Introduction to Spectroscopy 1 PDF

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General Chemistry 1 Lab Report...

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1 Introduction to Spectroscopy 1

Introduction to Spectroscopy 1: Question 3: Explain the relationship between A and C, using evidence from the simulation. The relationship between A (absorbance) and C (concentration of solution being measured) is directly proportional. As C increases, so does A at the same proportional rate. As can be seen in the graph for Question 4, each wavelength tested exhibited a proportional absorbance increase as concentration levels increased. For example, when tested at 580 nm wavelength, absorbance increased by approximately 0.01 for every 50 mM increase in solution concentration (see Question 4 for graph).

Question 4: Based on Beer’s Law, would you expect the wavelength used to affect your absorbance versus concentration relationship? What did you observe in the simulation? We would not expect wavelength to affect the relationship in that it would remain proportional (A increasing as C increases), but we would expect wavelength to affect what those proportions are. Because different compounds absorbed light better or worse at different wavelengths, it makes sense that there would be a “sensitive” wavelength which is most absorbed by the compound. So, changing the wavelength will change the rate of absorption, but the A to C will remain linearly proportional. This is observed in the graph below. Changing the wavelength from 580nm to 780nm, the linear proportion between A and C is evident, but the proportion changes from 0.01 absorption increase per 50mM concentration increase to 0.1 absorption increase per 50mM increase in concentration.

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Nickle(II) Chloride: Concentration (mM)

Absorbance at Preset Wavelength (433 nm)

Absorbance at 580 nm

0.53 0.8 1.06 1.33 1.6

100 150 200 250 300

Absorbance at of 780 nm

0.01 0.02 0.03 0.04 0.04

0.21 0.32 0.42 0.53 0.63

Calibration Curve of NiCl2 l = 1.0 cm 1.8 y = 0.0053x - 0.004 R² = 1

1.6

Absorbance

1.4

Absorbance at Preset Wavelength (433 nm) Absorbance at 580 nm

1.2 1

Absorbance at of 780 nm

0.8

y = 0.0021x + 0.002 R² = 0.9997

0.6

Linear (Absorbance at Preset Wavelength (433 nm) )

0.4

Linear (Absorbance at 580 nm)

y = 0.0002x - 0.004 R² = 0.9412

0.2

0 0

50

100

150

200

250

300

350

Linear (Absorbance at of 780 nm)

Concentration

Question 5a: Choose a solution and keep concentration and path length constant as you graph the absorbance for different wavelengths. Solution chosen: Cobalt(II) Nitrate (Co(NO3)2) Wavelengths measured range from 380-780nm at 20nm increments

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Absorption Spectrum for Cobalt(II) Nitrate, l = 1 cm, Concentration = 100 mM 0.5 0.45 0.4

Absorbance

0.35 0.3 0.25 0.2 0.15 0.1 0.05 0 350

400

450

500

550

600

650

700

750

800

850

Waveelength (nm)

Question 5b: What is the value for the “preset” wavelength for your solution? Preset = 549nm

Question 5c: Why do you think the “preset” wavelength is the best wavelength to use for this solution? Cobalt(II) Nitrate is most sensitive to this wavelength, and will therefore show the greatest absorbance rate. This is demonstrated on the graph as well....