To Observe the Effect of Temperature on the Rate of the Iodine Clock Reaction Using Ammonium Persulfate

Aim: To observe the effect of temperature on the rate of the iodine clock reaction using ammonium persulfate

Assessment criteria: Design

Variables:

Table 1.1: List of dependent and independent variables. S.No | Dependent variables | Independent variables | Controlled variables | 1. | Rate of reaction | Temperature | Concentration | 2. | - | - | Pressure | 3. | - | - | Volume |

Hypothesis:

The iodine clock reaction is an experiment that demonstrates chemical kinetics in action. The iodine clock reaction exists in several variations; this particular experiment is conducted according to the Persulfate variation.

Two colorless solutions are to be mixed; though there is no visible reaction initially. Shortly thereafter, the liquid suddenly turns to a shade of dark blue. This clock reaction uses ammonium persulfate to oxidize iodide ions to iodine.

2I- (aq) + S2O82- (aq) → I2 (aq) + 2SO42- (aq) Subsequently, sodium thiosulfate is used to reduce iodine back to iodide before the iodine can complex with the starch to form the characteristic blue-black color.

I2 (aq) + 2S2O32- (aq) → 2I- (aq) + S4O62- (aq)

An important factor that affects the rate of reaction is temperature. Temperature is proportional to the average kinetic energy, which is the energy associated with motion. All reactions have energy equivalent to the activation energy of the reaction. When we increase the temperature of a reaction, the average kinetic energy of the reactants increase. This change results in two things.

Firstly, there is an increase in the amount of collisions. Secondly, more molecules now have an energy equal to the activation energy and can now form products. More collisions, more energy, and a greater probability of favorable collisions leads to an increase in reaction rate. Again, the opposite is true if we decrease the temperature.

Apparatus required:

55 ml of Ammonium Persulfate (0.1 M), 55 ml of Sodium Thiosulfate (0.02 M), 55 ml of Potassium Iodide (0.3 M), 55 ml of Distilled Water, 8 beakers, 4 Burettes, Starch solution, stirrer, clock or a stop watch

Procedure:

1. 50 ml of each chemical must be taken in distinctively labeled beakers.

2. Four burettes, each labeled with the chemical it contains, must be set up.

i. Ammonium Persulfate or (NH4)2S2O8 ii. Sodium Thiosulfate or Na2S2O3 iii. Distilled Water or H2O iv. Potassium Iodide or KI

3. The Burettes must be rinsed several times with water.

4. The Burettes must be rinsed twice with the appropriate chemical (approximately 2 or 3 ml) and the rinsing waste must be disposed.
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5. The appropriate amounts of the first three chemicals must be meticulously added to the 50 ml beaker as given in the table below.

Table 1.2: Amount of chemicals to add in the beakers. Amount of Mixture (in ml) | S.no | (NH4)2S2O8 | Na2S2O3 | H2O | KI | Total volume | 1. | 12.0 | 1.0 | 0.0 | 12.0 | 25.0 | 2. | 9.0 | 1.0 | 3.0 | 12.0 | 25.0 | 3. | 6.0 | 1.0 | 6.0 | 12.0 | 25.0 | 4. | 3.0 | 1.0 | 9.0 | 12.0 | 25.0 | 5. | 12.0 | 1.0 | 3.0 | 9.0 | 25.0 | 6. | 12.0 | 1.0 | 6.0 | 6.0 | 25.0 |

6. 4 or 5 drops of starch solution must be added.

7. The appropriate amount of Potassium Iodide must be measured into a separate beaker.

8. Potassium Iodide must be swiftly mixed into the 50 ml beaker.

9. The clock must be started while the mixture is constantly stirred.

10. The clock must be carefully stopped as soon as the mixture turns blue in color.

11. The time must be recorded on a data sheet.

12. The procedure must be repeated for other mixtures at different temperatures. The observations must be recorded tables such as table 1.2.

Temperature/T/°C | 5 | 10 | 15 | 20 | 25 | Time for reaction/t/s | | | | | |

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[ 1 ]. Wikipedia contributors. "Iodine clock reaction." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 30 Jun. 2013. Web. 25 Jul. 2013.
[ 2 ]. “The Iodine clock reaction”. http://msmcgregor.weebly.com/uploads/6/7/3/8/6738691/ch12labreport.pdf