Teaching Points for Beer’s Law lab


  • they will need to make sure they pay attention to the ‘fold dilution’ in the figure because for the first two it is 10 -fold and then it is 2-fold thereafter
  • Make sure they understand how to use  C1V1= C2V2   and that V2 includes the extra water added.
  • If using Shackleton or Henry specs – they should be sure to follow the correct order for plugging in the power and USB cables. It is written on the spec. Spec should be unplugged when done.
  • Be sure they report their Maximal Wavelength in the notbeook and report. Many people missed it last year.
  • They should put a copy of the table and graph in their notebook and report.
  • They should initially graph all points. But then we should point out to them that maybe one or two of them do not fall on the same line as the other points. These points can then be manually deleted in Excel to make a straight curve.
  • Graph should have X and Y axis labels. No title (that can be saved for the caption). Error bars should be present. (Be sure you know how to do CUSTOM error bars in Excel) – if not, I can show you.
  • We will have to show them how to display the Equation of the best fit line for their graph. Then they will use the slope and y -intercept to calculate the unkown.
  • Be sure they understand Dimensional Analysis for determining the Units of the molar absorptivity using Beer’s Law. – the units have to cancel

ADDED 020711 – Monday

We have 2 borrowed laptops from UTeach. They should work fine.

WE HAVE 2 new SPECS also (named Thomas & William) – The new small, black specs need to have Logger Pro ver. 3.8.3   – I believe all the computers have this.

If they don’t have enough data points within the range of 0.005 – 1.5  – they may need to make more dilutions and measure some more.

Don’t let them write on the tubes or the cuvettes with permanent marker – they should use labeling tape.

Can use either round or square cuvettes – but be sure they know there is a difference in volume for them. (squares need more liquid) – (which is why we prefer the round ones for real experiments – to save on reagent costs)

Use the cheap, re-usable 15 ml tubes that are non-sterile – they are back in our cubby or on top of the bench by the yellow fire cabinet.

The protocol is up on Black Board – if you need a paper copy – I have some.

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