Question

Given the following reaction, which is the formation of an iron oxide mineral via hydrolysis:

Fe3+ +3H2O = Fe(OH)3(s) + 3H+

1) Identify the Lewis acids and bases in the above reaction.

2) Define Le Chatelier's principle.

3) Explain how Le Chatelier's principle can be applied to the above reaction. Specifically, how would increasing the pH of the reaction change the relative amount of Fe3+ vs Fe(OH)3?

Answer 1

A Lewis acid is a compound or ionic species which can accept an electron pair from a donor compound.

and A Lewis base is an electron pair donor.

         Fe³⁺ +     3H₂O Fe(OH)₃(s) + 3H⁺

Lewis acid     Lewis base

H₂O molecules donating the electron pair to Fe³⁺ so H₂O is Lewis base & Fe³⁺ is Lewis acid

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(2)Le Chatelier's principle:-

It states that " if a system in equilibrium is subjected to a change of temperature, pressure or concentration, then the equilibrium shifts in such a way that the effect of the changed condition is nullified.

According to the Le-Charterlier's principle,

(1) If the temperature is raised, reaction will proceed in the direction in which some heat can destroy (absorbed) so that temperature of the system remains constant.

Thus increase in temperature shifts the equilibrium in the forward direction of those reactions which proceed with absorption of heat (endothermic reactions), and in the back ward direction of those reactions which proceed with the evolution of heat (exothermic reactions)

(2) If the pressure is increased, reaction will takes place in a direction which will bring about lowering f pressure. This implies that the equilibrium will shifts in the direction which produces the smaller no. of gas molecules.

(3)  If the concentration of reactants is increased or product is removed , the reaction will take place in the forward direction. If the concentration of reactants decreases or increasing the concentration of products the reaction will take place in the backward direction.

(4) Catalyst speeds up both forward & backward reactions to the same extent but does not have any effect on Equilibrium point.

(5)---> When the no. of moles of reactants & products are same the addition of inert gas has no effect

    ----> for a reaction at constant pressure ,addition of an inert gas will shifts the equilibrium in the direction in

            which there is increase in the no . of moles of the gases  

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         Fe³⁺ +     3H₂O Fe(OH)₃(s) + 3H⁺

We know that pH = - log[H⁺]

So [H⁺] = 10 ^-pH

So as pH increases [H+] ion concentration decreases That means the formed product(H+) ion concentration is decreasing thereby we are decreasing the concentration of product, so forward reaction takes place which results in decreasing the amount of Fe³⁺ & increasing the amount of the product Fe(OH)₃