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Lab 15.3 Testing Le Chatelierès Principle

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by

Victor Lieu

on 19 October 2014

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Transcript of Lab 15.3 Testing Le Chatelierès Principle

Purpose
To test Le Chateliers principle by applying stress to four different chemical equilibria.
Safety
The chemicals used may be corrosive or poisonous, and may cause other toxic effects. Exercise great care when using the chemicals and avoid skin and eye contact. Immediately rinse skin if there is any contact. Ethanol is flammable. Make sure there are no open flames in the lab when using the ethanol solution of cobalt (II) chloride.
Part one: cobalt (II) complexes
1.) Obtain 2mL of the equilibrium mixture with the cobalt (II) chloride complex ions.
2.) Place a small amount of the mixture into each of the five test tubes. Use the fifth as a control (for comparison).
3.) Add drops of water to one test tube until change is evident. Record.
4.) Add drops of 0.2 mol/L silver nitrate to another test tube. Record evidence.
5.) Heat another mixture in a hot water bath. Record evidence.
6.) Cool a mixture in an ice bath. Record evidence.

Part two: Thymol Blue Indicator
Lab 15.3 Testing Le Chateliers Principle
By: Victor. L, Martin. N & Carlin. T
Procedure:
Addition of distilled water
Procedure:
7.) Add 5ml distilled water to each of two small test tubes.
8.) Add 1-3 drops of thymol blue indicator to the water in each test tube to obtain a noticeable colour. Use one test tube as a control.
9.) Add drops of 0.1 mol/L HCl (aq) to the experimental test tube to test for the predicted colour changes.
10.) Add drops of 0.1 mol/L NaOH (aq) to the same tube to test for the predicted colour changes.
Addition of hydrochloric acid
Part Three: iron (III)-thiocyanate equilibrium
Procedure:
11.) Obtain about 20mL of the iron (III)-thiocyanate equilibrium mixture.
12.) Place about 5mL of the equilibrium mixture in each of the three test tubes. Use one test tube as a control.
13.) Add drops of Fe(NO3)3 (aq) to one test tube until a change is evident.
14.) Add drops of 6.0 mol/L NaOH (aq) to this new equilibrium mixture until a change occurs.
14.) Add drops of KSCN (aq) to another equilibrium mixture untill change is evident,
Addition of iron (III) nitrate
Part four: copper (II) complexes
Procedure:
Equation:
16.) Obtain 2mL of 0.1 mol/L CuSO4 (aq) in a small test tube.
17.) Add three drops of 1.0 mol/L NH3 (aq) to establish the equilibrium mixture.
18.) Add more 1.0 mol/L NH3 (aq) to the above equilibrium mixture. Record results.
19.) Add 1.0 mol/L HCl (aq) to the equilibrium mixture from step 18. Record results.
Addition of ammonia
The addition of distilled water droplets to the cobalt (II) complex mixture produced stress on the system. This is because the concentration was changed, and the solution became more dilute and therefore turned pink. Our prediction of a shift to the right and color change to light pink was correct.
Addition of 0.2mol/L silver nitrate
The addition of silver nitrate produced stress which also caused the system to change. The mixture shifted right as predicted, and the color changed to dark pink. Although not seen in the picture, a silver precipitate was also formed. Our prediction of a shift to the right and color change to darker pink was correct.
Heated Bath
By heating the mixture in hot water, the system shifted to the left and turned blue/purple. We predicted a shift to the left because there was an increase in temperature,meaning energy was added. Since energy was on the right side of the equation, if more was added it would need to shift left.
CoCl
4
2-
(alc)
+ 6H O
2
Co(H O)
2
6
2+
+ 4Cl
-
(alc)
(alc)
(alc)
+ energy
H Tb
2
(aq)
H
+
(aq)
+ HTb
-
(aq)
HTb
-
(aq)
H
+
(aq)
+ Tb
2-
(aq)
Ice Water bath
The system shifted right because of the ice water bath, and turned pink. It was a shift to the right because as the system was cooled, energy/heat was lost and the system wanted to make up for the lost energy. Our prediction of a shift to the left was incorrect
The addition of HCl to the thymol blue indicator caused the mixture to turn bright red. The system shifted to the left because by adding HCl, H+ ions were added meaning the system would need to shift left to reach equilibrium again. The color changed also occurred because HCl is acidic and thymol blue is an indicator. Our prediction of a shift to the left and color changed to red was correct.
Addition of sodium hydroxide
The addition of sodium hydroxide to the mixture caused a shift to the right, and a color change to blue. This is because adding OH- ions would remove the H+ ions, forcing the system to shift right to balance. The color change was to blue because sodium hydroxide is basic and thymol blue is in a indicator. Our prediction of a shift to the right and color change to dark blue was correct.
Fe
3+
(aq)
+ SCN
-
(aq)
FeSCN
(aq)
2+
Equation:
The addition of iron (III) nitrate caused a shift to the right and a color change to dark red/brown. This happened because adding more Fe3+ ions forced the system to shift right, and a color change to dark red/brown.
Addition of sodium hydroxide
The addition of sodium hydroxide to the mixture caused precipitate to form (not seen in photo).
Addition of Potassium thiocyanate
The addition of KSCN to this system caused a shift to the right and a color change to dark red/brown. Similarly to how adding more Fe3+ ions caused a shift to the right, the addition of more SCN- ions also caused a shift to the right to balance out and a color change to dark red/brown. Our prediction of a shift to the right and color change to dark red/brown was correct.
Cu(H O)
2
4
2+
(aq)
+ 4NH
3
(aq)
Cu(NH )
3
(aq)
4
2+
+ 4H O
2
(l)
The addition of NH3 caused the system to shift right and change to a deeper blue color. There was a shift to the right because more NH3 was added,meaning the system had to shift right to balance out. Our prediction of a shift to the right was correct.
Addition of more ammonia
By adding even more ammonia, the system shifted right and the color stayed the same. There was a shift to the right because the mixture had more NH3 added again, which meant that it had to shift to the right to balance out again.
Addition of hydrochloric acid
The addition of HCl to the mixture did not cause a shift, but caused the color of the mixture to fade.
Equation:
Equation:
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