Iodine Clock Reaction

In reference to the collision theory, molecules act as small spheres that collide and bounce off each other, transferring energy among themselves when the collide. In order for a reaction to occur, there must be collisions between molecules. Through experimentation, factors are discovered that influence the reaction rates of chemical reactions include the concentration of reactants, temperature, surface area, the physical state of reactants, and a catalyst. This experiment regarding the factors that affect reaction rate tests the effects of increased concentration and

“The iodine clock reaction was discovered by the Swiss chemist Hans Heinrich Landolt in 1886.” (Scilearn, 2017). There are many variations of the iodine clock reaction but they all involve two colourless solutions being mixed and after a specific period of time, the mixed solutions turn dark blue. The iodate variation of the clock reaction involves the reaction between iodate ions. These being, IO3-, hydrogen sulfite ions, HSO3-, and hydronium ions, H+. To ensure the blue colour change, starch is needed to be added to the solution, reacting with I2. The delay in colour change occurs because as soon as I2 is formed, it immediately reacts with any HSO3- still present and is converted into colourless I-. After all the HSO3- has been consumed, the concentration of the I2 increases and begins reacting with the starch. This is why the dark blue colour is suddenly present. The reaction of the starch reacting to turn the solution a deep blue colour. The reaction occurs in two steps. The first step generates iodide ion (I in Equation 2, which occurs slowly and is the rate determining step. “A rate determining reaction is the slowest step in a reaction mechanism and is assumed to be equal to the overall reaction rate because the reaction cannot go faster than the slowest step.”(Webcache.googleusercontent.com, 2017 ).

Introduction: First discovered by Hans Heinrich Landolt in the 19th century, the Iodine Clock reaction is what is described as a chemical clock reaction, and today is one of only few known to science. It is useful as a tool in determining the rate of a chemical reaction due to a marked change in the color of the reacting solution when a particular reaction has been completed. The process is also practical as an introduction to reaction rates and kinetics. A solution of hydrogen peroxide is mixed with one containing potassium iodide, starch and sodium thiosulfate. After a varying amount of time the colorless mixture suddenly turns dark blue which is one of a number of reactions related to the iodine clock.

Many factors effect reaction rates, two shown above include temperature and concentration. Concentration affects the rate of reactions because the more concentrated a solution the more likely collisions between particles will be. This is simply because there are more particles present to collide with each other. When the temperature is higher, particles will

Abstract: This two part experiment is designed to determine the rate law of the following reaction, 2I-(aq) + H2O2(aq) + 2H+I2(aq) + 2H2O(L), and to then determine if a change in temperature has an effect on that rate of this reaction. It was found that the reaction rate=k[I-]^1[H2O2+]^1, and the experimental activation energy is 60.62 KJ/mol.

To investigate the effects of changing the concentration of the reactants and catalysts in the peroxydisulfate/iodide clock reaction. The six investigations differ by either changing the concentration of reactants (potassium peroxydisulfate and potassium iodide), changing the concentration of catalyst, changing the catalyst used, and by changing the temperature of the solutions. The clock reaction method was used as a way of measuring the rate of reaction so I could see how the varying concentrations and temperatures affected the rate of reaction.

By heating to refluxing, the temperature and thermal energy were controlled during the experiment. Heating the reaction is important because it is required in order for the bonds to break to cause a chemical reaction. Breaking bonds also means requiring energy and that is where activation energy comes into play. All chemical reactions has to overcome an energy barrier to generate the product from the reactant.

Reactions are defined as having three states, reactants, transition state, and products. The transition state is the highest energy state of the system, essentially acting as the activation energy. If the molecules collide with more kinetic energy than the transition state energy, then the reaction will transpire, and products will be produced.4 The experimentally determined activation energy for the bleaching reaction between green dye #3 and bleach was 12328 J/mol, as compared to the activation energy of 7580 J/mol for the reaction between green dye and cetylpyridinum chloride, the experimental was larger.3 This means it takes far more energy to cause the bleach to react with green dye #3 than it does for green dye to react with cetylpyridinum chloride. Moreover, the reactions are not the same, so the activation energies will be dissimilar, nonetheless, both reactions cause the decolorization of green dye.

Procedure A was an experiment on observing how different effects of extreme temperatures have on enzyme catalysis. There are three parts in this experiment. In part 1, we took a syringe labeled “H2O2” and used it

activation energy in a reaction, allowing the chemical reaction to take place at a faster rate. A

Activation energy is the minimum amount of energy for a reaction to undergo. Only a small amount of collisions between

In the Iodine Clock reaction experiment, we stall a reaction by having Iodine changed rapidly by two chemicals between it’s two forms. These two forms have slightly different properties. The first form of iodine is I⁻. This is not an indicator of starch. The second form of iodine is I₂. This type is an indicator of starch(a chemical that changes color in the presence of a starch).

Then, a fixed amount of sodium bisulfite/sulfuric acid/starch solution was added to each iodate solution, and the time needed to turn the mixed solution blue was recorded. Based on the measured time, reaction rate was calculated. It was found that the higher the concentration of iodate ions, the faster the reaction time. It was also found that the order of reaction was approximately 1. The result matched my prediction.

In the results we can see that the purple pink solution of potassium permanganate (MnO4-) was reduced to a colourless solution of manganese ions (Mn2+).

| Measure the time taken for the potassium permanganate solution to decolourise from purple to colourless by using stopwatch