How do I Calculate the concentration of iron(lll) with absorbance measurement. Wavelength is 480nm, solution is 1 ml FeCl3 : 9ml HCl, absorption is .250A, concentration of stock FeCl3 solution is 0.00050M and stock HCl solution is 2.0M. I not sure how to use beer's law to find the concentration of the iron(lll) or is there a different equation I should be using?
Did you have a standard concn of Fe and you have an absorbance for that? Or do you the the absorptivity or extinction coefficient?
No. I'm doing the questions in my lab manual and this is all the information I have. The lab is spectroscopic analysis of spinach. Test tube 1 has 9ml of 2.0M HCl and 1 ml of .00050M FeCl3 and 10ml of KSCN. But question asks for the concentration of iron lll before the KSCN is added. The KSCN is 100 ml of a 1.5M solution which had a mass weight if 14.578g. The mass of the spinach was 5.05g and the spinach extract was .413 absorption.
did you manage to solve this?
To calculate the concentration of iron(III) using absorbance measurements, you can indeed use Beer's Law, which is the equation used to relate the concentration of a chemical substance in a solution to the amount of light absorbed by the substance. Beer's Law is expressed as:
A = εcl
Where:
A = Absorbance
ε = Molar absorptivity (also known as the molar extinction coefficient)
c = Concentration
l = Path length (the distance traveled by light through the solution)
In your case, you have the absorbance (A = 0.250) and the wavelength (480nm). However, the molar absorptivity (ε) for iron(III) at 480nm is required for further calculations.
1. Determine the molar absorptivity (ε) for FeCl3 at 480nm:
The molar absorptivity is a constant provided by experimental data or available in reference sources. If you have access to a reliable source, such as a scientific literature database or a chemistry handbook, you can find the molar absorptivity value for iron(III) at 480nm.
2. Calculate the concentration (c) of the iron(III) solution:
Rearrange Beer's Law equation to solve for concentration (c):
c = A / (ε * l)
Given:
A = 0.250
ε = molar absorptivity at 480nm (for FeCl3)
l = path length
3. Calculate the path length (l):
Since the solution volume for the absorbance measurement is 1 ml, we assume the path length is equal to 1 cm.
l = 1 cm
4. Calculate the concentration (c):
Substitute the known values into the equation:
c = 0.250 / (ε * 1 cm)
Note: Ensure that the units of absorbance and path length are compatible with the molar absorptivity value.
5. Calculate the final concentration, taking into account the dilution factor:
The provided solution is a mixture of 1 ml FeCl3 and 9 ml HCl. Therefore, the diluted iron(III) solution is 1/10th of the stock FeCl3 solution.
c_final = c_initial * dilution factor
Given:
c_initial = 0.00050 M (concentration of FeCl3 stock solution)
dilution factor = 1/10
Substitute the values into the equation:
c_final = 0.00050 M * 1/10
By following these steps, you can calculate the concentration of iron(III) in the solution based on absorbance measurements.