Beer\'s Law Simulation Lab Report PDF

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Beer's Law Simulation Lab Report...

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Hieu Pham Lab 5: Beer’s Law Simulation November 5th 2020

Abstract: In this experiment, colorimetry method, the method which is often used for chemical analysis, was used to observe the light absorption by colored solutions using the PhET resource project. Potassium Dichromate (K2Cr2O7) was chosen to be observed and its values of transmittance, absorbance and concentration. After data analysis, the molar absorptivity of K2Cr2O7 was found to be 2941.2 L/mol*cm with the standard deviation of 1644.2, while the range for the literature value of its molar absorptivity are 1445.4 to 4265.8 l/mol*cm1. The large value of standard deviation can be explained by the initial concentration of the solution was 0 uM, and the difference of the first and other values were large as well.

II. Data and Results: XConcentratio

n (M) 0.00E+00

Current (I) 600

2.00E-06

476.4

4.00E-06

378.6

6.00E-06

300.6

I^2

1/I

Log I

0.00166 2.77815 7 1 226957 0.00209 2.67797 9 2 143338 0.00264 2.57818 1 1 90360.3 0.00332 2.47798 6 7 9

Log Io/I 0

360000

0.10017 9 0.19997 1 0.30016 2

Table 1. The ideal simulated data

Concentration vs. Current 700 600

Current (I)

500

f(x) = − 49800000 x + 588.3 R² = 0.99

400 300 200 100 0 0.00E+00 1.00E-06 2.00E-06 3.00E-06 4.00E-06 5.00E-06 6.00E-06 7.00E-06

Concentration (M)

Figure 1. Concentration vs Current

Concentration vs. I^2 400000 350000 300000

f(x) = − 44626896000 x + 339044.51 R² = 0.96

I^2

250000 200000 150000 100000 50000 0 0.00E+00 1.00E-06 2.00E-06 3.00E-06 4.00E-06 5.00E-06 6.00E-06 7.00E-06

Concentration(M)

Figure 2. Concentration vs. I2

Concentration vs. 1/I 0 0

f(x) = 276.11 x + 0 R² = 0.99

0

1/I

0 0 0 0 0 0.00E+00 1.00E-06 2.00E-06 3.00E-06 4.00E-06 5.00E-06 6.00E-06 7.00E-06

Concentration (M)

Figure 3. Concentration vs. 1/I

Concentration vs. Log I 2.9 2.8

Log I

2.7

f(x) = − 50013.9 x + 2.78 R² = 1

2.6 2.5 2.4 2.3 0.00E+00 1.00E-06 2.00E-06 3.00E-06 4.00E-06 5.00E-06 6.00E-06 7.00E-06

Concentration

Figure 4. Concentration vs. Log I

Concentration vs. Log(Io/I) 0.35 0.3

Log(Io/I)

0.25

f(x) = 50013.9 x + 0 R² = 1

0.2 0.15 0.1 0.05 0 0.00E+00 1.00E-06 2.00E-06 3.00E-06 4.00E-06 5.00E-06 6.00E-06 7.00E-06

Concentration (M)

Figure 5. Concentration vs. Log(Io/I) The concentration of the unknown was found to be 8.0*10-6 M at absorbance = 0.4, due to the equation in Figure 5.

K2Cr2O7 Concentration(M ) Absorbance Transmittance Molar absorptivity

Std #1 0 uM

Std#2 68 uM

Std #3 136 uM

Std #4 204 uM

Std #5 272 uM

0.00 100.00% 0

0.25 56.23% 3676.5

0.50 31.33% 3676.5

0.75 17.62% 3676.5

1.01 9.86% 3676.5

Avg. = 2941. 2

Std. Dev = 1644. 2

Table 2. PhET Simulation Data

III. Calculations: -

For the absorbance equal to 0.4, due to the Beer’s Law Plot (Figure 5), the equation is

y = 50014x + 4x10-5, which y is Absorbance, x is concentration Therefore the concentration of unknown at A = 0.4 is : (0.4 – 4*10-5)/50014 = 8.0*10-6 M -

Molar absorptivity from PhET Simulation, Ɛ = Absorbance/(Concentration*Path length) = 0.25/(68*10-6(M)*1(cm)) = 3676.5 L/mol*cm At concentration = 0, Ɛ = 0 L/mol*cm Average of molar absorptivity = (3676.5*4 + 0)/5 = 2941.2 L/mol*cm

-

√

(3676.5−2941.2)2∗4 +( 0−2941.2 )2 = 1644.2 5−1 The average molar absorptivity in PhET simulation is much smaller than the slope in the equation in Figure 5. (2941.2 vs. 50014)

Standard Deviation =

IV. References: 1. OCED Library, "UV-VIS Absorption Spectra", https://www.oecdilibrary.org/docserver/9789264069503-en.pdf? expires=1604635907&id=id&accname=guest&checksum=2810976004388B7B263D902AF352 D788. Published 12 May,1981 2. Harris, D. C. Experimental Error. In Quantitative Chemical Analysis, 8th ed.; Freeman, W. H., Ed.; Harper Publishing: New York, 2010; Vol 2, pp. 300-400.

V. Questions: 1. FeCl3 40.0x10-5 M 32.0x10-5 M 24.0x10-5 M 16.0x10-5 M 8.0x10-5 M

Transmittance 17.9 25.0 35.7 50.2 70.8

Absorbance 0.747 0.602 0.447 0.299 0.150

2. a) The molecules of the sample might interact with each other more at higher concentrations, thus the assumption used to derive Beer’s Law breaks down at high concentrations. The effect also leads to a negative deviation from Beer’s Law at high concentration....