1. Smoking in Lab: Some Chemistry Behind It Nature’s kitchen for some really interesting chemicals

2. Before We Get Started

3. What is NO x ? NO x stands for the combination of NO and NO 2. In smoke, NO is the original product of combustion of nitrogenous compounds. The NO is oxidized to NO 2 within a few minutes in the presence of O 2.

4. Reaction Mechanism

6. So what does this mean? The amount of NO 2 is related to the intensity of the dye. More NO 2 … …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.

7. 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

8. 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

9. 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

10. 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

11. 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.

12. 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

13. Beer’s Law A=abc A = Absorbance a = absorptivity (units: often M -1 cm -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

14. Prepare Standard Solutions Stock Solution C 1 V 1 =C 2 V 2 Need a minimum of 3 standards but 4 or 5 are better

15. 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

16. 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 0.000.000 * * Set when instrument calibrated

17. Beer’s Law Plot A = 23.083 mM -1 cm -1 · l ·c + 0.00476 Note the concentration scale

18. 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:

19. Beer’s Law Plot 0.0069 mM 0.163

20. Beer’s Law Plot Using the equation of the line (assuming the same 1 cm cuvette):

21. 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 NO 2 should be reported in ppm You will need this website for post-lab question 1: http://www.arb.ca.gov/Aqd/almanac/almanac.htm