Question

Based on your observations following the addition of (a) Fe(NO₃)₃, (b) NH₄SCH, (c) SnCl₂, (d) AgNO₃, (e) Na₂HPO₄, and (f) NH₃, which way did each of these reagents causethe equilibrium to shift? Considering Le Chatelier's Principle, provide a chemical explanation for the direction of the shift in each case.

Answer 1

Fe(SCN)²⁺(aq)    Fe³⁺(aq) + SCN^-(aq)

(a). Fe(NO₃)₃ - Adding Fe(NO₃)₃ to the reaction increases the concentration of Fe³⁺ ions. Thus according to the Le Chatelier's Principle, the reaction shifts to the left side.

(b). NH₄SCN - Adding NH₄SCNto the reaction increases the concentration of SCN^- ions. Thus according to the Le Chatelier's Principle, the reaction shifts to the left side.

(c). SnCl₂ - Suppose there is some amount of AgCl is present in the solution.

Adding SnCl₂ will precipitate the silver metal reducing the concentration of Ag⁺ ions. Thus according to the Le Chatelier's Principle, the reaction shifts to the right side.

(d). AgNO₃ - Addition of AgNO₃ will produce more Ag⁺ ions in the solution. Thus according to the Le Chatelier's Principle, the reaction shifts to the right side.

(e). Na₂HPO₄ - Adding Na₂HPO₄ to the solution will increase the HPO₄^2- ion concentration. The amount of dissociation must decrease. Thus according to the Le Chatelier's Principle, the reaction shifts to the left side.

(f). NH₃ - Adding NH₃ to the solution will increase the NH₄⁺ ion concentration. The amount of dissociation must decrease. Thus according to the Le Chatelier's Principle, the reaction shifts to the left side.