Chemistry Equilibrium Experiment

[Veronica_Oles]

Homework Statement

For this experiment we studied the equilibrium system CuCl_4²⁺(aq) ↔ Cu²⁺ + 4Cl^-(aq) + heat
Net reaction shift is observed by looking at colour changes
-CuCl_4²⁺(aq) become green (shift to left)
- Cu²⁺ is blue and Cl^-(aq) is colourless (shift to right)
What occurs when you put copper (II) chloride solution into an ice bath and a hot bath?
What happens when you had sodium chloride to copper (II) chloride?
What happens when you add silver nitrate to copper (II) chloride?
What happens when you add hydrochloric acid to copper (II) chloride?

Homework Equations

The Attempt at a Solution

I just want to make sure I am understanding what's going on in this experiment. And some guidance for parts I'm unclear of would be greatly appreciated.

What occurs when you put 4 mL copper (II) chloride solution into an ice bath and a hot bath?
During the experiment when the solution was put into a hot bath the solution turned green meaning a shift towards the left. When the solution was put into an ice bath there was no change in colour would that mean that there is no net change in equilibrium, no shift occurring because it did not change colour.

What happens when you had sodium chloride to copper (II) chloride?
When sodium chloride was added to the solution the colour of the solution became lighter. Would this mean that the equilibrium in shifting to the right or is it just because a clear colourless solution was added which diluted the copper (II) chloride solution?

What happens when you add silver nitrate to copper (II) chloride?
When silver nitrate was added to the copper (II) chloride it formed a precipitate, and the colour seemed to appear much paler. Would this mean a shift to the right occurred because you are adding more chloride?

What happens when you add hydrochloric acid to copper (II) chloride?
When hydrochloric acid was added to the solution there was no change the solution remained blue and appeared to be diluted, however I do not think enough acid was used because I'm pretty sure it should have been green.

 

[Borek]

Your answers are a bit chaotic and contain small mistakes which - if the text is taken literally - make them nonsensical.

What occurs when you put 4 mL copper (II) chloride solution into an ice bath and a hot bath?
During the experiment when the solution was put into a hot bath the solution turned green meaning a shift towards the left. When the solution was put into an ice bath there was no change in colour would that mean that there is no net change in equilibrium, no shift occurring because it did not change colour.

I think you are missing an "If" somewhere here. If so, you are right.

What happens when you had sodium chloride to copper (II) chloride?
When sodium chloride was added to the solution the colour of the solution became lighter. Would this mean that the equilibrium in shifting to the right or is it just because a clear colourless solution was added which diluted the copper (II) chloride solution?

There is not enough information to say (although increasing Cl^- concentration should in general shift the equilibrium to the left). Differentiating between color getting weaker because of dilution and changing hue is often very difficult. Have you tried comparing the sample after NaCl addition to the sample of the original solution?

What happens when you add silver nitrate to copper (II) chloride?
When silver nitrate was added to the copper (II) chloride it formed a precipitate, and the colour seemed to appear much paler. Would this mean a shift to the right occurred because you are adding more chloride?

Again, "paler" seems to be referring to the dilution effect, not the hue change. And you are not adding more chloride, quite the opposite.

What happens when you add hydrochloric acid to copper (II) chloride?
When hydrochloric acid was added to the solution there was no change the solution remained blue and appeared to be diluted, however I do not think enough acid was used because I'm pretty sure it should have been green.

And the shift to the green is what I would expect in this case.

 

[Delta2]

It is not clear to us whether you add the pure substance or a solution of it. For example when you add NaCI, you add it directly , or first you dissolve NaCl in water and then you add the solution of NaCl to the original solution of CuCl4?

From the looks of it , you add solutions of the substances, that's why you can't make easy conclusions of the shifting of balance. If you have two solutions of volume $V_1$ and $V_2$ and concentration $\rho_1$ and $\rho_2$ then the mixing of these solutions will give a solution with volume $V_1+V_2$ but the concentration will not be $\rho_1+\rho_2$ rather it will be $\rho=\frac{\rho_1V_1+\rho_2V_2}{V_1+V_2}$. So it can be the case (depending on the values of $\rho_1$ and $\rho_2$) that the final concentration $\rho$ is smaller than the original concentration, though you add extra mass(or moles) of the solvent. So it could be the case that when you add the solution of NaCl you actually reduce the concentration of chloride in the final solution. Not to mention what consequence has, this implicit adding of water, to the concentrations of the rest of the elements present.

 

[Veronica_Oles]

Your answers are a bit chaotic and contain small mistakes which - if the text is taken literally - make them nonsensical.
I think you are missing an "If" somewhere here. If so, you are right.
There is not enough information to say (although increasing Cl^- concentration should in general shift the equilibrium to the left). Differentiating between color getting weaker because of dilution and changing hue is often very difficult. Have you tried comparing the sample after NaCl addition to the sample of the original solution?
Again, "paler" seems to be referring to the dilution effect, not the hue change. And you are not adding more chloride, quite the opposite.
And the shift to the green is what I would expect in this case.

Sorry, for the addition of silver nitrate I did not mean to put "adding more chloride"