1. Cu2+ + 4NH3 → Cu(NH3)42+ (deep blue)
? %
White KNO3
? %
Blue CuSO4.5H2O
Cu NH3 → Cu(NH3)42+ (deep blue)
EX8-1 (of 12)

2. A more saturated color means a higher concentration of the colored component
The “saturation” can be determined by measuring the amount of light absorbed by the solution, called its ABSORBANCE
EX8-2 (of 12)

3. A light bulb emits white light A prism separates the colors of light
SPECTROMETER – A device that measures the amount of light absorbed by a sample
A light bulb emits white light
A prism separates
the colors of light
Light passes through the sample
Light passes through a slit to form a narrow beam
Rotating the prism allows just one color to pass
through another slit
A detector measures the final amount of light
EX8-3 (of 12)

4. Concentration of CuSO4.5H2O (%)
If you choose a specific wavelength of light, and measure the absorbances of CuSO4.5H2O solutions of known concentrations, and plot absorbance vs. concentration
, the relation is linear
Absorbance
C: % % % % % A:
Concentration of CuSO4.5H2O (%)
EX8-4 (of 12)

5. If an unknown solution has an absorbance of 0
If an unknown solution has an absorbance of using a wavelength of light of nm, find its concentration of CuSO4.5H2O
= mx + b
m (slope): 1.9
= (1.9 %-1)C
0.350 = (1.9 %-1)C
= C
_________
1.9 %-1
b (Y-intercept): 0.001
= mC + b
= %
m = Δy
____ Δx
= Δ Abs.
__________
Δ Conc.
= no units
___________ %
= %-1
EX8-5 (of 12)

6. USING THE SPECTROMETER
Place a colorless solution (called the BLANK) in the spectrometer and set it to zero absorbance
EX8-6 (of 12)

7. USING THE SPECTROMETER
Place a colored standard solution in the spectrometer
ABSORBANCE SPECTRUM – A graph of the absorbance of a solution at different wavelengths
If a solution appears blue, it is primarily absorbing its complimentary color, orange
EX8-7 (of 12)

8. USING THE SPECTROMETER
LAMBDA MAX (λmax) – The wavelength of maximum absorbance
Peak of the absorbance graph
When measuring the absorbance of solutions, it is most accurate to measure the absorbance at λmax
You will record the λmax in your Data Table
λmax
EX8-8 (of 12)

9. USING THE SPECTROMETER
Determine the absorbance of each standard solution at λmax
m (slope):
b (Y-intercept): 0.001
= mx + b
Correlation: 0.994
C: % % % % % A:
= mx + b
= ( %-1)C
This is called a CALIBRATION LINE
EX8-9 (of 12)

10. USING THE SPECTROMETER
Determine the percentage of CuSO4.5H2O in the sample if its absorbance is 0.246
m (slope):
b (Y-intercept): 0.001
= mx + b
Correlation: 0.994
y = mx b
= ( %-1)C
= ( %-1)C
= ( %-1)C
= C
_____________
%-1
0.255 % = C
= % CuSO4.5H2O %
= % KNO3
EX8-10 (of 12)

11. ɛ = extinction coefficient
AUGUST BEER
Proposed a mathematical explanation for the linear relationship between concentration and absorbance
A = mC + b
BEER’S LAW :
A = ɛ l C
+ 0
A = absorbance
ɛ = extinction coefficient
(a constant for a given solute at a given λ)
l = width of the cuvet holding the sample
(for our cuvets it is 1.00 cm)
C = concentration
(in our lab it’s in “% CuSO4.5H2O”)
l = 1.00 cm
EX8-11 (of 12)

12. Calculate the extinction coefficient for absorbance at a wavelength of 620 nm and using a 1.00 cm cuvet given the calibration line:
= ( %-1)C –
= mC + b
= ɛ l C + b
slope = ɛ l
m = ɛ
___ l
= %-1
_____________
1.00 cm
= %-1cm-1
EX8-12 (of 12)