We did experiment: Spectrophotometry(Determination of iron with 1,10-Phenanthroline)
It asks me to find the molar absorptivity of the Fe-phenanthroline complex? How do i find it ? please eplain.
A = absorbance. Sometimes this is measured as %T and if that is done then A = log(100/%T)
Then A = ebc where e is the molar absorptivity, b is the cell length in cm and c is the concn in mols/L.
You should have measured a standard somewhere in the experiment. Plug in c for the standard, b for the cell length, the measured A and calculate e.
To find the molar absorptivity of the Fe-phenanthroline complex, you will need the following information from your experiment:
1. Absorbance values (A): Measure the absorbance of the Fe-phenanthroline complex at different known concentrations. The absorbance is generally determined using a spectrophotometer.
2. Concentrations (C): Prepare solutions of known concentrations of the Fe-phenanthroline complex. These concentrations should span a suitable range.
Once you have the absorbance values (A) and concentrations (C) for the Fe-phenanthroline complex, you can use the Beer-Lambert Law to calculate the molar absorptivity (ε).
The Beer-Lambert Law states that the absorbance of a solution is directly proportional to the concentration of the absorbing species:
A = ε * b * C
Where:
- A is the absorbance of the Fe-phenanthroline complex
- ε is the molar absorptivity (also called molar extinction coefficient or molar absorptivity constant)
- b is the path length of the cuvette through which the light passes (usually 1 cm)
- C is the concentration of the Fe-phenanthroline complex in moles per liter (M)
Rearranging the equation, you can solve for ε:
ε = A / (b * C)
To calculate the molar absorptivity, divide the absorbance (A) by the product of the path length (b) and the concentration (C) for each data point. Take the average of these values to obtain the molar absorptivity of the Fe-phenanthroline complex.
Remember to include the units in your calculations to ensure accurate results. The units of molar absorptivity will depend on the units of concentration used in your experiment (e.g., L/mol·cm or M⁻¹·cm⁻¹).