International University, Vietnam National University - HCMC GENERAL CHEMISTRY LABORATORY
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REPORT
EXPERIMENT 4: CHEMICAL EQUILIBRIUM
Group: ____3______ Section: ___4______ Date: ___13/11/2014____
Group members: ____Đặng Thị Lệ Hằng________
____Ngô Hoàng Huân_______
____Lê Thị Thùy Hương_____
_______________________________
Score:__________
International University, Vietnam National University - HCMC GENERAL CHEMISTRY LABORATORY
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1. ACID/BASE EQUILIBRIA
Equilibrium System: 2CrO42 + 2H+(aq) Cr2O72
+ H2O(l)
Descriptio n of conditions
Predicted outcome
Observation Explanation
Init ...view middle of the document...
However, in solution these ions are actually in equilibrium as indicated by the equation:
2 CrO42-(aq) + 2 H+ (aq) Cr2O72-(aq) + H2O (l) Although in the initial solution contains some Cr2O72- , this mount is a little bit so the predominant color will be yellow.
Add Concentrated hydrochloric acid
From Le Chatellier's principle, we know the reaction will try to remove some of the H+ we have added. Adding an acid will increase the concentration of H+ ions in the equilibrium system, forcing the equilibrium to shift to the right, or products ide. This is demonstrated by the solution becoming orange.
The addition of NaOH in test tube The addition of NaOH ties up the H+ ions thereby lowering the concentration of H+. From Le Chatelier's principle, we know the reaction will try to restore some of the H+ we have removed. Therefore, the equilibrium of reaction shift to the left, or reactant side and resulting the more formation of the yellow CrO42-.
International University, Vietnam National University - HCMC GENERAL CHEMISTRY LABORATORY
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2. EQUILIBRIA OF ACID/BASE INDICATORS
Equilibrium System:H(MV)(aq) + H2O(l) H3O+(aq) + MV (aq)
Addition Predicted outcome
Observation Explanation
None
(control) Violet
solution Blue-Violet
solution
When dissolved in water, methyl violet does not dissociate 100% in solution, so the solution contains both H(MV) and MV- ,so the color of this solution is the mix of a litle bit blue and violet. H(MV)(aq) + H2O(l) H3O+(aq) + MV
(aq) (blue) (violet)
6 M HCl
Solution expected to
turn blue
Blue-violet solution
switch to deep blue solution
Adding HCl raise the concentration of H+, the equilibrium shift to left in order to try offset this stress. Thus, the blue-violet solution switch to deep blue solution.
6 M NaOH
Solution expected to turn violet
The deep blue solution
transfuse violet solution
In this case, the stress applied to the equilibrium system is in an decrease in the concentration of H+. NaOH give OH- which react completely with H+ to form water, so the H+ in the solution is neutralized, the equilibrium shift to right to try reforming H+. As the result, the color of solution change from deep blue to violet.
6 M HCl Solution
expected to turn blue
The violet solution turns back to light blue solution
In this case, addition 6M HCl provide H+ in the solution. Because the H+ excess in the solution, By the Le Chateliers Principle, the equilibrium position would shift to the left so as to offset this stress. This lead to the violet solution turns back to blue solution
Comment: The reaction equilibrium of the indicator methyl violet is effected by the change in concentration of H+. If a significant H+ is added, the reaction equilibrium will shift to the left to use up the extra H+. If OH- ions are added to the solution, the reaction equilibrium will shift to the right and the violet form will dominate.
Add 4 drops of 6M HCl
Add 5 drops of 6M NaOH
Add 2 drops of 6M H...
