Question

1.) The organic solvent phenol, C6H5OH dissociates to a small extent in water according to the following equilibrium equation:

C6H5OH(aq) ⇄ C6H5O - (aq) + H + (aq)

Use Le Chatelier’s principle to predict which form of phenol (C6H5OH or C6H5O - ) will increase in concentration as a result of the addition of HCl.

2) Oxalic acid forms a stable transition metal complex with Fe3+(aq).

Use Le Chatelier’s principle to explain why the addition of oxalic acid to a solution which could be described by the equilibrium reaction below results in a distinct change in color of the solution from bright reddish orange to very pale yellow.

Fe3+(aq) + SCN- (aq) ⇄ [FeSCN]2+(aq) (pale yellow) (colorless) (reddish orange)

Answer 1

according to lechatlier principle, if we disturb the equilibrium of any reaction reaction will re adjust to attain the equilibrium again.

1) C6H5OH(aq) ⇄ C6H5O - (aq) + H + (aq)  

if we add HCl to above reaction concentration of H⁺ will increase in the solution. so reaction will shift to decrease the concentration of H⁺ ions it means backward reaction is favoured. C6H5OH form of phenol will increase.

2) Fe3+(aq) + SCN- (aq) ⇄ [FeSCN]2+(aq) (pale yellow) (colorless) (reddish orange)

by addition of oxallic acid   it forms the complex with Fe⁺² ions in above equilibrium reaction. so concentration of Fe⁺² will decrease, resulting solution looses its bright red colour due to decrease in the concentration of Fe^+2.