Investigating Chemical Equilibrium

Objectives

1. To recognize the macroscopic properties of five chemical systems at equilibrium 2. To observe shifts in equilibrium concentrations as stresses are applied to the systems. 3. To observe a shift in equilibrium concentrations associated with changes in temperature. 4. To explain the observations obtained by applying Le Chatelier’s principle.

Materials

Refer to page 209 of Heath Chemistry Laboratory Experiments.

Procedure

Refer to pages 209 – 211 of Heath Chemistry Laboratory Experiments.

Data and Observations

Part I: Equilibrium Involving Thymol Blue

Table 1 Reagent Added | Stress (Ion Added) | Colour Observation | Direction of Equilibrium Shift | NaOH (Step 5) | OH⁻ | Green | Left | NaOH (Step 6) | OH⁻ | Blue | Left | HCl (Step 3) | H⁺ | Green | Right | HCl (Step 4) | H⁺ | Yellow | Right |

Part II: Equilibrium Involving Thiocyanatoiron (III) Ion

Table 2 Reagent Added | Stress (Ion Added) | Spectator Ion | Observation | Direction of Equilibrium Shift | KCl | None | K⁺, Cl⁻ | No Change | No Change | Fe(NO₃)₃ | Fe³⁺ | NO₃⁻ | Solution Darkens | Right | KSCN | SCN⁻ | K⁺ | Solution Darkens | Right | NaOH | OH⁻ | Na⁺ | Solution Lightens ppt. | Left |

Part III: Equilibrium Involving Cobalt (II) Complexes

Table 3 | Stress | Colour Observation | Direction of Equilibrium Shift | Step 3 | H₂O Increases | Light Red | Left | Step 4 | Heat (Increase Temperature) | Dark Purple | Right | Step 5 | Cool (Decrease Temperature) | Light Red | Left |

Part IV: Equilibrium Involving Chromate and Dichromate Ions

Table 4 Steps 2 and 3 | | 0.1M K₂CrO₄ | 0.1M K₂Cr₂O₇ | | Initial Colour | Yellow | Orange | | 1M NaOH Added | Yellow | Yellow | | 1M HCl Added | Orange | Orange | Step 4 | | 0.1M K₂CrO₄ | 0.1M K₂Cr₂O₇ | | Initial Colour | Yellow | Orange | | 1M HCl Added | Orange | Orange | | 1M NaOH Added | Yellow | Yellow |

Part V: Equilibrium Involving Copper (II)