Module 2: Post-Lab Question and Calibration Plot
Ahmed Juma
February 6th, 2022
CHM 2045L-904
1. What is the relationship between absorbance and concentration?
Because of the direct relationship between absorption and concentration, solutions
with higher concentrations absorb more light than those with lower concentrations.
2. Which dilution technique is a more suitable choice for the purpose of creating a
calibration curve? How can you support your answer?
Serial dilution because this technique entails dilution of a solution several times
successively to create a less concentrated solution
3. If a solution is blue-colored, what wavelength of light (in nm) is being absorbed?
4.
The wavelength of light absorbed by a blue-colored solution is 600 nm. This is
consistent with orange being absorbed. We are able to identify the remaining
combination when a wavelength is absorbed.
4. What is being measured in absorption spectra?
A sample's light absorption throughout a range of wavelengths identified by the
electromagnetic spectrum is measured by an absorption spectra.
5. Why is the wavelength of light set at maximum absorbance when making a Beer’s
Law Plot?
Because it has the greatest signal and is therefore less susceptible to variations.
Additionally, if the wavelength is measured on a pick, it has less of an impact on the
absorbance.
6. Which solution is expected to deviate from the straight line in a Beer’s Law plot: the
more concentrated solution, the more dilute solution, or both?
The more concentrated solution is preferable because, at high concentrations,
molecules are closer together and may thus interact with one another. In a Beer's Law
plot, the more concentrated solution will deviate from a straight line more due to this
interaction's effect on absorbance at a particular wavelength.
Module 2: Post-Lab Question and Calibration Plot
Tables of concentration and absorbance:
Table 1: Concentration and Absorbance of the solution with the Serial Dilution.
Concentration (mol/L)
Absorbance
2.50E-04
0.994
1.25E-04
0.97
6.25E-05
0.96
3.13E-05
0.444
1.56E-05
0.31
Table 2: Concentration and Absorbance of the solution with the Parallel Dilution.
Concentration (mol/L)
Absorbance
2.50E-04
0.001
5.00E-04
0.297
7.50E-04
0.568
1.00E-03
0.79
1.25E-03
0.97
Serial Dilution Calibration Curve:
Module 2: Post-Lab Question and Calibration Plot
Parallel Dilution Calibration Curve:
Concentration of Unknown Solution:
Module 2: Post-Lab Question and Calibration Plot
In order to calculate the concentration of the unknown solution we need to use the following
formula:
𝐴 = ε𝐶𝑙 = (𝑦 = 𝑚𝑥 + 𝑏)
By isolating the concentration -what we are looking for- of the absorbing species we obtain
the following:
𝐶 = 𝐴/𝑙ε
From our unknown solution we know that:
➔ The absorbance is 0.822
➔ The path length is 1cm
➔ The molar absorptivity coefficient is the slope
2
For calculation we need to use the one that has the 𝑅 value closest to 1, which is the parallel
dilution.
Then, the equation for the calibration curve of this dilution is
Using the y = mx + b formula, m would mean the slope, which is 749.75. Then, the molar
absorptivity coefficient or the slope of the equation is 749.75 L/mol-cm.
𝐶 = 𝐴/𝑙ε
𝐶 = (0. 822/1)(749. 75)
−4
𝐶 = 6. 162 𝑥 10
𝑚𝑜𝑙/𝐿