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# Iodine Clock

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Introduction

USING THE IODINE CLOCK METHOD TO FIND THE ORDER OF REACTION Apparatus: * Thermometer [0-110 �C] * Boiling tubes [10 cm3 �0.05] * Test tubes * Potassium iodine solution 1 mol dm-3 [15 cm3] * Potassium peroxodisulphate (VI) 0.04 mol dm-3 [10 cm3] * Sodium thiosulphate 0.01 mol dm-3 [10 cm3] * Starch solution [5 cm3] * Stopwatch [�0.5 s] Safety: Eye protection must be worn. Potassium peroxodisulphate (VI)- harmful and flammable Method: 1) First you are going to make up reaction mixture 1 from Table no 1, and measure how long it takes for the blue iodine-starch colour to appear. In each experiment use 2cm3 of sodium thiosulphate, 2cm3 of potassium peroxosulphate. Volume of each solution is 10cm3. To the first mixture add 5 cm3 of potassium iodide solution and do not add water. To second mixture add 4cm3 of potassium iodide solution and 1cm3 of distilled water. In third experiment pour 3cm3, in fourth 2cm3 and in the last one 1cm3 and add appropriate volume of water. ...read more.

Middle

Table3: The values of average time taken for the reaction to be visible and its uncertainty. Measurement Average Uncertainty 1 12.0 0 2 16.5 1.5 3 28.5 1.5 4 55.5 2.5 5 188.0 4.0 Rounded to 1 decimal place To determine the order of reaction using the iodine clock method, some of the calculation were necessary. At first, I calculated the [I-] concentration in each of 5 solutions using the equation: C[I-]= where VKI is the volume of KI solution [KI] is the KI concentration Vtotal is the total volume of solution On the example of 5th mixture: C[I-]= Table 5: The concentration of iodide in each solution Mixture Concentration of ions [mol dm-3] 1 0.5 2 0.4 3 0.3 4 0.2 5 0.1 Having calculated the concentration of [I-] ions, it is important to determine whether any reagent is in excess. To do that, I needed to calculate the concentration of iodide ions and the concentration of peroxodisulphate(VI) ions in mixture 5th. C[I-]= C[S2O3 2-]= It can be seen that the [I-] ions are in excess. ...read more.

Conclusion

The shape of the curve on the graph indicates that it is the reaction of first order. Conclusion and evaluation: The aim of the experiment was to find the order of the reaction using the iodine clock method. Using raw and calculated data I managed to determine its order and compare it with the literature. Rate of reaction and time in which it occured were necessary for the experiment. The graph showing the relationship between the iodide ions concentration and the rate of reaction was the key concept for establishing accurate order of reaction. The range of [I-] concentration was not very wide, but more than satisfying. The rate of reaction in the given range increases constantly but not directly proportional. The shape of the curve on the graph allow me to recognize the first order of reaction. Sadru Damji in "Chemistry 2nd Edition" present more accurate graph for the first order of reaction: rate [A]concentration As can be observed, the graph I created and that presented by Sadru Damji follows similar trend. My graph is not directly proportional, but its shape indicates it's a first order reaction. ...read more.

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