Question

Cu +2 OH --> Cu(OH)2

Cu+ 6 NH3 -->Cu(NH3)6 add drops of 6 m NH3 until a change is observed.

a) what is happening at the molecular level when NH3 is added? How are the positions of equilibrium affected for both equations 1 and 2? explain.

b) Add drops of 6 M HCl until a change is observed. stir the solution as you add HCL. What will you observe?

c) what is happening at the molecular level when the HCl is added? How are the positions of equilibrium affected for both equations 1 and 2? explain in terms of Le Cgateliers Principle.

Answer 1

Recall Le Chatelier:

First, let us state the Le Chatelier principle which deals with changes in an equilibrium:

The statement is as follows:

If any equilibrium is disturbed, that is, change in conditions such as P,T, concentration, partial pressure, etc.., the system will counterbalance such change in order to favour the system's equilbirium.

• Change in concentration
• Change in pressure
• Change in temperature

a) what is happening at the molecular level when NH3 is added? How are the positions of equilibrium affected for both equations 1 and 2? explain.

Cu + 2OH --> Cu(OH)2

Cu+ 6NH3 -->Cu(NH3)6

NH3 + H2O --> NH4+ + OH-

Adding some NH3, will increase OH- initially, so Cu(OH)2 forms,

The shift in [Cu + 2OH --> Cu(OH)2] favours the right species, since NH3 increases OH- in solution

this also favours slightly the equilibrium of [Cu+ 6NH3 -->Cu(NH3)6] shifts toward the right as well

Solubility of Cu seems to lower

b) Add drops of 6 M HCl until a change is observed. stir the solution as you add HCL. What will you observe?

that is, it becomes more soluble (i.e. Cu(OH)2(s) dissapears and Cu2+ ions form)

c) what is happening at the molecular level when the HCl is added? How are the positions of equilibrium affected for both equations 1 and 2? explain in terms of Le Cgateliers Principle.

Addition of H+ acid, will neutralize OH- in solution, therefore shifts go towards Cu+2 and OH-