. Le Chatelier’s Principle Procedure steps: Place 50 ml of water in 125 ml Erlen
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Question
. Le Chatelier’s Principle
Procedure steps:
Place 50 ml of water in 125 ml Erlenmeyer flask.
Put one tablet of Phenol red to the water. Record the color immediately.
Start timing while you place the straw into the solution. Then, Start blow bubbles and stop when the color is change.
Add the 5% of ammonia water solution by using the dropper and stop when the color changes to the original starting color.
Repeat steps 3 and 4 as many time as you can and stop when the color is no longer change the equilibrium back to the original starting color.
Do step 1 and 2 again, then run up and down the stairs for three times and then continue to do step 3 , 4 and 6.
Data:
The color after adding one tablet of Phenol red to the water: light pink
Step
Data
Trial 1
Trail 2
(Run up and down the stairs)
4
Time (seconds) for color change.
0:36 s
0:23 s
4
Notes for color change
Light orange
Orange
5
Color change (if any) after one (1) drop of dilute ammonia
Change to light pink than pack to orange
Change to light pink than pack to orange
6
Time (seconds) for color change back
0:13
0:20
7
Number of drops for color to change back
6 drops
9 drops
1.The equilibrium you were stressing can be written simply like this:
Acidic <==> Basic
Indicate the color associated with each side of the equilibrium.
2.Which way was the equilibrium shifted (right or left) when you blew bubbles?
3.Write the balanced chemical equation associated with this. (Hint: Carbonic acid is H2CO3).
4.Which way was the equilibrium shifted when you added the ammonia water?
5.Ammonia water is NH3(aq). Write the balanced chemical equation of the reaction that occurred when you added it.
6.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?
7.Explain chemically why you could not repeat the step indefinitely.
8.Using Le Chatelier's Principle, discuss and explain your results for when you altered the procedure.
Step
Data
Trial 1
Trail 2
(Run up and down the stairs)
4
Time (seconds) for color change.
0:36 s
0:23 s
4
Notes for color change
Light orange
Orange
5
Color change (if any) after one (1) drop of dilute ammonia
Change to light pink than pack to orange
Change to light pink than pack to orange
6
Time (seconds) for color change back
0:13
0:20
7
Number of drops for color to change back
6 drops
9 drops
Explanation / Answer
1. To a solution of phenol red in water which shows a pH lower then 7 when we blew bubbles through it (the equilibrium shifts to the right handside). When we add NH3 the equilibrium shifts to further left hand side.
2. The blowing of bubbles introduces CO2 in solution. Thus the solution turns more basic (pH lower than 7) from starting point and we get a light pink coloration.
3. H2CO3 <==> H+ + H2O + CO2
4. After adding NH3 the equilibrium shifts to the more basic side (pH greater than 7), equilibrium towards right handside.
5. NH3 + H2O <==> NH4+ + OH-
6. Number of drops of NH3 water indicates the basicity level required to reach the end point for the phenol red. The end point to reach this level changes with each trial and the amount of CO2 in solution might differ slightly for each run and thus the net NH3 water required is different.
7. The steps could not be repeated indefinitely as only a certain amount of CO2 can be absorbed by the phenol red aqueous solution.
8. According to LeChatellier's principle If we add more CO2 in solution, the equilibrium for carbonic acid would shift towards reactant end H2CO3 is formed to reestablish the equilibrium. Similarly when we addd a base as NH3 more of H2CO3 would react to form NH4+ and CO2 in solution.
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