Question 1

Which of the following best describes the relationship between absorbance ($$A) $$and transmittance ($$T) in a $$spectrophotometric analysis?

Accepted Answer

$$A = -\log_{10}(T)$$

Question 2

A student prepares a blank solution for use in a spectrophotometer. What is the primary purpose of this blank?

Accepted Answer

To calibrate the spectrophotometer by accounting for absorbance due to the solvent and cuvette

Question 3

Which region of the electromagnetic spectrum is used in visible spectrophotometry?

Accepted Answer

400 - 700 \ nm

Question 4

If a chlorophyll solution shows maximum absorbance at 660 nm and 440 nm, what color(s) of light does it absorb most strongly?

Accepted Answer

Red and blue

Question 5

Why does a green leaf appear green to the human eye?

Accepted Answer

It reflects green wavelengths and absorbs other colors

Question 6

Which step is essential before measuring the absorbance of a sample in a spectrophotometer?

Accepted Answer

Zeroing the machine with a blank solution

Question 7

A student measures the absorbance of a chlorophyll solution at several wavelengths and finds two peaks. What does this indicate about the pigment?

Accepted Answer

It absorbs light most efficiently at those two wavelengths

Question 8

Which of the following best explains why the rate of photosynthesis is highest under red and blue light?

Accepted Answer

Chlorophyll absorbs red and blue light most efficiently, providing energy for photosynthesis

Question 9

Which component of the spectrophotometer is responsible for selecting a specific wavelength of light?

Accepted Answer

Monochromator (prism or grating)

Question 10

If a solution has an absorbance of 1.0 at a certain wavelength, what percentage of the incident light is transmitted through the solution? (Use $$A = -\log_{10}(T)$$, where $$T is $$the fraction of light transmitted.)

Accepted Answer

10\%

Question 11

A student forgets to use a blank when measuring absorbance. What is the most likely consequence?

Accepted Answer

The absorbance readings will be artificially high due to the solvent and cuvette

Question 12

Which of the following is NOT a factor that affects the absorbance measured by a spectrophotometer?

Accepted Answer

The color of the cuvette cap

Question 13

If the path length of the cuvette is doubled, what happens to the absorbance, assuming concentration and wavelength remain constant? (Use Beer-Lambert Law: $$A = \varepsilon c l)$$

Accepted Answer

Absorbance doubles

Question 14

Which of the following best describes why ethanol is used in the extraction of chlorophyll from spinach leaves?

Accepted Answer

Ethanol dissolves chlorophyll, allowing it to be separated from the leaf tissue

Question 15

A solution transmits 25\% of the incident light at a certain wavelength. What is its absorbance? (Use $$A = -\log_{10}(T)$$, where $$T is $$the fraction transmitted.)

Accepted Answer

$$A = 0.60$$ \ (since \ T = 0.25, \ A = -\log_{10}(0.25) = 0.60)$

Question 16

Which of the following steps is performed immediately after filtering the spinach extract in the chlorophyll extraction procedure?

Accepted Answer

Centrifuge the solution to remove leaf residue

Question 17

Why is it important to wipe the outside of the cuvette before placing it in the spectrophotometer?

Accepted Answer

To prevent fingerprints or droplets from affecting the absorbance reading

Question 18

A student finds that the absorbance of a chlorophyll solution is highest at 440 nm and lowest at 520 nm. What can be inferred about the color of the solution?

Accepted Answer

The solution appears green because it transmits green light (around 520 nm)

Spectrophotometry of Chlorophyll Pigments: Principles and Laboratory Practice

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