Chemical Kinetics: the Iodine-Clock Reaction

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EXPERIMENT 3-CHEMICAL KINETICS: THE IODINE-CLOCK REACTION

J.CHAN1 and C.CABANLIG2
1NATIONAL INSTITUTE OF MOLECULAR BIOLOGY AND BIOTECHNOLOGY, COLLEGE OF SCIENCE 2NATIONAL INSTITUTE OF MOLECULAR BIOLOGY AND BIOTECHNOLOGY, COLLEGE OF SCIENCE UNIVERSITY OF THE PHILIPPINES, DILIMAN, QUEZON CITY 1101, PHILIPPINES DATE SUBMITTED: JANUARY 8, 2013

DATE PERFORMED: DECEMBER 5, 2012

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ABSTRACT

The kinetics of the reaction between persulfate (S2O82-) and iodide (I-) ions was studied in the experiment. Temperature, concentration of reactants and catalyst presence were the different factors examined if they had an effect on the rate of reaction between S2O82- and I-. The reaction of interest was timed by measuring the interval between reactant interaction and complexation of the product I2 as signified by the sudden appearance of a blue coloration. Results of the experiment indicated that the rate is first order with respect to each reactant and that the activation energy is high implying sensitivity to temperature. It was also determined that CuSO4 is a viable catalyst for the persulfate-iodide reaction. -------------------------------------------------

INTRODUCTION

Chemical kinetics is the study of reaction rates, the study of changes in concentration of reactants or products with respect to time (Silberberg, 508). There are various factors which determine chemical kinetics and changing them allows one to effectively control the speed of a chemical reaction. Temperature, concentration of reactants and presence of a catalyst are major factors that affect reaction rates (Alcantara et al, 15). This area of study is essential because it provides information on how fast a reaction proceeds and what could be done to control its speed. Knowledge of chemical kinetics enables industries to thrive and medicines to become effective.

In this experiment, the kinetics of the reaction between persulfate (S2O82-) and iodide (I-) ions was studied. Temperature and concentration of reactants were varied to determine their influence on the reaction. The experiment also verified the catalytic effect of copper sulfate (CuSO4).

METHODOLOGY

Two sets of beakers were first prepared in the experiment. Beaker A contained KI and KCl while Beaker B contained K2SO4 and K2S2O8. The amount of chemicals placed was varied in each of the beakers for the 5 different runs as indicated in tables 1 and 2. This was done in order to determine how different reactant concentrations affect reaction rate.

Table 1. Beaker A contents per run

Run| 0.2 M KI, mL| 0.2 M KCl, mL|
1| 10| 0|
2| 5| 5|
3| 2.5| 7.5|
4| 5| 5|
5| 5| 5|

Table 2. Beaker B contents per run

Run| 0.1 M K2S2O8, mL| 0.1 M K2SO4, mL|
1| 5| 5|
2| 5| 5|
3| 5| 5|
4| 7.5| 2.5|
5| 10| 0|

5mL of 4mM Na2S2O3 was added to Beaker B in each of the 5 different runs. This is the ‘clock’ of the iodine-clock reaction and the basis for determining the reaction rate between persulfate and iodide ions. 3 drops of starch was also placed in Beaker B for all runs to serve as the indicator. The temperature of the contents was then measured to be 301.15 K.

The contents of Beaker A were then poured into Beaker B. The time between pouring and an immediate color change of the contents into blue was measured. From this data, the rate of the reaction between persulfate and iodide was measured.

A similar method was employed in determining the influence of temperature and catalyst presence on chemical kinetics. Beakers A and B contained 5 mL of each of the same chemicals. The volume of Na2S2O3 and starch placed also remained the same. 3 replicates of Beaker A and B were made. One set was heated to 323.15 K while another set was placed in an ice bath until the contents of both beakers had a temperature of 278.15 K. The contents of Beaker A were then poured into Beaker B. The third set that...
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