# How Do You Find the Concentration of I- in the Iodine Clock Reaction?

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In summary, the conversation revolves around determining the concentration of I- involved in the Iodine Clock Reaction. The equation m1v1=m2v2 is mentioned, but the speaker is unsure of its application. They conducted nine reactions using different solutions and observed a dark blue/black color change after a minute. The speaker then asks for help in finding the concentration of I- in the reaction and is advised to use the equation C1V1=C2V2. They also discuss the rate of the reaction and how to calculate it using the change in concentration over time. The speaker is unsure if they need to consider the coefficients in the reaction.
TrueStar

## Homework Statement

Find the concentration of I- involved in the Iodine Clock Reaction

## Homework Equations

I think this will involve m1v1=m2v2 --- but I am not sure.

## The Attempt at a Solution

We did nine 'iodine clock' reactions to demonstrate chemical kinetics. I'll use the second one as an example.

We added 7.50mL of 0.200 M KI, 2.50ml of 0,200 KCl, and 5.00mL of 0.0050 S2O32-, and one drop of starch to one flask. We then added 5.00mL of S2O82- to another flask.

We then mixed them together in a beaker. The total amount of solution is 20mL. It turns dark blue/black in about a minute.

I need to figure out the concentration of I-. I understand that the reaction I need to investigate is:

2I-(aq)+S2O82-(aq) $$\rightarrow$$I2+2SO42-

I'm not sure how I can get the concentration from this. I know how to get the concentration of KI, but I don't know how to get only the I-.

Again, I think it has to do with the equation listed above, but I'm not sure.

I've read up more on this and think I have my answer.

KI is ionic, so in a solution the salt will turn into K+ and I-.

Since KI is one to one, if 0.200 M of KI, that means I have 0.200 M of I-. Is this correct?

You have 0.200M I- in the solution that you mixed with others - which is (from the pov of I-) just a dilution.

And yes, dilution can be calculated with C1V1 = C2V2. See http://www.chembuddy.com/?left=concentration&right=dilution-mixing. You will just need final volume, which can be easily calculated assuming volumes are additive. In general they are not, but differences are negligible in this case.

Yes, that makes sense. Yesterday made for a nice refresher course in dilutions and ionic solutions.

I have another question concerning the Iodine Clock; I don't think the lab instructor was entirely clear on getting the rate from the timing agent.

He said that in order to find the rate for I-, use the following equation

$$\Delta$$[S2O32-] / $$\Delta$$t

I understand that our initial concentration for thiosulfate is always the same at 1.25x10-3 and that the final concentration will always be zero since it's used up.

However, don't the coefficients need to be considered? The equation in question is:

I2(aq)+2S2O32-(aq)$$\rightarrow$$2I-+S4O62-(aq)

That tells me that the rate for thiosulfate should be multiplied by -1/2 and the iodine should be multiplied by -1.

For example, my first iodine clock reaction took 50 seconds for the starch-iodine complex to appear. I started with 1.25x10-3 concentration of thiosulfate. Using the rate equation, I end up -1.25x10-3 and divide that by 50 since that's how many seconds the reaction took. That gives me an answer of -2.5x10-5, but then I must multiply this by -1/2 because the coefficient of the thiosulfate in the chemical reaction is 2. This gives me 1.25x10-5. I then multiply this by 50 (since this equals the change of concentration of iodine divided by the change in time which is 50 seconds) and that will give me the rate for iodine.

Am I on the right track? I want to be sure, because I have eight other reactions to calculate and graph.

I would first like to commend you on your thorough explanation of the experiment and your understanding of the chemical reaction involved. The equation you have identified is correct and you are on the right track in using the equation m1v1=m2v2 to find the concentration of I-.

To solve for the concentration of I-, we need to use the data provided in the experiment. From the given data, we know that the total volume of the solution is 20mL. We also know the initial concentration of KI to be 0.200 M and the volume of KI used to be 7.50mL.

Using the equation m1v1=m2v2, we can calculate the moles of I- present in the solution as follows:

(0.200 M)(7.50mL) = (x moles)(20mL)

x= 0.075 moles of I-

Since we know the total moles of I- present in the solution, we can now calculate the concentration of I- by dividing the moles by the total volume of the solution:

Concentration of I- = 0.075 moles/ 20mL = 0.00375 M

Therefore, the concentration of I- involved in the iodine clock reaction is 0.00375 M.

I hope this helps in your understanding of the experiment and the calculation involved. Keep up the good work in your scientific studies!

## 1. What is the Iodine Clock Reaction?

The Iodine Clock Reaction is a chemical reaction that involves the formation of iodine molecules from iodine ions and the subsequent reaction of these molecules with a colorless solution, resulting in a sudden change in color.

## 2. What causes the sudden color change in the Iodine Clock Reaction?

The sudden color change in the Iodine Clock Reaction is caused by the formation of iodine molecules, which have a brown color, from iodine ions, which are colorless. This reaction is typically triggered by the addition of a specific reactant, known as the "trigger" or "clock" reactant.

## 3. What factors affect the rate of the Iodine Clock Reaction?

The rate of the Iodine Clock Reaction can be affected by a variety of factors, such as temperature, concentration of reactants, and the presence of catalysts or inhibitors. Additionally, the type of reactants used and their relative proportions can also impact the rate of the reaction.

## 4. What is the purpose of using the Iodine Clock Reaction in experiments?

The Iodine Clock Reaction is commonly used in experiments to study reaction kinetics, or the rate at which a reaction occurs. It can also be used to demonstrate concepts such as reaction mechanisms and the effects of different factors on reaction rates.

## 5. Are there any real-world applications of the Iodine Clock Reaction?

Yes, the Iodine Clock Reaction has several real-world applications, such as in industrial processes for monitoring reaction rates and in medical diagnostics to measure the concentration of certain substances in blood or urine samples. It is also used in chemical demonstrations and experiments in educational settings.

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