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Ions and equilibrium shift

I'm sorry for posting so man questions, but my teacher didn't explain this section AT ALL, and we have an assignment on it.

1)
Cu(H2O)42+ (aq) + 4NH3 (aq) <---> Cu(NH3)42+ (aq) + H2O (l)

The left side is pale blue, the right side is deep blue.

When this system has more NH3 added, it shifts in favour of the products and turns deep blue. I understand that. Following that, HCl is added. It shifts back to the left and turns pale blue.
I know it has something to do with the HCl reacting and increasing the products, but I don't know exactly what is causing that shift.

I posted another similar question as well.
Thank you for your help.
(edited 9 years ago)
Original post by PatchworkTeapot
I'm sorry for posting so man questions, but my teacher didn't explain this section AT ALL, and we have an assignment on it.

1)
Cu(H2O)42+ (aq) + 4NH3 (aq) <---> Cu(NH3)42+ (aq) + H2O (l)

The left side is pale blue, the right side is deep blue.

When this system has more NH3 added, it shifts in favour of the products and turns deep blue. I understand that. Following that, HCl is added. It shifts back to the left and turns pale blue.
I know it has something to do with the HCl reacting and increasing the products, but I don't know exactly what is causing that shift.

I posted another similar question as well.
Thank you for your help.


The hydrochloric acid reacts directly with the ammonia from the left side of the equilibrium, removing it from the equilibrium system. This causes the system to move to the left hand side restoring the value of kc and consequently the concentration of the tetraammine complex decreases.

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