1 a sophisticated uvvisiblenear ir instrument has a

1. A sophisticated uv/visible/near IR instrument has a wavelength range of 185 to 3000 nm.
What are its wave number and frequency ranges?
2. A typical simple infrared spectrophotometer covers a wavelength range from 3 to 15 μm.
Express its range a) in wave numbers b) in hertz
(a) ν =
1
3 µm× 10
– 4
cm / µm
= 3.33 × 10 3 cm –1 to
1
15 × 10 – 4 cm
= 6.67 × 10 2 cm –1
(b) ν = 3.00×10
10
cm s
–1
× 3.333×10
3
cm
–1
= 1.00 × 10
14
Hz to
3.00×10 10 × 6.67×10 2 = 2.00×10 13 Hz
Questions:
1. Why is a solution of Cu(NH
3
)
4
2+ blue?
Lesson 3 BEER-LAMBERT’S LAW
Activity 1

Practice exercises
1. Express the following absorbances in terms of percent transmittance:
B) B) 0.379 C) C) 0.485
2. Convert the following accompanying transmittance data to absorbances:
A) 25.5%
B) 32.8%
3. A solution containing 4.48 ppm KMnO
4
has a transmittance of 0.309 in a 1.00=cm cell at 520
nm. Calculate the molar absorptivity of KMNO
4
.
Lesson 4
HOW THE UV-VIS SPECTROPHOTOMETER OPERATES
Activity 1

A compound X is to be determined by UV/Visible spectrophotometry. A calibration curve is
constructed from standard solutions of X with the following results: 0.50ppm, A- 0.24; 1.5ppm.,
A=0.36; 2.5ppm, A=0.44; 3.5ppm, A=0.59; 4.5ppm, A=0.70. Find the slope and intercept of the
calibration curve (recall lesson in physics or geometry), the standard error in y, the
concentration of the solution of unknown X concentration and the standard deviation in the
concentration of X. Construct a plot of the calibration curve and determine the unknown
concentration by hand from the plot.
1 2 3 4 5
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
Concentration in ppm
Absorbance
Conc. In ppm Measured A
0.5 0.24
1.5 0.36
2.5 0.44
3.5 0.59
4.5 0.70
Unknown 0.50
Regression Equation
Slope 0.115
Intercept 0.1785
Concentration of unknown 2.7957
Error Analysis
Standard error in y 0.017029
N 5
S xx 10
Y bar (avg. absorbance) 0.4660
M 1
Std. deviation in c 0.1628