Date conducted: 2/9/2012
Experiment purpose: To determine the effect of a change on a system at equilibrium and to correlate the observed responses with Le Chatelier’s principle. Experiment Chemical list:
1 Tap water
1 Distilled water
1 Crushed ice
2 Coffee spoons
1 Rubber bands
2 Beaker, 50 mL, plastic
1 Magnifier, dual
1 Pencil, marking
In the Experiment Bag: LeChatelier’s Principle
1 E.D.T.A., .15 M (Na2EDTA) - 2 mL in, Pipet
1 Hydrochloric Acid, 6 M - 2 mL in Pipet
1 Magnesium Chloride, 2 M - 3 mL in Pipet
1 Phenolphthalein Solution, 1% - 0.5 mL in Pipet
2 Pipet, Empty Short Stem
1 Sodium Bisulfate Crystals - 0.5 g in Vial
1 Sodium Bisulfate, 0.1 M - 4 mL in Pipet
1 Sodium Hydroxide, 1 M - 2 mL in Pipet
1 Sodium Sulfate, 1 M - 2 mL in Pipet
1 Thymol Blue Indicator, 0.04% - 0.5 mL in Pipet
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. Precipitation noted. 5. Add 5 drops of 1.0 M NaOH, sodium hydroxide solution to wells C1, C2, C3, and C4. Stir : solution thickens, turns dark pink.residue also formed in the solution. 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. Pink solution turns to milky solution again
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. Color changes to clear.
8. Use the marker pencil to label an empty pipet “C3.” Then, squeeze the pipet’s bulb, place it in well C3’s 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. Cloudy pink solution observed. 10.Repeat Steps 8 and 9 with a second pipet filled with the mixture from well C4. Place © Hands-On Labs, Inc. LabPaq CK-2 68
this pipet into the cold water bath. Still fuschia pink color 11.As the temperature of the mixtures in the pipets changes, C3- cloudy light pink, C4- fuchsia pink 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). C3-fuschia pink in the hot water bath and C4 – turns to cloudy pink. 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. Questions:
In Part I the reaction you observed was Mg(OH)2 (s) Mg2+ (aq) + 2 OH- (aq). Compare the colors you observed in the experiment and answer these questions: A. Which way should the equilibrium shift when HCl is added? How do your results support your answer? The purple solution changed to milky shifting to the right because of the chloride ion. B. Which way should the equilibrium shift when Na2EDTA is added? How do your results support...