Question

Lab Experiment 8 Equilibrium II – Le Chatelier’s Principle

Part A ? Lead Compounds Given:

Pb2+  +  2 I ?   ?  PbI2

Pb2+  +  2 OH?   ?  Pb(OH)2

2. Describe the change observed when sodium hydroxide is added in step b (step b. Add enough 0.1M NaOH to cause a change.  Swirl/stir to mix thoroughly) and explain why this change is consistent with Le Chatelier's principle. {Note – to explain in terms of Le Chatelier’s principle means to explain the new change in conditions (in terms of the relative amounts of substance on both sides of the reaction equilibrium), what direction the equilibrium possibly shifted (toward left/reactants or right/products), and how this shift is done in terms of appearance/disappearance of substances.  If more than one equilibrium state is affected explain all conditions and shifts.}

3. Describe the change observed when nitric acid is added in step c and explain why this change is consistent with Le Chatelier's principle.

Answer 1

Sol:-

Le-Chatelier's Principle :- This Law states that if any kind of change in Temperature , concentration or pressure is imposed on the system in equilibrium , then equilibrium shifts in the direction that tends to undo the effect of change imposed.

Given :-

Step (a) Pb²⁺ + 2 I^- <-------------> PbI₂

Step (b) Pb²⁺ + 2 OH^- <-------------> Pb(OH)₂

2. Ans :- Addition of 0.1 M NaOH in (b) step shifts the equilibrium in forward ( i.e products side ) .

Explanation :-

According to the Le-Chatelier's Principle increase the concentration of any one of the reactant species or decrease the concentration of any one of the products species will shifts the equilibrium in the forward direction ( i.e products side ) and vice-versa . Therefore addition of NaOH i.e OH^- in (b) step increases the concentration of OH^- in the reactant side hence equilibrium will shifts in the forward direction .

Also addition of NaOH in (b) step, results in the concentration of reactants disappear while the concentration of products appear with respect to time .

3. Ans :- Addition of HNO₃ in (b) step, shifts the equilibrium in the backward direction ( i.e reactant side) .

Explanation :-

Addition of HNO₃ increase the concentration of H⁺ results in decrease the concentration of OH^- and therefore according to Le-Chatelier's principle equilibrium will shifts in the backward direction .hence concentration of products disappear while concentration of reactants starts appear with respect to time.