Experiment 15: Equilibrium Studies

Experiment 15
Title:
Equilibrium studies
Objective:
1. To study the effect of concentration and temperature changes on equilibrium.
2. To predict the direction of the net reaction in an equilibrium system by Le Chatelier’s principle.
Results:
Part 1 (a): Effect of temperature changes on equilibrium
Cu(NO3)2 (aq) Cu(NO3)2 (s)
The color of the solution = dark blue with precipitate

When placed in water bath 60oC

When placed in ice bath

The level of the solid

Decreases

Increases

Color of the solution

Dark blue with precipitate

Dark blue with precipitate

Part 1 (b): Investigate the aqueous equilibrium of a cobalt complex
[Co(H2O)6]2+ + 4Cl- [CoCl4]2- + 6H2O

Original color of the solution

Pink

Color when placed in water bath

Purplish blue

Color when placed in ice bath

Pinkish

Part 2 (a): Effect of concentration changes on equilibrium
2CrO42- + 2H+ Cr2O72- + H2O

Original color of potassium dichromate

Orange

Original color of potassium chromate

Yellow

Color after adding HCl to potassium chromate

Dark yellow

Color after adding NaOH to potassium chromate

Yellow

Color after adding back HCl to potassium chromate

Remains as yellow

Part 2 (b): Thymolphthalein equilibrium
Hln H+ + ln-
Color of the solution changes from blue to colorless
Time taken = 36.1s
Part 2 (c): Ammonium ion / ammonium equilibrium
NH3 + H2O NH4+ + OH-

Initial color of NH3

Colorless

Color after adding phenolphthalein

Purple color

Color after adding NH4Cl

Colorless

Questions and Answers:
1) Write down the equilibrium constant expression for the following reaction:

[Co(H2O)6]2+ (aq) + 4Cl- (aq)  [CoCl4]2- (aq) + 6H2O (l)

In which direction will the equilibrium shift if you (a) increase the concentration of [Co(H2O)6]2+ and b) decrease the