Question

In a lab experiment where we add NaSCN and Fe(NO₃)₃ together. Give two compounds whose aqeuous solutions would cause the equilibrium to shift to form . 1) More products. 2) More reactants. (DO NOT INCLUDE COMPOUNDS USED IN EXPERIMENT )

Answer 1

A baanced chemical equation of the reaction is,

3 NaSCN (aq) + Fe(NO₃)₃ (aq) Fe(SCN)₃ (s) + 3 NaNO₃ (aq)

1) For more product.

NaSCN (aq) Na⁺ (aq) + NCS- (aq)

and then NCS- (aq) hydrolyzes conjugate acid HSCN which is less reactive with Fe³⁺ in forming Fe(SCN)₃.

This hydrolysis lowers the equilibrium concentration of Fe(SCN)₃.

Hydrolysis of NCS- can be inhibited by providing enough basic medium.

mild aq. NaOH solution can furnish this task.

HO- (aq) + HSCN ^-SCN (aq) + H2O

More [NCS^-], the equilibrium shift in product direction which consumes NCS^- concentration.

2) For more reactant.

Obviously Acidic medium will cause consumption of NCS- ions into NCSH and to replenish [NCS-] more and more Fe(SCN)3 will decompose back.

Addition of aq. HCl can furnish the more reactants.

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