smoking in lab: some chemistry behind it nature’s kitchen for some really interesting chemicals
TRANSCRIPT
Smoking in Lab: Some Chemistry Behind It
Nature’s kitchen for some really interesting chemicals
What is NOx?• NOx stands for the combination of NO and NO2.
• In smoke, NO is the original product of combustion of nitrogenous compounds.
• The NO is oxidized to NO2 within a few minutes in the presence of O2.
NO2
NO +(brown gas seen in smog)
[Shooter, 1993]
oxidants
Reaction Mechanism
NO2 + OH2 HNO2
CH3COOH
NH2
O2S
NH2
NH2
O2S
N
N+
sulfanilamide diazonium salt
NO2 -,
[Shooter, 1993]
CH3COOH
Reaction Mechanism
NH2
O2S
N
N+
+
NH3+
NH2+
Cl-
2
NH3+
NH2+
NH2
O2S
NN
Cl-
2
Azo Dye
diazonium salt
NEDA
[Shooter, 1993]
So what does this mean?• The amount of NO2 is related to the intensity of
the dye.
• More NO2 …
• …means more dye molecules…
• …means more intense color of solution.
• Now you can use a spectrophotometer to analyze the solution and see how color intensity relates to percentage transmittance or absorbance.
The Apparatus
¼ inch tubing Filter Disc
Cigarette 5/16 inch 60 ml Syringe
tubing • When assembling:
– Secure tubing to disk with copper wire– Note that cigarettes are fragile
Procedure Notes
• Allow cigarette to burn 10 seconds IN A HOOD
• When drawing up the smoke:– 35 mL in 2 seconds—THIS IS IMPORTANT!
• Draw up three 35 mL aliquots, in 1 minute intervals, to passivate the syringe
Procedure Notes• Then draw up 25 mL of indicator solution into
the syringe followed by an additional 35 mL smoke with the syringe held vertically (cigarette on top)
• Cap and shake VIGOROUSLY
• Allow the solution to develop 30 minutes– Shake occasionally
Procedure Notes• After 30 minutes expel the smoke and draw up
an additional 25 mL of indicator solution
• Measure the absorbance spectrum of the dye. Determine A at 550 nm.– Use absorbance mode, rather than %T– Ensure you have calibrated the SpectroVis– Use indicator solution as the blank
Notes on the Indicator• Take only the required amount
• RE-CAP THE BOTTLE!
• Store your sample of the solution in a Parafilm covered beaker outside the hood where your cigarettes are used.
Preparation of the Standards• Since the NOx is converted to nitrite during this
process, known concentrations of standard solutions can be made from potassium nitrite.
• These are used to create a calibration line
Beer’s Law
A=abc• A = Absorbance• a = absorptivity (units: often M-1cm-1)
– but can have different concentration units
• b = optical pathlength• c = concentration• A linear formula – a series of A’s at different c’s
should yield a straight line
Prepare Standard Solutions
• Stock Solution
• C1V1=C2V2
• Need a minimum of 3 standards but 4 or 5 are better
Beer’s Law Plot
• Acquire all of the A vs. c data
• Plot A vs. c
• Determine the best-fit line and the equation of the line
• From A of the solution from the cigarette, determine c of NOx using Beer’s Law Plot
Beer’s Law Plot: Example Data
Concentration
(M) A
1.2 x 10-5 0.292
9.0 x 10-6 0.194
6.0 x 10-6 0.144
3.0 x 10-6 0.086
0.00 0.000*
*Set when instrument calibrated
Beer’s Law Plot
A = 23.083 mM-1cm-1·l·c + 0.00476
Note the concentration scale
Analysis of Unknown Solution
Example: Unknown solution has a absorbance of 0.163 absorbance units. What is the dye concentration in the unknown?
Use the graph or equation of the line to get concentration:
Beer’s Law Plot
0.0069 mM
0.163
Beer’s Law Plot• Using the equation of the line (assuming the
same 1 cm cuvette):
c-1 -10.163 = 28.083 mM cm ×1cm× +0.00476
c-1 -1
0.163 -0.00476= = 0.0069 mM
28.083 mM cm ×1 cmc
-1 -1
0.163 -0.00476=
28.083 mM cm ×1 cm
For Today’s Lab• Standard solution preps are given
– You must calculate ACTUAL concentrations from your volume data
– Concentration will be in g/mL, not molarity
• Blank should be unexposed indicator solution
• Final value of NO2 should be reported in ppm
• You will need this website for post-lab question 1:http://www.arb.ca.gov/Aqd/almanac/almanac.htm