Chemistry Iodine Clock

First Order Reaction

In a first order reaction if the concentration of a reactant is doubled the rate of the reaction will double, e.g. if reactants A and reactant B react in 30 seconds, if concentration of reactant A is doubled the rate of reaction will also double so the time taken will drop by half. This is what you would expect from every reaction but isn’t always the case.

Second Order Reaction

In a second order reaction if the concentration of a reactant is doubled the rate of the reaction will quadruple, e.g. if reactants A and reactant B react in 30 seconds, if concentration of reactant A is doubled the rate of reaction will go up by 4 times, so the time taken will drop by a quarter.

Rate Equation

                

Rate = k [reactant A]m [reactant B]n

Where:

• [A] and [B] are the initial concentrations of reactants A and B
• k is the rate constant
• m is the order of reaction with respect to reactant A
• n is the order of reaction with respect to reactant B
• (n + m) is the overall order of the reaction (3)

To find out the order of reaction of substrate A, experiments need to be conducted where the concentration of substrate A need to stay the same. By keeping the concentration the same of substrate A and getting enough results to plot a graph we can see what order of reaction it is.

For the zero order reaction the graphs should look something like this:-

Rate of Reaction against Concentration of Reactant

Concentration against Time

The graphs for the first order should look something like this:

Rate of reaction against Concentration

Concentration against time

The graphs for the second order reaction should look like this:

Rate of reaction against concentration

Concentration against time

Plan

Making a standard solution

A standard solution is a solution of known concentration which is mostly measured in mol dm-3

Standard solution of Sodium thiosulphate

We need to calculate how many moles we need. This can be worked out by this equation:

Number of moles         =         concentration         x         volume

We will be using 0.010 mol dm-3 of Sodium thiosulphate (Na2S2O3) and making 250cm3 of solution. The 250cm3 needs to be converted in decimetres cubed (dm3) so we need to divide 250cm3 by 1000 to get 0.25dm3

Number of moles         =  0.010  x  0.25

                        = 0.0025 moles

Now that we have worked out the number of moles we can work out the mass of Sodium thiosulphate needed by the following equation:

Mass (measured in grams) =        Mr (molecular mass)        x        Moles

We need to work out the molecular mass of Sodium thiosulphate Na2S2O3

Element                                Mr

Sodium (Na)                        22.989  x  2        =  45.978

Sulphur (S)                                32.065  x  2        =  64.130

Oxygen (O)                                15.999  x  3        =  47.997

                                Total Mr                =  158.105

We have the molecular mass now we can work out the mass needed.

Mass         = 158.105  x  0.0025

        = 0.3953g

Instruction to make standard solution of Sodium thiosulphate

1. Take lab safety to consideration i.e. wear lab coat, goggles and gloves if needed

2.  Measure the solid on an accurate balance, Tare the balance so it shows zero (use a balance that measures to at least 2 decimal places to make it more accurate)

3. Put the solid in a clean beaker (clean beaker with distilled water just to be sure)

4. Dissolve the solid with distilled water; use a clean glass rod to stir if necessary.

5. Once dissolved transfer the solution to a 250cm3 volumetric flask

6. Rinse the beaker out with distilled water (and glass rod if used); do this at least twice so less chance of any solution left in beaker (or on glass rod)

7. Add more distilled water to the volumetric flask if needed to get the level just under the mark.

8. Using a pipette add drop by drop on distilled water into the flask until the bottom of the meniscus is on the line. Make sure your eyes are in level with the line to ensure you don’t add more distilled water than needed.

9. Insert the lid on the top and shake the solution to homogenise it. This ensures that the solution is mixed properly.

10. Write on the flask the name of solution, that way you won’t get mixed up when you make other solutions.

Standard solution of Potassium Iodide

We need to calculate how many moles we need. This can be worked out by this equation:

Number of moles = concentration  x  volume

We will be using 1.00 mol dm-3 of Potassium Iodide and making 250cm3 of solution. The 250cm3 needs to be converted in decimetres cubed (dm3) so we need to divide 250cm3 by 1000 to get 0.25dm3

Number of moles         = 1.00 x 0.25

                        = 0.25 moles

Now that we have worked out the number of moles we can work out the mass of Potassium Iodide needed by the following equation:

Mass (measured in grams) =        Mr (molecular mass)        x        Moles

We need to work out the molecular mass of Potassium Iodide (KI)

Element                                Mr

Potassium (K)                        39.098

Iodine (I)                                126.904

                Total Mr        =  166.002

We have the molecular mass now we can work out the mass needed.

Mass         = 166.002  x  0.25

        = 41.501g

To make the solution follow instructions on page 8

Standard solution of Potassium Peroxodisulphate (VI) (K2S2O8)

We need to calculate how many moles we need. This can be worked out by this equation:

Number of moles = concentration  x  volume

We will be using 0.040 mol dm-3 of Potassium Peroxodisulphate (K2S2O8) and making 250cm3 of solution. The 250cm3 needs to be converted in decimetres cubed (dm3) so we need to divide 250cm3 by 1000 to get 0.25dm3

Number of moles         = 0.040 x 0.25

                        = 0.01 moles

Now that we have worked out the number of moles we can work out the mass of Potassium Peroxodisulphate (K2S2O8) needed by the following equation:

Mass (measured in grams) =        Mr (molecular mass)        x        Moles

We need to work out the molecular mass of Potassium Peroxodisulphate (K2S2O8)

Element                                Mr

Potassium (K)                        39.098 x 2 = 78.196

Sulphur(S)                                32.065 x 2 = 64.130

Oxygen (O)                                15.999 x 8 = 127.992

                Total Mr        =  270.318

We have the molecular mass now we can work out the mass needed.

Mass         = 270.318 x 0.25

        = 67.580g

To make the solution follow instructions on page 8

Once all the standard solutions were made I set the apparatus listed below as shown in Diagram 1

Equipment needed for experiment:

Burettes x4

Pipettes x1

Funnels x4

Test tubes x5

Boiling tubes x5

Test tube holder

Clamps x4

Beakers x4

Stop clock

Starch (freshly made)

Potassium Peroxodisulphate solution

Potassium Iodide solution

Sodium Thiosulphate solution

Distilled water

Diagram 1:

This experiment is to see how fast the starch changes colour. These are the amounts of each solution I will be using.

In this experiment the independent variable will be Potassium Iodide, the amount of distilled water will vary to keep the overall volume the same; the amount of Sodium thiosulphate, Starch and Potassium Peroxodisulphate will be controlled.

Method to do Preliminary experiment

1. Put safety equipment on i.e. lab coat, goggle and gloves

2. Set the clamp and the burette as shown:

3. Rinse a burette with Potassium Iodide (KI), do this at least 3 times to make sure that the burette has no other solution in it.

4. Repeat step 3 with the other solutions.

5. Take a test tube and accurately measure and add the amount shown of Potassium Peroxodisulphate in mixture 1

6. Take a boiling tube and put all solutions of quantity from mixture 1 apart from Potassium Peroxodisulphate

7. Pour the Potassium Peroxodisulphate into the test tube and immediately start the stop clock.

8. Record the time taken for the starch to change colour into a table. (see table below)

9. Repeat steps 5 to 8 so you get at least 3 separate results.

10. Repeat steps 5 to 9 but with quantities from different mixtures

Method to do Experiment- Change of concentration of Potassium Peroxodisulphate  

1. Put safety equipment on i.e. lab coat, goggle and gloves

2. Set the clamp and the burette.

3. Rinse a burette with Potassium Iodide (KI), do this at least 3 times to ensure that the burette has no other solution in it.

4. Repeat step 3 with the other solutions.

5. Take a test tube and accurately measure and add the amount shown of Potassium Peroxodisulphate in mixture 1

6. Take a boiling tube and put all solutions of quantity from mixture 1 apart from Potassium Peroxodisulphate

7. Pour the Potassium Peroxodisulphate into the test tube and immediately start the stop clock.

8. Record the time taken for the starch to change colour into a table. (see table below)

9. Repeat steps 5 to 8 so you get at least 3 separate results.

10. Repeat steps 5 to 9 but with quantities from different mixtures

Experiment-Change in Temperature

In this experiment the independent variable will be the temperature. The solutions will be controlled. In my experiment I chose mixture 3.

Apparatus:

Thermometer x3

Burettes x4

Pipette x1

Funnels x4

Test tubes x5

Boiling tubes x5

Test tube holder

Clamps x4

Beakers x4

Stop clock

Starch (freshly made)

Potassium Peroxodisulphate solution

Potassium Iodide solution

Sodium Thiosulphate solution

Distilled water

Water bath (which can vary the temperature)

Method

1. Put safety equipment on i.e. lab coat, goggle and gloves

2. Set the clamp and the burette.

3. Rinse a burettes with the solutions, do this at least 3 times to make sure that the burette has no other solution in it.

4. Take a test tube and accurately measure and add the amount shown of Potassium Peroxodisulphate in mixture 3

5. Take a boiling tube and put all solutions of quantity from mixture 3 apart from Potassium Peroxodisulphate

6. Set the water bath temperature to 30oC

7. Using the thermometer ensure that the temperature is at 30oC

8. Put the boiling tube and the test tube from steps 4 and 5 into the water bath

9. Take two thermometers and put one into the boiling tube and the other into the test tube so see if the temperature is 30oC.

10.  Add the K2S2O8 into the boiling and immediately start the stop clock

11. When reaction is finished record the result into a table.

12. Repeat the experiment with same temperature so you have at least 3 results.

13.  Repeat steps 4 to 12 but with different temperatures e.g. 40oC, 50oC (see table below)

Increasing the temperature will increase the chances of successful collisions between reactants. This is because the molecules have more kinetic energy so can collide with more power making the chance of collision to be higher.

The rate of temperature change can be calculated by using the Arrhenius equation. The equation is shown below. The symbols are explained in the diagram.

Values for the symbols

R has the value of 8.314 x 10-3 kJ mol-1K-1

e has the value of 2.71828 (natural log)

T has the value of oC + 273.15 (measured in Kelvin)

Experiment- Using Transition metal solutions

This experiment will show if the transition metal solutions affect the rate of reaction.

For this experiment I have chosen Mixture 3:

The transition metal solutions used (1cm3 of 0.1mol):

Copper Sulphate

Nickel Sulphate

Ferrous Sulphate

Zinc sulphate

Apparatus needed:

Transition metal solutions

Burettes x4

Pipette x1

Funnels x4

Test tubes x3for each transition metal solution

Boiling tubes x3 for each transition metal solution

Test tube holder

Clamps x4

Beakers x4

Stop clock

Starch (freshly made)

Potassium Peroxodisulphate solution

Potassium Iodide solution

Sodium Thiosulphate solution

Distilled water

Method

1. Put safety equipment on i.e. lab coat, goggle and gloves

2. Set the clamp and the burette as shown in diagram 1

3. Rinse the burettes with the solutions, do this at least 3 times to ensure that the burette has no other solution in it.

4. Take a test tube and accurately measure and add the amount shown of Potassium Peroxodisulphate in mixture 3

5. Take a boiling tube and put all solutions of quantity from mixture 3 apart from Potassium Peroxodisulphate

6. Use a measuring cylinder and measure out 1cm3 of the transition metal solution

7. Add the solution to the boiling tube from step 5

8.  Add the K2S2O8 into the boiling and immediately start the stop clock

9. When reaction is finished record the result into a table.

10. Repeat the experiment with same transition metal solution so you have at least 3 results. (see table below)

11.  Repeat steps 4 to 10 but with different transition metal solutions.

Analysis of Preliminary Experiment 1

In the preliminary experiment I followed the table below.

The results I received from doing this experiment are:

Analysis of Experiment 2- changing the temperature

From getting the results from the 1st experiment I decided to choose Mixture 3 as the mixture. Talk about temp increase etc why u chose mixture 3

The results are as follows:

Experiment- Using Transition Metal solutions

The results I recorded for the transition metal ion solutions are:

1cm3 of 0.1mol of each transition metal was used

Experiment- Using Transition Metal Solids

References

Tuesday 1st April 2008   3:11pm

ENGINEERING PROTEIN                 RATES OF CHEMICAL REACTIONS

Wednesday 2nd April 2008

3. Revise A2 Chemistry Salters OCR ISBN 0-435-58347-6

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Visited Monday 7th April 2008