Question

Experiment 1084-04: lodine Clock Reaction Purpose Determine the rate law for an iodine clock reaction and study the influence of st on that reaction abruptly that it can be as startling as the sudden sound of an alarm clock, hence the clock reaction Background Information chemical equations can be written for chemical reactions, only some will proceed while others do not. Among the ones that do proceed some reactions occur as soon as reactants are mixed, while others occur over minutes, hours, or n over several years. What are the controlling in predicting if a reaction will take place and the speed at which it will? Thermodynamics can answer the question, "Will the reaction take place?" Once the reaction is capable of proceeding kinetics can answer the other question, "How fast You will study the rate of the reduction of potassium persulfate, KoS Os, with sodium iodide, Nal. The net ionic equation for the reaction is eve The rate law for this reaction is in the form of And you will need to determine the reaction orders a and b, as well as the rate constant, k. Keep in mind that exponents can not be determined by jus looking at the chemical equation the reaction will take place? The rate of a reaction is defined as the increase in molar concentration of product of a reaction per unit time or the decrease in molar concentration of reectant per unit time. The usual unit for the rate is moles per liter per sec (mol/L s or M/s). Experimentally, it has been found that a reaction rate depends on the concentrations of the reactants. Usually a higher reactant concentration increases chance of collision among the reactants per unit time causing a faster reaction rate. An equation describing the relationship between the reaction rate and the concentration of the reactants You will need a way to determine how much of the reactants were spent over the given time period. Preferably, the concentrations of the reactants should not change too much; therefore the reaction rate can be represented by the initial concentrations of reactants (the initial-rate method). In this experiment, we will couple another reaction that consumes the product, 12 very quickly. The new reaction is the reduction of is called a rate law. For the elementary reaction Note that l2, which was produced in reaction (1) is consumed as fast as it is produced by reaction (2) to regenerate two l. i.e. [门is kept constant. By keeping [S203-9 much smaller than the initial concentration of S,0, we can assure [S20,1 is also kept nearly constant when S203 is completely consumed. At this point, the 12 is no longer eliminated by the reaction and starts to accumulate. This point is signaled by sudden appearance of the dark color from the interaction of l2 with starch indicator. We can measure the time elapsed till the color appears Rate k [AIB] The proportionality constant, k, is called the ate constant in the relationship between the rate nd concentrations. The rate constant has a fixed alue as long as the reaction temperature is held nstant. The exponents, a and b, are called the action order, and are frequently, but not always, egers. More importantly, they must be termined experimentally In this experiment you will determine the rate an iodine clock reaction, and study the effects of perature and a catalyst to the reaction rate ugh there are several versions of an iodine k reaction, all of them share a common feature: completion of the reaction is signaled by the en appearance of a dark purple color. This is characteristic of the interaction between cular iodine and starch. When the reaction is ed out correctly, this color will appear so According to the reaction stoichiometries of reactions (1) and (2), two molecules of S203 are required to counteract the consumption of one molecule of S20a2. Since S2032 would have been completely consumed when the dark purple color appeared, the Δ[SO ] should be % of the initial concentration of S203 15-08-2] = ½ initial [S,03-21

answer the questions

Answer 1

e)When two colourless solutions are mixed and there is no visible reaction.But after a while a sudden olour change occurs due to the formation of starch-triIodide complex.Once thiosulphate ion has been exhausted, the colour change occurs.

f) According to the reaction stoichiometries, the reactions 1 and 2 shows that 2 molecules of S₂O_3^-2 is actually required to counteract consumption of one molecule of S₂O₈^2- . Since S₂O₃^2- has been completely consumed when dark purple colour appears.

Hence, S₂O₈^2- = 1/2 initial [ S₂O₃^-2 ]

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3) set 2. Because it contain the maximum amount of K₂S₂O₈^2-.

4) No catalyst is really required, starch is used for indication.