Question

6. a.) Explain the difference between transmittance, absorbance, and molar absorptivity. Which one is proportional to concentration?

6. b.) What is gained by analyzing a larger number of replicates of a sample? What are the practical limitations on minimizing the standard deviation?

6. c.) What are the necessary properties of the sample holder in spectroscopy? What type of cell can be used in the visible range? What type of sample cell should be used in the ultra-violet region of the spectrum?

Answer 1

a) Transmittance is the amount of light that can pass through a solution without getting absorbed. Absorbance is the amount of light that gets absorbed by the solution. If all the light is transmitted, absorbance is zero. If all light is absorbed, transmittance is zero.

The absorbance is proportional to concentration since it determines how much light will be absorbed.

b) Large sample size: a) gives better average data; b) Reduces error; c) This reduces the margin of error , that is the standard deviation

To minimise the standard deviation,

More accurate data and more samples are required which practically need more human, equipment and time resources.

c) Necessary properties:

• The cell holding the sample should be transparent to the wavelength region to be recorded.
• It should be cheap
• It should have desired transmittance characteristics of desired wavelength

Visible: Quartz or fused silica cuvettes are required for spectroscopy in the UV region.

UV: Quartz or fused silica cuvettes are required for spectroscopy in the UV region.