Overview
This lab explores the equilibrium between two cobalt complex ions, observing color changes to determine how different stresses affect the reaction and inferring thermodynamic properties.
Cobalt Complex Ion Equilibrium
- Cobalt forms colored complexes with water (pink/red) and chloride ions (blue).
- The equilibrium reaction shifts between these complexes, observable by color changes.
Applying Le Châtelier’s Principle
- Adding hydrochloric acid (HCl) increases chloride ions, shifting equilibrium to form more blue cobalt chloride complex.
- Adding calcium chloride also increases chloride ions, causing a shift toward the blue complex near the salt.
- Adding water dilutes chloride concentration, shifting equilibrium back to the pink cobalt-water complex.
Precipitation and Reaction Shifts
- Adding silver nitrate forms a white precipitate with chloride ions, removing chloride ions from solution.
- The removal of chloride ions shifts equilibrium toward the pink cobalt-water complex (reactants).
Temperature Effects on Equilibrium
- Increasing temperature (using a hot water bath) shifts equilibrium toward the blue cobalt chloride complex (suggests endothermic forward reaction).
- Decreasing temperature (ice bath) shifts equilibrium toward the pink cobalt-water complex (suggesting exothermic reverse reaction).
Key Terms & Definitions
- Equilibrium — A state where the forward and reverse reactions occur at equal rates.
- Le Châtelier’s Principle — When a stress is applied to a system at equilibrium, the system shifts to counteract the stress.
- Complex ion — An ion formed from a metal ion bonded to one or more ligands.
- Precipitate — A solid formed in a solution during a chemical reaction.
- Endothermic reaction — A reaction that absorbs heat.
- Exothermic reaction — A reaction that releases heat.
Action Items / Next Steps
- Record color changes and infer which side of the reaction is favored after each stress.
- Determine whether the forward reaction is endothermic or exothermic based on temperature tests.
- Review solubility rules and Crystal Field Theory for further understanding.