Question

Name Laboratory Instructor Desk REPORT SHEET Chemical Equilibrium: Le Châtelier's Principle 1. Changes in Reactant or Product Concentrations Copper and Nickellons Colors: i caso,(ag) Blue light 4. Nicl₂(ag) Green light [Cu(NH3).1" (aq) Dark Blue clear 5. [Ni(NH)." (aq) Violet light clear 3. After HCl addition blue light After HCI addition Green Icht Clear Explain the effects of NH3(aq) and HCl(aq) on the Cuso, solution in terms of Le Chatelier's principle. and 7. What initially forms as pale blue and pale green precipitates when NH(aq) is added to [Cu(H2O). [Ni(H2O).)" solutions, respectively? B. Cobalt Ions 8. Color of CoCl(aq) Het Pole Dink 9. Color after the addition of HCl(aq) Indigo blue 10. Color after the addition of H 0 the cold a back Pine (Clear) Account for the changes you observed for the cobalt solutions in terms of Le Châtelier's principle.

Please explain as thoroughly as possible. Thank you

Answer 1

CuSO₄ (aq) Cu(NH₃)₄ Ni(H₂O)₆ Cu(H₂O)₆

1. When we have CuSO₄ (aq) , we have following equilibrium,

CuSO₄ (s)  $\rightleftharpoons$ Cu²⁺ (aq)+ SO₄^2- (aq)

While Cu²⁺ (aq) ions are blue, thus blue light color of solution, Cu²⁺ (aq) is present as hexa-aqua complex :

[Cu(H₂O)₆ ]²⁺

When we add NH₃ (aq), we have this equilibrium

[Cu(H₂O)₆ ]²⁺ + NH₃ (aq)  $\rightleftharpoons$ [Cu(NH₃)₄]²⁺ (aq) (Dark blue )+ H₂O  

Addition of Ammonia solution will shift this towards forward reaction to overcome stress of added conc. of NH₃ (aq) till equilibrium is attained as water is already in excess its concentration does not affected. It brigs more Cu²⁺ (aq) from CuSO₄ into solution to overcome Cu²⁺ (aq) conc. stress.

on addition of HCl ,Copper (II) ions react with chloride  ions (Cl^-) to form complex ions :

[Cu(H₂O)₆ ]²⁺ +HCl (aq)  $\rightleftharpoons$ [CuCl₄]^2- (aq) (light blue )+ H₂O  

We can use le Châtelier's principle to explain changes happened as we change the concentration of the ions in solution. Adding more Cl^- will shift the equilibrium to the right, so the solution will become light blue.  Color of (CuCl₂) solutions depends on concentration: when dilute there is a smaller amount of Cl^- so the color is blue. As concentration increases solution becomes more of a light blue colored.

7. When NH₃ (aq) added to [Cu(H₂O)₆ ]²⁺ and [Ni(H₂O)₆ ]²⁺ initially pale blue and pale green precipitates :

Since NH₃ (aq) is present as NH₄OH (aq) , which gives Hydroxide ions (OH^-), forms complex with Cu²⁺ and Ni²⁺ which precipitates ; as it is insoluble;

Cu²⁺ (aq) +OH^- (aq)  $\rightleftharpoons$ [Cu(OH)₂] (s) pale blue ppt

Ni²⁺ (aq) +OH^- (aq)  $\rightleftharpoons$ [Ni(OH)₂] (s) pale green ppt

It later dissolves back when sufficient amount of  NH₃ (aq) added, as pr le Châtelier's Principle.

8. Color of   CoCl₂ (aq) is pale pink , due to [Cu(H₂O)₆ ]²⁺ , as we have following equilibrium:

CoCl₂ (aq) or [CoCl₄]^2- (aq)  $\rightleftharpoons$ [Co(H₂O)₆ ]²⁺  (aq) (light pink) + 2 Cl^-  (aq)

Due to littile conc. of Cl^- it is not able to form complex with Co²⁺, abundance of water molecules shift equilibrium in favour of [Co(H₂O)₆ ]²⁺ .

After addition of HCl(aq) conc. Cl^- shifts equilibrium in backward direction, to overcome applied stress as per le Châtelier's Principle, thus indigo blue clor is due to [CoCl₄]^2- (aq) .

After addition of more water color again goes back to light pink, as applied stress will be overcome by shifting equilibrium in favour of [Co(H₂O)₆ ]²⁺, thus again light-pink color.