Work through the list without notes. If you cannot do a statement, follow its link, then come back. Guide = study guide; Practice = practice questions.
Understanding
- I can state the Beer-Lambert law, A = εbc, and give the meaning and unit of each symbol. (Guide: “What the law says”)
- I can explain that ε depends on the species and the wavelength, but not on the concentration. (Guide: “Molar absorptivity and the choice of wavelength”; Practice Q3, Q4)
- I can explain why absorbance is proportional to both path length and concentration, using the number of absorbing particles in the light beam. (Guide: “Why b and c matter”; Practice Q2, Q7)
- I can explain why the instrument is set to λmax and zeroed with a blank. (Guide: Figures 1 and 2; Practice Q3, Q6)
Calculation
- I can rearrange A = εbc to find any one quantity, with units that cancel correctly. (Guide: Worked example 1; Practice Q1)
- I can find ε from the gradient of a calibration curve and read an unknown concentration from it. (Guide: Worked example 2; Practice Q5)
- I can multiply back by a dilution factor to find the concentration of the original sample. (Guide: Worked example 2; Practice Q6)
- I can predict a new absorbance when the path length or concentration changes. (Practice Q2, Q5)
Reasoning
- I can identify sources of error in an absorbance experiment, such as smudges, bubbles, cloudiness, water droplets or a different cuvette. (Guide: Worked example 3)
- I can predict whether an error makes the calculated concentration too high or too low, saying first what happens to A. (Practice Q4, Q6, Q7)
- I can explain why the unknown’s absorbance should lie within the range of the standards. (Guide: “Calibration curves”)
All ticked? Unit 3 is complete. Move on to Topic 4.1, Introduction for Reactions, or return to the course roadmap.