Equilibrium Lab

Julie Nguyen
Equilibrium Lab
4-28-14

I. Purpose

To study the affect of temperature & concentration changes on systems in equilibrium

II. Safety

Wear apron
Wear goggles
Do not spill chemicals
Clean up after use
Wash hands
Chemicals are TOXIC (by Britney Spears)

III. Procedure
A. Iron-thiocyanate equilibrium
Pipet .3mL of 1 M iron (III) nitrate and .3 mL of 1 M ammonium thiocyanate. into clean 250 mL beaker. Add 75 mL of DS water. Mix well. Divide the solution into equal portions into four 6 inch test tubes. Number the test tubes (1-4). To tube 1, add 5 drops of DS water. Stopper this tube and invert it several times to mix it. Use this tube for as the control. To tube 2, add 5 drops of 1 M iron (II) nitrate. Put a cork stopper in tube and mix it by inverting it. Record color change. To tube 3, add 5 drops of 1 M ammonium thiocyanate. Mix. Record color change. To tube 4, add 5drops of 1 M ammonia solution. Mix. Record color change.
B. Calcium oxalate equilibrium
Put 5 mL of .1 M calcium chloride and 5 mL of .1 M sodium oxalate into 6 inch test tube. Mix by stoppering and inverting. Equilibrium is established by formation of white precipitate. Add concentrated HCl. Shake after each drop. Record any changes.
C. Cobalt chloride equilibrium
Heat 2 mL of saturated aqueous solution of cobalt chloride to boiling in a 6 inch test tube. Record the color before heating. Now place tube in ice water and record any color change.

IV. Data and Observations

A. Iron (III) thiocyanate equilibrium
Color of control: blood red
Color of 2: darker red
Color of 3: darker red
Color of 4: lighter red

B. Calcium oxalate equilibrium
Change observed: became clear after 3 drops of HCl
C. Cobalt (III) chloride equilibrium
Color before: fruit punch red
Color after: plum red/ condensation was blue
Color upon cooling: fruit punch red

V. Postlab Questions

1. Fe in the presence of hydroxide ions forms an insoluble gelatinous precipitate. Did this happen when you added the ammonia solution to the system? How do you know?
Yes, there was a change in the color.
2. How did this affect the equilibrium?
It changed the concentration by shifting it to the right & turning the color darker.
3. Oxalic acid is a weak acid. Can you explain briefly why calcium oxalate dissolves more when HCl is added to that system?
When there was something added to the left side, it causes a shift to the right because of the increased amount. Therefore, causing an decrease in its concentration will cause more calcium to dissolve.
4. IF you were given that cobalt chloride ion is blue, how does heating alter the third equilibrium? Do you think the reaction is endothermic or exothermic?
If the cobalt ion were blue, it would turn red after heating. The reaction is exothermic because after there was an increase in temperature on the right side, it would shift to the left. Shift to the left=exothermic
5. If a chemical was added to the first equilibrium to be studied causes the color to go from deep red to orange, how has the equilibrium been altered?
Either more base was added to the reactants or there was a decrease in iron causing a shift to the left.
6. If calcium chloride solution were added to the second equilibrium, would you expect an increase in precipitate or a decrease in amount?
The amount of precipitate would increase because the reactant side is getting more and shifting to the product side.
7. How would addition of sodium chloride to the third equilibrium to be studied alter the equilibrium?
The solution would turn bluer. The addition of sodium on the left will cause a shift to the right; increasing the concentration on the product side.

VI. Conclusion

The purpose of this lab was to study the affect of temperature & concentration changes on systems in equilibrium. Le Chatelier’s principle is that shifts in direction occur to reestablish equilibrium positions. This basically means, if there is and increase on one side, it will shift to the other to keep “balance”. In the first part of the lab, when more reactant was added to the solution, the color turned darker due to the shift to the products side. When more product/ base was added to the solution, the color turned lighter due to the shift to the reactants side. In the second part of the lab, calcium chloride and sodium oxalate (base) were added together, a precipitate was formed. When HCl (strong acid) was added, it caused the sodium oxalate to dissolve faster. In the third part of the lab, the cobalt chloride turned blue/plum when heated, but returned to its original dark red color when cooled. It shows how if heat was added, there would be a shift to the right, changing the color. And if heat was taken away, there would be a shift to the left, changing it back to its original color. In this lab, I learned how concentration and temperature changes affected equilibrium

VII. Error Analysis

An error could have included the size of the drops given into the test tubes. This could have made a change less significant/noticeable. This would have affect our results because part a was mainly based on the observation of the physical property, color.