Equilibrium and Thermodynamics Lecture Notes

Overview

• Topic: Equilibrium and Thermodynamics
• Objective: Calculate enthalpy, entropy, and Gibbs free energy of dissolution of borax in water.

Required Equipment

• Burette (for titration)
• 5 ml volumetric pipette (for transferring water)
• Digital thermometer (to measure temperature)

Experiment Objectives

1. Titrate HCl with saturated solutions of borax.
2. Determine the equilibrium constant of dissolution.
3. Study the temperature dependence of Ksp.
4. Plot Ksp vs. Temperature to calculate ΔH, ΔS, and ΔG.

Key Equations

• Equilibrium equation for borax dissolution.
• Gibbs Free Energy equation involving Ksp and temperature.
• Plot: ln(Ksp) vs. 1/T for ΔH and ΔS.

Experimental Procedure

Preparation

1. Test Tubes:

   • Prepare 10 test tubes (2 for each temperature).
   • Use 5 ml of DI water to mark levels on test tubes.

2. Saturated Borax Solution:

   • Dissolve 30g of borax in 150ml of water at ≤50°C.
   • Ensure excess borax for saturation.

3. Sampling Borax Solution:

   • Cool solution to ~45°C.
   • Dispense into test tubes at various temperatures (45°C, 35°C, 25°C, etc.).
   • Use ice baths to cool to necessary temperatures.

Titration

• Indicator: Bromocresol Green (Blue in basic, Yellow in acidic)
• Procedure:
  • Transfer borax solution to flask.
  • Titrate with 0.2 M HCl.
  • Endpoint: Yellow color persists.

Data Collection

• Record initial and final volumes of HCl.
• Calculate moles of borax in solution.
• Use for calculating Ksp.

Calculations

• Ksp Calculation: Use titration results.
• ΔH and ΔS:
  • Slope of ln(Ksp) vs. 1/T gives -ΔH/R.
  • Intercept gives ΔS/R.
• ΔG Calculation:
  • Method 1: RT ln(Ksp)
  • Method 2: ΔH - TΔS

Important Considerations

• Temperature Control: Essential for accurate results.
• Solution Transfer: Avoid transferring solids.

Data Analysis

• Plot ΔG vs. Temperature for both methods.
• Address the impact of changing solution temperatures.

Conclusion and Reporting

• Include sample calculations, data tables, and observations in the lab report.
• Plot ΔG and summarize results.
• Discussion: Answer provided questions.

Tips

• Record temperatures to the nearest 0.1°C.
• Ensure no air bubbles in the burette.
• Understand dissociation processes (e.g., acetic acid vs. HCl).

Final Remarks

• Be mindful of significant figures.
• Prepare for potential questions on the report's content.

Good luck with the experiment!