The blue complex ion can be formed from the pink hexaaquacobalt(II) ion according to…
CHEMISTRY · Multi-part · A Level · Chemistry · Transition metals and their chemistry · Transition metals and their chemistry
Problem
The blue complex ion CoCl42− can be formed from the pink hexaaquacobalt(II) ion according to the equilibrium
Co(H2O)62+(aq)+4Cl−(aq)⇔CoCl42−(aq)+6H2O(l)
A series of three separate 50mL samples, each initially at equilibrium and identical in composition and temperature, is prepared.
• Sample A: An additional 50mL of distilled water is added.
• Sample B: An additional 50mL of 0.50MNaCl(aq) is added.
• Sample C: An additional 50mL of 0.50M ethylene glycol (a nonelectrolyte that mixes completely with water) is added.
After each addition, the temperature is held constant and the system is allowed to reach a new equilibrium.
(1) Part 1: (a) For each sample (A, B, and C), predict whether the equilibrium will shift toward reactants (pink), toward products (blue), or show essentially no net shift. Summarize your predictions in a clearly labeled table.
(2) Part 2: (b) Justify each prediction in part (a) by referencing both the change in total molar concentration of dissolved particles and any change in concentration of reactant or product ions introduced by the addition.
(3) Part 3: (c) Rank the three samples from the deepest pink color to the deepest blue color after equilibrium is re-established. Explain how your ranking follows from the shifts discussed in parts (a) and (b).
(4) Part 4: (d) Suppose an additional experiment is performed in which 50mL of 0.50MNaNO3(aq) is added to a fourth identical equilibrium sample. Predict the effect on the position of equilibrium and justify whether your reasoning differs from that used for any of the first three samples.