Practical Writeup Experiment 2, Thermodynamics of the Rhodamine B Lactone Zwitterion Equilibrium
AIM:
The aim of the experiment was to determine the enthalpy (ΔH), entropy (ΔS) and Gibbs free energy (ΔG) for the Rhodamine β-Lactone Equilibrium. To accomplish this, a manual spectrophotometer was used to determine the maximum absorbance of a sample of Rhodamine β-Lactone. The absorbance of the sample was then measured over a range of temperatures from which the equilibrium constant (K), enthalpy (ΔH), entropy (ΔS) and Gibbs free energy were then calculated.
INTRODUCTION:
The xanthene dye Rhodamine β-Lactone can undergo multiple equilibria. “In protic solutions, Rhodamine β-Lactone exists as an equilibrium mixture of a colourless lactone and a coloured zwitterions.” [1] as shown in appendix 1. The position of the equilibrium depends on solvent hydrogen-bond donating ability and solvent polarisability [2]. The equilibrium also shifts under an increase in temperature to the less polar lactone. This thermochromic transformation allows for the study of the thermodynamic properties of the equilibrium as it progresses.
PROCEDURE:
Refer to Manual for CHEM 2701: Chemical Reactivity Experiment 2: Thermodynamics of the Rhodamine β-Lactone Zwitterion Equilibrium, pages 28-31.
CALCULATIONS/RESULTS:
The mass of Rhodamine β-Lactone required to make up the stock solution, specified on page 30 of Manual for CHEM 2701: Chemical Reactivity Experiment 2: Thermodynamics of the Rhodamine β-Lactone Zwitterion Equilibrium, was calculated in the following way: * Using the relationship n=CV, the number of moles were calculated using the listed volumes and concentrations. * The required masses were then calculated using the following relationship: n=mMr.
The absorbance at 100% concentration of Rhodamine β-Lactone zwitterion was then calculated using Beer’s Law (A=εbc), in accordance with the manual.
The full calculations can be seen in Appendix 3.
It should be noted here that from the above calculation, A100% was found to be above 1, and as a
The aim of the experiment was to determine the enthalpy (ΔH), entropy (ΔS) and Gibbs free energy (ΔG) for the Rhodamine β-Lactone Equilibrium. To accomplish this, a manual spectrophotometer was used to determine the maximum absorbance of a sample of Rhodamine β-Lactone. The absorbance of the sample was then measured over a range of temperatures from which the equilibrium constant (K), enthalpy (ΔH), entropy (ΔS) and Gibbs free energy were then calculated.
INTRODUCTION:
The xanthene dye Rhodamine β-Lactone can undergo multiple equilibria. “In protic solutions, Rhodamine β-Lactone exists as an equilibrium mixture of a colourless lactone and a coloured zwitterions.” [1] as shown in appendix 1. The position of the equilibrium depends on solvent hydrogen-bond donating ability and solvent polarisability [2]. The equilibrium also shifts under an increase in temperature to the less polar lactone. This thermochromic transformation allows for the study of the thermodynamic properties of the equilibrium as it progresses.
PROCEDURE:
Refer to Manual for CHEM 2701: Chemical Reactivity Experiment 2: Thermodynamics of the Rhodamine β-Lactone Zwitterion Equilibrium, pages 28-31.
CALCULATIONS/RESULTS:
The mass of Rhodamine β-Lactone required to make up the stock solution, specified on page 30 of Manual for CHEM 2701: Chemical Reactivity Experiment 2: Thermodynamics of the Rhodamine β-Lactone Zwitterion Equilibrium, was calculated in the following way: * Using the relationship n=CV, the number of moles were calculated using the listed volumes and concentrations. * The required masses were then calculated using the following relationship: n=mMr.
The absorbance at 100% concentration of Rhodamine β-Lactone zwitterion was then calculated using Beer’s Law (A=εbc), in accordance with the manual.
The full calculations can be seen in Appendix 3.
It should be noted here that from the above calculation, A100% was found to be above 1, and as a