Question

G. C. 2-7 Studying the Effect of Changes in Conditions on an Equilibrium System 57 System No. 4: [Co(H0).J? + 4C 5 [CoCLIC + 6H,0 Solutions Observations Dissolved CoCl-6H,0 - Pink solution Solution plus HCI Blue Solution Heated solution Blue Solution Cooled solution Pink Solutam 9. According to the equilibrium equation, which ion(s) do you have after the solid was diluted? Explain how you know the identity of the ion(s) present. 10. Explain what happened when HCl was added to the solution. 11. Explain what happened when the solution was heated. Was the shift in equilibrium exothermic or endothermic? 12. Explain what happened when the solution was cooled. Was the shift in equilibrium exothermic or endothermic? System No. 5: Fe + SCN S[Fe(SCN) (Forward reaction is exothermic) Solutions Observations Fe(NO), + KSCN mixture Diluted solution Pale red Heated solution Land bron Lone Cooled solution No change (red) Solution + Fe(NO3 More red some Solution + KSCN More ved Isame Solution + AgNO, Milky white (AgSON formed) Solution + NaOH Brown forange (Felolls) formed 13. When the test tube was placed in the hot water bath, was the shift in equilibrium endothermic or exothermic? Explain. 14. Explain what happened when you added more Fe(NO), and KSCN. 15. Explain what happened after you added AgNO. Hini: Determine the potential products being formed from adding AgNO, to the solution. 16. Explain what happened after you added NaOH. Hint: Determine the potential products being formed from adding NaOH to the solution,

Answer 1

9. on dilution of CoCl2.6H2O, [Co(H2O)6]2+ ions are present. the identity of ions can be seen by the colour of solution. pink colour confirm the presence of these ions.

10. According to Le Chatelier’s principle, adding additional reactant to a system will shift the equilibrium to the right, towards the side of the products. By the same logic, reducing the concentration of any product will also shift equilibrium to the right. The converse is also true. If we add additional product to a system, the equilibrium will shift to the left, in order to produce more reactants. Or, if we remove reactants from the system, equilibrium will also be shifted to the left.

In this case, if we are adding HCl the we are increasin the concentraion of the reactant ion i.e. Cl- ions in the solution sothe equillibrium shifts to the right and more [CoCl4]2- ions are formed which changethe colour of solution to blue.

11.This is an endothermic reaction. for endothermic reaction we can assume heat as reactant as heat is required by the reaction.

So,according to Le Chatelier,s principle, adding heat causes the equilibrium constant to shift to the right. This, correspondingly, makes the solution blue. the shift in equillibrium to endothermic to neutrallise the extra heat provided.

12. when the solution is cooled, heat is removed (we can say a reactant concentration reduces) so th equillibrium shifts towards left and pink colour appears. the shift in equillibrium is exothermic.

System5

13. This is an example of exothermic reaction so we can assume heat as a product. on heating the solution the equillibrium shifts towards left. the equillibrium shift is endothermic to combat the external heat provided.

14. when more Fe(NO)3 and KSCN are added, the reactant concentration increases so the equillibrium shift towards right and more product is formed resulting in a red colour solution.

15. On adding Ag(NO)3 the Ag+ reacts with SCN- to form [Ag(SCN)]. The equilibrium has shifted to the left, due to removal of SCN- by precipitation. So the color fades, and the solution turns cloudy

Ag+ (aq) + SCN- (aq) = AgSCN (s)

16 Similarly on adding NaOH, Fe3+ react with NaOH to form Fe(OH)3 which shift the equillibrium to left as reactant concentration decreases and turns the colour of solution to brown /orange.