Lab 3A – Spectrophotometry and Beer’s Law

1) What is a spectrophotometer? (1 pt)

2) How does a spectrophotometer work? (1 pt)

3) As a beam of light goes through a sample, how is the amount of light absorbed determined? (1 pt)

4) When we say light is absorbed, what exactly in the sample absorbs the light? (1 pt)

5) What is lambda-max (λmax)? (1 pt)

6) Why is it important to measure samples at lambda-max (λmax)? (1 pt)

7) Why is a “blank” needed to calibrate the spectrophotometer? (1 pt)

8) What is the benefit to plotting the absorbance vs concentration? (1 pt)

9) What equation uses absorbance to calculate concentration? (1 pt)

10) After plotting a Beer’s Law plot (absorbance (y-axis) vs concentration (x-axis)), what factor on the best-fit line can be used to determine concentration if the absorbance is known? (1 pt)

Lab 3A – Spectrophotometry and Beer’s Law Answer

1. A spectrophotometer is a device employed to measure the amount of light that a sample absorbs.
2. The spectrophotometer worked by passing a beam of light through a sample and measuring the intensity of light reaching a detector.
3. The amount of monochromatic light absorbed by a sample is determined by comparing the intensities of the incident light (I0) and transmitted light (I1). The ratio of the intensity of the transmitted light (I1) to the intensity if the incident light (I0) is called transmittance (T) .