Procedures

Is split on the floor or bench – Cover with a mineral absorbent and scoop up as
much as possible. Rinse area of spill with a mop or cloth thoroughly.
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
Sodium Thiosulphate (16)
Chemical
Sodium Thiosulphate – Na2S2O3
Concentration – 0.0100 Mol dm-3
General Hazards

Irritant
 Irritating to eyes, skin and repository system
Special Handling Information

Eye protection (safety goggles) must be worn at all times.
First Aid
What to do if Sodium Thiosulphate:




Gets in you eye – the eye should be rinsed with water for 10 minutes and seek
medical attention.
Gets in your mouth or is swallowed – Give plenty of water and seek medical
attention.
Gets on your skin – Wash off skin with plenty of water.
Gets on you cloths – All contaminated clothing must be removed.
Procedures

Is split on the floor or bench – Cover with a mineral absorbent and scoop up as
much as possible. Rinse area of spill with a mop or cloth thoroughly.
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
Potassium Peroxodisulphate (17)
Chemical
Potassium Peroxodisulphate – K2S2O8
Concentration – 0.0400 Mol dm-3
General Hazards

Harmful  May cause sensitization by skin contact
 May cause sensitization by inhalation
 If swallowed
Special Handling Information


Eye protection (safety goggles) must be worn at all times.
Wear gloves
First Aid
What to do if Potassium Peroxodisulphate:




Gets in you eye – the eye should be rinsed with water for 10 minutes and seek
medical attention.
Gets in your mouth or is swallowed – Give plenty of water and seek medical
attention. Do not induce vomiting.
Gets on your skin – Wash off skin with plenty of water.
Gets on you cloths – All contaminated clothing must be removed.
Procedures

Is split on the floor or bench – Cover with a mineral absorbent and scoop up as
much as possible. Rinse area of spill with a mop or cloth thoroughly.
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
Iron (III) Chloride (18)
Chemical
Iron (III) Chloride – FeCl3
Concentration – 1.00 Mol dm-3
General Hazards

Irritant
 With skin contact
 With eye contact
Special Handling Information


Eye protection (safety goggles) must be worn at all times.
Wear gloves
First Aid
What to do if Iron (III) Chloride:




Gets in you eye – the eye should be rinsed with water for 10 minutes and seek
medical attention.
Gets in your mouth or is swallowed – Wash out mouth with a couple of glasses of
water and seek medical attention.
Gets on your skin – Wash off skin with plenty of water.
Gets on you cloths – All contaminated clothing must be removed.
Procedures

Is split on the floor or bench – Cover with a mineral absorbent and scoop up as
much as possible. Rinse area of spill with a mop or cloth thoroughly.
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
Chromium (II) Sulphate (19)
Chemical
Chromium (II) Sulphate – CrSO4
Concentration – 1.00 Mol dm-3
General Hazards

Irritant

Harmful
 With skin contact
 With eye contact
 By ingestion
Special Handling Information


Eye protection (safety goggles) must be worn at all times.
Wear gloves
First Aid
What to do if Chromium (II) Sulphate:




Gets in you eye – the eye should be rinsed with water for 10 minutes and seek
medical attention.
Gets in your mouth or is swallowed – Wash out mouth with a couple of glasses of
water and seek medical attention.
Gets on your skin – Wash off skin with plenty of water.
Gets on you cloths – All contaminated clothing must be removed.
Procedures

Is split on the floor or bench – Cover with a mineral absorbent and scoop up as
much as possible. Rinse area of spill with a mop or cloth thoroughly.
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
Manganese (II) Sulphate (20)
Chemical
Manganese (II) Sulphate – MnSO4
Concentration – 1.00 Mol dm-3
General Hazards

Harmful
 By inhalation
 With skin contact
Special Handling Information


Eye protection (safety goggles) must be worn at all times.
Wear gloves
First Aid
What to do if Manganese (II) Salt:




Gets in you eye – the eye should be rinsed with water for 10 minutes and seek
medical attention.
Gets in your mouth or is swallowed – Wash out mouth with a couple of glasses of
water and seek medical attention.
Gets on your skin – Wash off skin with plenty of water.
Gets on you cloths – All contaminated clothing must be removed.
Procedures

Is split on the floor or bench – Cover with a mineral absorbent and scoop up as
much as possible. Rinse area of spill with a mop or cloth thoroughly.
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
References
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
(11)
(12)
(13)
(14)
(15)
(16)
(17)
(18)
(19)
(20)
(21)
(22)
Activity EP6.4 Salters A-Level Chemistry Activity Sheets. Page 191
Chemical Ideas by Salters Advanced Chemistry. Published by Heinemann in 2000.
ISBN 0-435-63120-9. Pages 230 and question 1d on page 238
Chemical Ideas by Salters Advanced Chemistry. Published by Heinemann in 2000.
ISBN 0-435-63120-9. Question 1d on page 238
Chemical Ideas by Salters Advanced Chemistry. Published by Heinemann in 2000.
ISBN 0-435-63120-9. Page 235 (first diagram, step 1 and step 2)
Chemical Ideas by Salters Advanced Chemistry. Published by Heinemann in 2000.
ISBN 0-435-63120-9. Page 221
Chemical Ideas by Salters Advanced Chemistry. Published by Heinemann in 2000.
ISBN 0-435-63120-9. Page 221 – figure 1
Chemical Ideas by Salters Advanced Chemistry. Published by Heinemann in 2000.
ISBN 0-435-63120-9. Pages 223-224 (last paragraph on page 223)
Chemical Ideas by Salters Advanced Chemistry. Published by Heinemann in 2000.
ISBN 0-435-63120-9. Pages225 - figure 6
Chemical Ideas by Salters Advanced Chemistry. Published by Heinemann in 2000.
ISBN 0-435-63120-9. Page 240 - figure 18
Chemical Ideas by Salters Advanced Chemistry. Published by Heinemann in 2000.
ISBN 0-435-63120-9. Page 242 - figure 19
Activity El 2.1 Salters A-Level Chemistry Activity Sheets.
Nelsonthornes.comhttp://www.nelsonthornes.com/downloads/sec_science/0748771549/1/1_3_1_5_b.htm
Chemical Ideas by Salters Advanced Chemistry. Published by Heinemann in 2000.
ISBN 0-435-63120-9. Page 155 - figure 54
Oxford University Chemical Safety Database Searcherhttp://ptcl.chem.ox.ac.uk/MSDS/msds-searcher.html
http://ptcl.chem.ox.ac.uk/MSDS/PO/potassium_iodide.html
Hazcards – No. 95 Sodium Salts
http://ptcl.chem.ox.ac.uk/MSDS/PO/potassium_persulfate.html
Hazcards – No. 55 Iron Salts
Hazcards – No. 24 Chromium Salts
Hazcards – No. 60 Manganese Salts
AQA GCEA and AS Chemistry Further Exemplar Assessment Material for Practical
Work Feb 1999. Page 22
Advanced Level Practical Work in chemistry. A teachers Guide 1991. John Parkinson.
Blackwell Education. Pages 19 and 20.
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
AS and A2 work
Reference Number
1
2
3
4
5
6
7
8
9
10
11
13
Studied at As or A2
A2
A2
A2
A2
AS
AS
AS and A2
AS
AS
AS
AS
A2
Unit
EP
EP
EP
EP
A
A
A and EP
A
DF and A
DF and A
EL
SS
Tobias Curl
Candidate Number: 6063
Centre Number: 48247
Requisition List
Chemicals
Chemical
Potassium Iodide
Sodium Thiosulphate
Starch Solution
Potassium Peroxodisulphate
Distilled Water
Iron (III) Chloride Solution
Chromium (II) Sulphate Solution
Manganese (II) Sulphate Solution
Concentration
 1.00 mol dm-3
 0.0100 mol dm-3





0.0400 mol dm-3
N/A
1.00 mol dm-3
1.00 mol dm-3
1.00 mol dm-3
Equipment
4 Burettes 0 cm3 – 50 cm3
2 Beakers 250 cm3
1 Beaker 500 cm3
6 Boiling Tubes
Syringe
Stopwatch
2 Thermometers: 0°C – 100°C and 0°C – 50°C
Colorimeter
Cuvettes
Water bath
Volume
1000 cm3
500 cm3
500 cm3
500 cm3
N/A
500 cm3
500 cm3
500 cm3