Colligative Properties & Osmotic Pressure

Bezawit wube

Le Chateliers Principle

Lab Report 2

General chemistry ll _ summer sessin

1. To determine the effect of a change on a system at equilibrium

2. To correlate the observed responses with Le Chateliers principle

Procedure:

Part 1: Le Chateliers Principle

Tap water

Beaker, 50 mL, plastic

Toothpicks

Distilled waterMagnifier, dual

Crushed ice

Coffee spoons

Rubber bandsPencil, marking

Thermometer-in-cardboard-tube

Well-Plate-24

Part I

1. Prepare an ice water bath by partially filling one of the 50-mL beakers from your LabPaq with

tap water and crushed ice. Set aside.

2. Prepare a hot water bath by partially filling the second 50-mL beakers from your LabPaq with

Very hot tap water. Set aside.

3. Using a 24-well plate add 5 drops of 2.0 M MgCl2, magnesium chloride solution to wells C1 and

C2. Add 10 drops to wells C3 and C4.

4. Add 1 drop of phenolphthalein to wells C1, C2, C3 and C4. Stir with a clean toothpick.

5. Add 5 drops of 1.0 M NaOH, sodium hydroxide solution to wells C1, C2, C3, and C4. Stir and

record your observations.

6. Add 1 drop of 6.0 M HCl, hydrochloric acid solution to well C1. Stir and record your observations.

Continue to add HCl drop-by-drop to well C1 until you see a color change. Record your

observations.

7. Add 1 drop of 0.15 M Na2EDTA to well C2. Stir and record your observations. Continue to add

Na2EDTA drop-by-drop to well C2 until you see a color change. Record your observations.

8. Use the marker pencil to label an empty pipet C3. Then, squeeze the pipets bulb, place it

in well C3s solution, and slowly release the bulb to carefully suck up all the mixture from the

well into the bulb.

9. You need to place the pipet bulb from Step 8 into the hot water bath, but it will tend to float.

To avoid this, securely attach the pipet stem to a spoon handle with a rubber band. Then place

the pipet bulb in the water bath with the spoon handle outside of the beaker so as to not

obstruct your observations.

10. Repeat Steps 8 and 9 with a second pipet filled with the mixture from well C4. Place this pipet

into the cold water bath.

11. As the temperature of the mixtures in the pipets changes, record your observations.

12. After about 10 minutes, exchange the pipets in the baths. (Put the pipet from the cold water

bath into the hot water bath and vice versa).

13. Dispose of your solutions by pouring them down the drain with running water. Rinse your 24-

well plate and dry it. Remove the marker pencil marks from the pipets and rinse them well by

sucking up distilled water and squeezing it out. They will be used in the next part, so dry the

pipets as well as possible by squeezing their bulbs repeatedly and tapping the tips on a hard

surface covered with a paper towel

Part II

Again prepare hot and cold water baths as instructed in Part I, Steps 1 and 2.

Note: the reactions in Part II are much more subtle than those in Part I. You may have to wait 30

seconds or longer and look very carefully to observe the reaction and changes taking place! Use

your magnifier to better see the changes.

1. Using a 24-well plate, add 5 drops of NaHSO4 sodium bisulfate solution to wells A1, A2, and

A3. Add 10 drops to wells A4 and A5.

2. Add one drop of thymol blue indicator to each well. Stir with a clean toothpick and record

your observations.

3. Add one drop of Na2SO4 sodium sulfate solution to well A1 and stir with a clean toothpick.

Compare the color of well A1 with that of well A2. Record your results.

4. Repeat Step 3, drop-by-drop, until you see a color change. Record your observations.

5. Add a few crystals of solid NaHSO4 to well A3. Stir with a clean toothpick, wait a while, and

record your observations. Compare the color of well A3 with that of well A2. Record your

observations.

6. Repeat Step 5 until you see a color change. Record your observations.

7. Use the marker pencil to label an empty pipet A4. Then squeeze the pipet bulb, place it in

well A4s solution, and slowly release the bulb to carefully suck up all the mixture into the

bulb.

8. You need to place the pipet bulb from Step 7 into the hot water bath, but it will tend to float.

To avoid this securely attach the pipet stem to a spoon handle with a rubber band. Then place

the pipet bulb in the water bath, with the spoon handle outside of the beaker so as to not

obstruct your observations.

9. Make sure the water bath is as hot as possible. If the water bath is not very hot the expected

color change may be difficult to see. Place the pipet bulb from step 8 into the hot water bath.

Record the beginning temperature of the hot water bath.

10. Repeat Steps 7 and 8 with a second pipet for the mixture from well A5. Place this pipet into

the cold water bath.

11. Record the beginning temperature of the cold water bath.

12. When you observe changes in the mixtures in the pipets record your observations and the

water bath temperatures.

13. Compare the final solutions to that in well A2 and record your observations.

14. After about 10 minutes exchange the pipets in the baths. (Put the pipet from the cold water

bath into the hot water bath and vice versa.) Record your observations.

15. Dispose of your solutions by pouring them down the drain with running water. Rinse and

thoroughly dry your 24-well plate. Rinse your pipets thoroughly with distilled water. Dry the

pipets as well as possible by squeezing their bulbs repeatedly and tapping the tips on a hard

surface covered with a paper towel.

Question &Answer Part 1

A. Which way should the equilibrium shift when HCl is added? How do your results support you answer?

It should shift to the left because adding any component causes the equilibrium to shift to the opposite side.

B. Which way should the equilibrium shift when Na2EDTA is added? How do your results support your answer?

It should shift to the right because the removal of a component causes the equilibrium to shift to the side from which the component was removed.

C. Is this reaction endothermic or exothermic? How do you know?Part 2

A. Which way should the equilibrium shift when Na2SO4 is added? How do your results support your answer?

It should shift to the left because adding any component causes the equilibrium to shift to the opposite side.

B. Which way should the equilibrium shift when NaHSO4 is added? How do your results support your answer?

It should shift to the right because the removal of a component causes the equilibrium to shift to the side from which the component was removed.

C. Is this reaction endothermic or exothermic? How do you know?ConclusionsAt the completion of this lab in the chemical reaction occurs when reactants are made into products at the same rate

as products revert to reactants. These two opposing changes occur simultaneously. Le Chateliers

principle says that when a system at equilibrium is put under stress it will correct itself to relieve

the stress and reestablish equilibrium. If a chemical system at equilibrium undergoes a change in

concentration, temperature, volume, or partial pressure, the equilibrium will shift to counter the

change and establish a new equilibrium. Frequently, the concept is used to increase the yield of

reactions. By changing concentration, temperature, volume, or partial pressure we can increase

or decrease the yield of products. There are two ways to alter the equilibrium composition of a

reaction and possibly increase the amount of product.