Name: _Rimaz Malik___________________________________________
Lab Report: Beer-Lambert Law
Pre-lab Questions:
1. What is the equation for the Beer-Lambert law? Define each term:
The equation for the Beer-Lambert Law is defined as “A= εlc”, where “A” is absorbance, “ε” is
molar absorptivity with units of L mol^-1 cm^-1 (also known as the extinction coefficient). “l”
is defined as the path length of the sample, usually in centimeters. “c” is defined as the
concentration of the compound, and is expressed in mol L^-1.
2. How do you make 100.00 mL of 0.25 M CuSO4•5H2O solution from solid
CuSO4•5H2O? Be specific, including the exact glassware and weight of
CuSO4•5H2O needed:
Cu molar mass = 63.546 g/mol, SO4 molar mass = 96.06 g/mol
CuSO4 molar mass = 63.546 + 96.06 = 159.606 g/mol
H2 molar mass = 2.01588 g/mol * 5 = 10.0794 g/mol, O molar mass = 15.999 * 5 = 79.995
g/mol.
5H2O molar mass = 90.05 g/mol
CuSO4 * 5H2O molar mass = 249.5 g/mol.
0.25 M / 0.1 L = 0.25 mol.
249.5 g/mol * 0.025 mol = 6.2375 of CuSO4*5H2O.
3. You have 100.00 mL of 0.25 M CuSO4•5H2O stock solution. How would you make
10.0 mL dilutions of different concentrations using this solution?
10 ml of dilutions of the solutions can be made via the following chart:
Solution
1
2
3
4
5
6
7
8
9
10
Volume of 0.25 M
CuSO4*5H2O (ml)
10
9
8
7
6
5
4
3
2
1
Volume of water (ml)
0
1
2
3
4
5
6
7
8
9
Results: (neatly show all calculations, including all units)
Compound used: CoCl2.6H2O
Concentration of prepared stock solution: 0.25 M
Calculations for the prepared stock solution (#1): 0.1 L * 0.25 M = 0.25 mol of CoCl2 * 6H2O
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Name: _Rimaz Malik___________________________________________
Experimental max:
The experimental max is 510 nm giving an absorbance of 0.303.
Calibration Curve Data:
Solution #
Absorbance
M
1
2
1.153
0.910
0.25
0.20
3
4
5
0.511
0.197
0.130
Unknown
0.486
0.125
0.0625
0.05
0.1094
Unknown’s True
0.1094
Concentration
Attach Excel graph for calibration curve, set y-intercept set to 0, and show linear equation.
(Absorbance level at varying concentrations (M) of CoCl2* 6H2O solution)
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Name: _Rimaz Malik___________________________________________
The equation of the best fit line is y=4.4402x.
Calculations for the prepared diluted solutions:
Solution #2: C1V1=C2V2
Where V1 = The volume of the stock solution needed to make the new solution.
C1 = Concentration of stock solution.
V2 = Final volume of new solution.
C2 = Final concentration of new solution.
For 0.20 M of concentration: 0.25M * (x) * ( 0.10 ml),
Therefore, x=8
Thus, 8 ml of CoCl2 * 6H2O solution was added along with 2 ml of water to dilute the solution,
making it a 0.20 M concentration.
Solution #4:
For 0.0625 M of concentration:
0.25 * (x) = 0.0625 M * (0.10 ml),
Therefore, x=2.5.
2.5 ml of the CoCl*6H2O solution is added with 7.5 ml of water to dilute the solution, making it a
0.0625 M solution.
Solution #3:
For 0.125 M of concentration,
0.25 M * (x) = 0.125 M * (0.10 ml),
Thus, x=5.
So, 5 ml of the CoCl2 * 6H2O solution is added with 5 ml of water to dilute the solution, making it a
0.125 concentration.
Solution #5:
0.25 M * (x) = 0.05 M * (0.10 ml),
Thus, x=2.
So, 2 ml of the CoCl2*6H2O solution is added with 8 ml of water to dilute the solution, making it a
0.05 M concentration.
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Name: _Rimaz Malik___________________________________________
Determination of  for metal ion:
a. Calculated from graph, slope of line:
y=4.4402x
Slope of line = 4.4402
= 4.4402 M-1 cm-1
b. Calculated from Beer’s Law:
Concentration of unknown solution:
a. Calculated from graph, slope of line:
y = 4.4402x
0.486 = 4.4402x
0.486/4.4402 = x
x = 0.1094 M
b. Calculated from Beer’s Law:
A = ()(l)(c)
A/(l) = c
0.486 / (5.14 )*(1) = 0.0946 M
c. Percent error for each (a. and b. above):
Error = 0.1094 – 0.0946 / 0.1190 = 13.57%
Discussion: (compare transition metal ion concentration in unknown solution obtained by the two methods, and justify which of
the two methods you think is more accurate, and sources of error.)
Based on this experiment, it can be derived that Beer’s Law is considerably more reliable than the
graph itself. This is because the line equation simply provides a rough estimate of the extinction
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Name: _Rimaz Malik___________________________________________
coefficient value. Thus, it is more accurate to calculate the concentration of the substance utilizing
Beer’s equation.
Conclusions:
The purpose of this examination was to utilize a spectrophotometer to decide the absorbance and
extinction coefficient of an aqueous solution within different focuses, along with recognizing the
centralization of an aqueous solution whose concentration was unknown. The lambda max was
discovered to be 510 nm utilizing the 0.25 M of the CoCl2 * 6H2O solution in the spectrophotometer.
The absorbance esteems discovered for every solution were determined to be 1.153 (0.25 M), 0.910
(0.20 M), 0.511 (0.125 M), 0.197 (0.0625 M), and 0.130 (0.05 M). The solution with an unknown
fixation was found (through the utilization of the spectrophotometer and Beer’s law condition) to
have a grouping of 0.10 M and an extinction coefficient of 5.14 M-1 cm-1. Since the absorption values
did not form a perfect line, the equation of the line was considered an estimation. Values that were
calculated using the equation were also estimations.
References:
Hardesty, J. (n.d.). Spectrophotometry and the Beer-Lambert Law. Plano Collin College
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