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This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License   Lab...
This session…. <ul><li>Overview of the practical… </li></ul><ul><li>Statistical analysis…. </li></ul><ul><li>Take a look a...
The Practical <ul><li>Determine the thiocyanate (SCN - ) in a sample of your saliva using a colourimetric method of analys...
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License   Typ...
Beer-Lambert Law <ul><ul><li>Beers Law states that  absorbance is proportional to concentration  over a certain concentrat...
Beer-Lambert Law <ul><li>Beer’s law is valid at low concentrations, but breaks down at higher concentrations </li></ul><ul...
Beer-Lambert Law <ul><li>If your unknown has a higher concentration than your highest standard, you have to ASSUME that li...
Quantitative Analysis <ul><li>A < 1 </li></ul><ul><ul><li>If A > 1: </li></ul></ul><ul><ul><ul><li>Dilute the sample </li>...
Quantitative Analysis This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England...
Statistical Analysis This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England ...
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License   Mea...
Normal Distribution This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England &...
Mean and Standard Deviation This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: E...
Standard Deviation <ul><li>Measures the variation of the samples: </li></ul><ul><ul><li>Population std (  ) </li></ul></u...
   or s? <ul><li>In forensic analysis, the rule of thumb is: </li></ul><ul><ul><li>If n > 15 use   </li></ul></ul><ul><u...
Absolute Error and Error % <ul><li>Absolute Error </li></ul><ul><ul><li>Experimental value – True Value </li></ul></ul><ul...
Confidence limits This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & W...
Control Data <ul><li>Work out the mean and standard deviation of the control data </li></ul><ul><ul><li>Use only 1 value p...
Control Data <ul><li>Calculate the Absolute Error and the Error % </li></ul><ul><ul><li>True value of [SCN – ] in the cont...
Control Data <ul><li>Plot a Control Chart for the control data </li></ul>This work is licensed under a Creative Commons At...
Significance <ul><li>Divide the data into six groups: </li></ul><ul><ul><li>Smokers </li></ul></ul><ul><ul><li>Non-smokers...
Significance <ul><li>Plot the values on a bar chart </li></ul><ul><li>Add error bars (y-axis)  </li></ul><ul><ul><li>at th...
Significance This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales ...
Identifying Significance <ul><li>In the most simplistic terms: </li></ul><ul><ul><li>If there is no overlap of error bars ...
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License   Ack...
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Chemical and Physical Properties: Practical Session

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Lecture materials for the Introductory Chemistry course for Forensic Scientists, University of Lincoln, UK. See http://forensicchemistry.lincoln.ac.uk/ for more details.

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Transcript of "Chemical and Physical Properties: Practical Session"

  1. 1. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Lab 6: Saliva Practical Beer-Lambert Law University of Lincoln presentation
  2. 2. This session…. <ul><li>Overview of the practical… </li></ul><ul><li>Statistical analysis…. </li></ul><ul><li>Take a look at an example control chart… </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  3. 3. The Practical <ul><li>Determine the thiocyanate (SCN - ) in a sample of your saliva using a colourimetric method of analysis </li></ul><ul><li>Calibration curve to determine the [SCN - ] of the unknowns </li></ul><ul><li>This was ALL completed in the practical class </li></ul><ul><li>Some of your absorbance values may have been higher than the absorbance values of your top standards… is this a problem???? </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  4. 4. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Types of data QUALITATIVE Non numerical i.e what is present? QUANTITATIVE Numerical: i.e. How much is present?
  5. 5. Beer-Lambert Law <ul><ul><li>Beers Law states that absorbance is proportional to concentration over a certain concentration range </li></ul></ul><ul><ul><li>A =  cl </li></ul></ul><ul><ul><li>A = absorbance </li></ul></ul><ul><ul><li> = molar extinction coefficient (M -1 cm -1 or mol -1 L cm -1 ) </li></ul></ul><ul><ul><li>c = concentration (M or mol L -1 ) </li></ul></ul><ul><ul><li>l = path length (cm) (width of cuvette) </li></ul></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  6. 6. Beer-Lambert Law <ul><li>Beer’s law is valid at low concentrations, but breaks down at higher concentrations </li></ul><ul><li>For linearity, A < 1 </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License 1
  7. 7. Beer-Lambert Law <ul><li>If your unknown has a higher concentration than your highest standard, you have to ASSUME that linearity still holds ( NOT GOOD for quantitative analysis) </li></ul><ul><li>Unknowns should ideally fall within the standard range </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License 1
  8. 8. Quantitative Analysis <ul><li>A < 1 </li></ul><ul><ul><li>If A > 1: </li></ul></ul><ul><ul><ul><li>Dilute the sample </li></ul></ul></ul><ul><ul><ul><li>Use a narrower cuvette </li></ul></ul></ul><ul><ul><ul><ul><li>(cuvettes are usually 1 mm, 1 cm or 10 cm) </li></ul></ul></ul></ul><ul><li>Plot the data (A v C) to produce a calibration ‘curve’ </li></ul><ul><li>Obtain equation of straight line (y=mx) from line of ‘best fit’ </li></ul><ul><li>Use equation to calculate the concentration of the unknown(s) </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  9. 9. Quantitative Analysis This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  10. 10. Statistical Analysis This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  11. 11. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Mean The mean provides us with a typical value which is representative of a distribution
  12. 12. Normal Distribution This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  13. 13. Mean and Standard Deviation This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License MEAN
  14. 14. Standard Deviation <ul><li>Measures the variation of the samples: </li></ul><ul><ul><li>Population std (  ) </li></ul></ul><ul><ul><li>Sample std (s) </li></ul></ul><ul><li> = √(  (x i – µ ) 2 /n) </li></ul><ul><li>s =√(  (x i – µ ) 2 /(n-1)) </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  15. 15.  or s? <ul><li>In forensic analysis, the rule of thumb is: </li></ul><ul><ul><li>If n > 15 use  </li></ul></ul><ul><ul><li>If n < 15 use s </li></ul></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  16. 16. Absolute Error and Error % <ul><li>Absolute Error </li></ul><ul><ul><li>Experimental value – True Value </li></ul></ul><ul><li>Error % </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  17. 17. Confidence limits This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License 1  = 68% 2  = 95% 2.5  = 98% 3  = 99.7%
  18. 18. Control Data <ul><li>Work out the mean and standard deviation of the control data </li></ul><ul><ul><li>Use only 1 value per group </li></ul></ul><ul><ul><ul><li>Which std is it?  or s? </li></ul></ul></ul><ul><li>This will tell us how precise your work is in the lab </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  19. 19. Control Data <ul><li>Calculate the Absolute Error and the Error % </li></ul><ul><ul><li>True value of [SCN – ] in the control = 2.0 x 10 –3 M </li></ul></ul><ul><li>This will tell us how accurately you work, and hence how good your calibration is!!! </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  20. 20. Control Data <ul><li>Plot a Control Chart for the control data </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License 2.5  2 
  21. 21. Significance <ul><li>Divide the data into six groups: </li></ul><ul><ul><li>Smokers </li></ul></ul><ul><ul><li>Non-smokers </li></ul></ul><ul><ul><li>Male </li></ul></ul><ul><ul><li>Female </li></ul></ul><ul><ul><li>Meat-eaters </li></ul></ul><ul><ul><li>Rabbits </li></ul></ul><ul><li>Work out the mean and std for each group (  or s?) </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  22. 22. Significance <ul><li>Plot the values on a bar chart </li></ul><ul><li>Add error bars (y-axis) </li></ul><ul><ul><li>at the 95% confidence limit – 2.0  </li></ul></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  23. 23. Significance This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  24. 24. Identifying Significance <ul><li>In the most simplistic terms: </li></ul><ul><ul><li>If there is no overlap of error bars between two groups, you can be fairly sure the difference in means is significant </li></ul></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  25. 25. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Acknowledgements <ul><li>JISC </li></ul><ul><li>HEA </li></ul><ul><li>Centre for Educational Research and Development </li></ul><ul><li>School of natural and applied sciences </li></ul><ul><li>School of Journalism </li></ul><ul><li>SirenFM </li></ul><ul><li>http://tango.freedesktop.org </li></ul>
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