Question

Step	Data	Trial 1	Trial 2
4	Time (seconds) for color change	08.21	07.28
4	Notes for color change	The starting color of the solution is pink and after that it’s changed to Yellow
5	Color change (if any) after one (1) drop of dilute ammonia	none	none
6	Time (seconds) for color to change back	27.56	28.93
7	Number of drops for color to change back	4	5

1. What does the number of drops of ammonia water indicate? In other words, what is their significance, such as if they were the same for all trials or if they differed?

2.Explain chemically why you could not repeat the step indefinitely.

3, Using Le Chatelier's Principle, discuss and explain your results for when you altered the procedure.

Answer 1

1.

Color change directs us to assume presence of two dyes. Methyl orange and Phenolphthalein.

Methyl orange is yellow in acidic pH and Phenolphthalein is pink at basic pH.

Number of drops of ammonia indicate pH of solution.

If the pH is lower, towards acidic it will take more ammonia water drops to change the color back.

Numbers of drops differed in both trials, means both solutions had different pH.

2.

Any chemical reaction tends to proceed until the rate of the forward reaction becomes equal to

the rate of the reverse reaction. Then the reaction is said to be at equilibrium. Adding or

removing a component will disturb the dynamic balance between two reaction rates.

According to Le Chatelier's principle, any change imposed on a system in dynamic equilibrium will cause

it to shift in the direction that opposes the change.

The system will change back for some limited repetitions but equilibrium will shift to another state than that of before and it will give reduced result or no result at all. As example, less coloration at more drops or more time to change back. Which will tend to increase.

That’s why we cannot repeat the step indefinitely.

3.

Le Chatelier’s principle explain how the position of equilibrium changes when stress is introduced on the equilibrated system.

To alter the procedure, more drops of ammonia water were added to solution. We could easily see that number of drops is directly proportional to the intensity of pink colour.

More number of drops or intense pink color takes more time to change back to yellow.

Also the addition of acid was used to increase the yellow coloration.

It does prove that, system DOES try to resist change and come back to equilibrium.