Experiment 4: Chemical Equilibrium: Present Well: 1 Point Clear Picture: 1 Point Total 15 Points
Experiment 4: Chemical Equilibrium: Present Well: 1 Point Clear Picture: 1 Point Total 15 Points
Experiment 4: Chemical Equilibrium: Present Well: 1 Point Clear Picture: 1 Point Total 15 Points
Group members:
(total = 100%)
1 Hồ Vũ Duy IEIEIU21095 25
Total = 15 points
I. Abstract
This lab section focused on the subject of reversible reaction. Specifically, various
types of stresses were applied to some certain chemical reversible reaction to examine
the effects. The experiments consist of four main parts. The first two parts focused on
acids and bases with part one tested the equilibria of acid base while part two tested on
the acid and base indicators themselves. Part three worked on reactions that produced
precipitation and the final part focused on the effects of temperature on the prepared
solution.
The data was validated based on Le Chatelier’s principle. The principle announced that
equilibrium can be disturbed if stresses were applied to it, stresses include changes in
Predicted outcomes were given out in advance to this lab section and were then
1. Theory
A reversible reaction is a chemical reaction where the reactants from products that react
together to give the reactants back. Equilibrium point is denoted where the
concentration of the reactants and products will no longer change. A reversible equation
A+B⇌C+D
factors. Le Chatelier’s principle predicted the effects of these factors, they include
changes in concentration, temperature, and pressure. Literature values inferred from
this principle were used for data validation in this lab section.
2. Application
reaction species a change in even single parameter results in the change of equilibrium
3. Experiments
Another purpose for this report was to compare the outcomes of these experiments
predicted solely based on Le Chatelier’s Principle and the real outcomes observed in
the laboratory. The experiments are acid/base equilibria and their indicators, equilibria
Additionally, all equipment was well-prepared in advance, the list of which can be seen
1 Beaker 100mL
2 Beaker 200mL
3 Cylinder 50mL
4 Pipette
8 Ice bath
9 Water bath
10 Stirring rod
(The figures go in order as the table from left to right, upper row to lower row)
1 K2CrO4
2 HCl
3 NaOH
4 Methyl violet
5 CaCl2
6 Na2C2O4
7 H2C2O4
8 NH4OH
9 CoCl2
3.3. Procedure
Equilibrium system:
At first, 30 drops 0.5M K2CrO4 separated 10 drops for each beaker 1, beaker 2, beaker
3 by Pasteur pipette. Then the color of beaker 1 was observed and recorded. Next, 5
drops of concentrated HCl was taken by Pasteur pipette and added to beaker 2. Then
the color of beaker 2 was observed and recorded and compared to beaker 1. Next, 5
drops of concentrated HCl was taken by Pasteur pipette and added to beaker 3. Then
color of beaker 3 was observed and recorded and compared to beaker 1. Then 10 drops
6M NaOH was added to beaker 3 by Pasteur pipette. Then the color was observed and
Equilibrium system:
Then 20mL distilled water was taken by Pasteur pipette, measured by cylinder, and
added to the beaker. Next, the beaker was divided equally into beaker 1 and beaker 2.
The color in beaker 1 was observed and recorded. At beaker 2, 6M HCl was added drop
by drop until no significant change and observed the color change. Similarity, 6M NaOH
was added to beaker 2 drop by drop until no significant change and observed the color
change. Next, 6M HCl was added to beaker 2 drop by drop until no significant change
Equilibrium System:
test tube 1 for this experiment. The color was noted and recorded. After adding 5mL of
0.1M CaCl and 1mL of 0.1M H2C2O4 to test tube #2 with the use of a pipette, the color
was noted, documented, and compared to the color of test tube #l. A pipette was then
used to add 10 drops of 6M HCl, after which the color change was noticed and noted.
Finally, using a pipette, 10 drops of 6M NH4OH were added, and the color shift was
Equilibrium System:
[Co(H2O)6]2+ (aq) + 4Cl− (aq) ⇌ (CoCl4)2− (aq) + 6H2O (l)
pipetted with concentrated HCl dropwise till the solution became purple-violet. If the
system turned a deep blue hue, it meant that there was too much chloride in the
solution. Following that, we have three split test tubes ( the solution from the previous
step was added into 3 test tubes ). The first tube was held at room temperature, the
second in the hot bath, and the third in the cold bath. Following observation, the second
and third tubes were exchanged, placing the second in a cold bath and the third in a
1. ACID/BASE EQUILIBRIA
conditions outcome
(0.5 pts)
turn to orange.
(0.5 pts)
(0.5 pts)
((a): Initial condition, (b): After adding HCl., (c): After adding NaOH)
The color of CrO₄²- wass yellow, and the color of C₂O₇²- was orange.
Based on the predicted outcomes, the outcomes of the performed experiments turned out to be
nearly accurate. The initial solution showed a yellow color of K2CrO4. The solution then turned
into a dark orange color after adding concentrated HCl due to increase of concentration of [H+].
Finally, the solution returned to the yellow color again, almost the same as its initial color due to
Generally, all results were just as expected except for one minor difference in the second phase in
which the color was dark orange instead of dark yellow. This was probably result of excessive
amount of HCl added during this phase, moreover, dark yellow color was predicted based solely
on literature value of theoretical knowledge which do not reflect the result in reality accurately.
The equilibrium equation is: 2CrO₄²- + 2H+(aq) ⇌ Cr₂O₇²- + H2O.
outcome
to dark blue.
(0.5 pts)
change.
(0.5 pts)
of solution unchanged.
(0.5 pts)
((a): Initial condition, (b): After adding HCl., (c): After adding NaOH)
Based on the predicted outcomes, the outcomes of the performed experiments turned out to be
nearly accurate. The initial solution showed a purple color that came from methyl violet. The
solution then turned into a blue color after adding concentrated HCl due to increase of
concentration of [H+] which made methyl violet swift to color that show acidity. Finally, additional
HCl made methyl violet turned back to strong blue once more because of the same reason, more
Generally, all results came out as predicted. It is essential to note that the predicted outcomes were
not specific as they did not state the exact color that the solution might turn out to be, rather, they
just forecast whether the colors might come to a change under the effect of these stresses and in
Predicted
Addition Observation Explanation Equation
outcome
precipitation of CaC2O4.
(0.5 pts)
(aq)
forming of C2O42-
(0.5 pts)
(0.5 pts)
(aq)
According to Le Chatelier’s
precipitate.
(0.5 pts)
(Top left: Test tube 1 – Top right: Test tube 2 after adding H2C2O4
Bottom left: Test tube 2 after adding HCl – Bottom right: Test tube 2 after adding NH4OH)
The direction of equilibrium would depend on the substance (reactants or products) that each time
was added to the reaction.. H2C2O4 was a weak acid so it would dissociate partially. CaC2O4 was
formed slowly because of slow forming of C2O42-. On the addition of HCl, H+ increased. Therefore,
the equilibrium would shift to the left (backward reaction) to reduce the amount of H+. As a result,
less white precipitate formed. According to Le Chatelier’s Principle, the reaction would move to
the right to resstablish the equilibrium. According to Le Chatelier’s Principle, C2O42- increased,
the reaction would move to the right and reduced C2O42-, which also formed more CaC2O4.
Description
Predicted
of Observation Explanation
outcome
conditions
Nothing Light Purple-violet The color of the [Co(H2O)6]2+ solution was pink
changed purple solution changed while the color of (CoCl4)2- was blue. At an
(control) into purple. equilibrium state, the color of the solution was
purple-violet.
(0.5 pts)
Hot water Blue → Purple-violet (room When the solution was put in a hot water bath,
bath Light pink temperature) → the temperature increased. This system was an
pink. It might be
When move into ice-water bath, temperature
different a lot with
decrease, the reaction shift to the left,
Tube 1.
[Co(H2O)6]2+ increase, the solution become
pink.
(0.5 pts)
Light pink Purple-violet (room When the solution was put in an ice-water bath,
Tube 1.
Comment: (0.75 pts)
(4d: After being in cold water - 4e: After being in hot water afterwards)
The real observation is quite similar to the prediction. The color of the [Co(H2O)6]2+ solution is
pink, the color of [CoCl4]2- is blue. When temperature decreased, the equilibrium would be shifted
to the right (forward reaction, which was the exothermic reaction, favored by lower external
temperature) and the [CoCl4]2- increased. When temperature increased, the equilibrium would be
shifted to the left (backward reaction, which was the endothermic reaction, favored by higher
temperature) and the [Co(H2O)6]2+ increased. It was advisable to place the solution test tube in the
hot water and ice bath for enough time and temperature to obtain a relatively accurate result,
V. Conclusions (1 pt)
This lab provided knowledge about Le Chatelier's Principle for the explanation of the changes in
the system and the factors that could affect the reaction system at equilibrium. The chemical system
can be changed under the stresses in concentration, temperature, or pressure. The reaction system
would be shifted until equilibrium has been re-established. Based on the phenomenon, the
equilibrium of the reaction system and its shift can be observed. Through this experiment, it was
possible to rationally explain which direction the reversible reaction would change.
The results performed in this lab were somewhat not up to expected and right to literature value
inferred from Le Chatelier’s Principle. These occurred because of various reasons, mainly due to
human errors. The performers were not professionals in handling equipments as well as handling
chemicals, because of which, many miscalculation and inaccurate amount of chemicas were
applied in this lab. Another reason is that Le Chatelier’s Principle, like many other principles, is
only accurate to a certain extent, it cannot predict all cases with expected results so some
discrepancies between literature value and empirical results are still acceptable in this lab.
Le Chatelier’s Principle is being used worldwide now in numerous industries and manufacturing.
The experiments performed in this lab, however, do not reflect all procedures as well as application
of the principle to industrial levels. It is recommended that further studies and more experiments
should be conducted in order to have a more general view into how Le Chatelier’s Principle is