Spectrophotometry: Principles, Applications, and Practice

Question 1

Which component is NOT typically found in a spectrophotometer?

Accepted Answer

Mass spectrometer

Answer

Light source

Answer

Sample holder

Answer

Detector

Question 2

Which unit is used to express the absorbance of a solution?

Accepted Answer

Absorbance units (AU)

Answer

Molarity

Answer

Percentage

Answer

Transmittance

Question 3

In spectrophotometry, why is a reference cell crucial, and how does it enhance measurement accuracy?

Accepted Answer

A reference cell corrects for background noise and sample impurities, allowing for precise analyte concentration determination.

Answer

A reference cell contains the same solution as the sample, eliminating the need for background noise correction.

Answer

A reference cell adjusts the spectrophotometer's wavelength setting, ensuring optimal light absorption.

Answer

Reference cells are not essential in spectrophotometry as they do not significantly impact measurement accuracy.

Question 4

What is the fundamental principle of spectrophotometry?

Accepted Answer

Molecules' absorption of electromagnetic radiation

Answer

Molecules' emission of electromagnetic radiation

Answer

Molecules' reflection of electromagnetic radiation

Answer

Molecules' transmission of electromagnetic radiation

Question 5

What is the primary purpose of using a calibration curve in spectrophotometry?

Accepted Answer

Determining the concentration of an unknown sample

Answer

Identifying the analyte in a sample

Answer

Validating the spectrophotometer's accuracy

Answer

Measuring the absorbance of a reference standard

Question 6

Which type of spectrophotometer utilizes a prism to disperse light?

Accepted Answer

UV-Vis spectrophotometer

Answer

Fluorometer

Answer

Atomic absorption spectrophotometer

Answer

FTIR spectrophotometer

Question 7

What is the main purpose of utilizing a reference cell in spectrophotometric measurements?

Accepted Answer

Correcting for background absorbance

Answer

Calibrating the spectrophotometer

Answer

Containing the sample solution

Answer

Adjusting the light intensity

Question 8

Identify the component that is NOT part of a spectrophotometer.

Accepted Answer

Chromatographic column

Answer

Light source

Answer

Sample holder

Answer

Detector

Question 9

According to the Beer-Lambert law, what is the relationship between absorbance and concentration?

Accepted Answer

Absorbance is directly proportional to concentration.

Answer

Absorbance is inversely proportional to concentration.

Answer

Absorbance is proportional to the square of concentration.

Answer

There is no relationship between absorbance and concentration.

Question 10

In spectrophotometry, what is the purpose of using a monochromatic light source?

Accepted Answer

To ensure specific wavelength absorption by the sample.

Answer

To enhance the intensity of the light beam.

Answer

To reduce background interference.

Answer

To calibrate the instrument.

Question 11

How can spectrophotometry determine the unknown concentration of a sample?

Accepted Answer

Plot a calibration curve of absorbance versus concentration and extrapolate the unknown concentration.

Answer

Use the Beer-Lambert law to directly calculate the concentration.

Answer

Compare the absorbance of the unknown sample to a known standard.

Answer

Measure the absorbance of the unknown sample at multiple wavelengths.

Question 12

Which type of molecule typically absorbs strongly in the visible or UV region of the electromagnetic spectrum?

Accepted Answer

Molecules with conjugated double bonds

Answer

Ions

Answer

Saturated hydrocarbons

Answer

Water

Question 13

What is the common unit of absorbance measurement?

Accepted Answer

Absorbance units (AU)

Answer

Molar absorptivity

Answer

Percent transmittance

Answer

Concentration (M)

Question 14

In spectrophotometry, the primary purpose of a blank solution is to:

Accepted Answer

Cancel out solvent absorbance

Answer

Calibrate the instrument

Answer

Determine analyte concentration

Answer

Prevent sample contamination

Question 15

What differentiates absorbance from transmittance?

Accepted Answer

Absorbance measures absorbed light, while transmittance measures transmitted light.

Answer

Absorbance measures transmitted light, while transmittance measures absorbed light.

Answer

Absorbance and transmittance represent identical measurements.

Answer

Absorbance measures light intensity, while transmittance measures light wavelength.

Question 16

Within a spectrophotometer setup, what is the primary function of a cuvette?

Accepted Answer

To hold the sample

Answer

To focus the light beam

Answer

To calibrate the instrument

Answer

To convert light into an electrical signal

Question 17

Which of the following is not a fundamental component of a spectrophotometer?

Accepted Answer

Printer

Answer

Light source

Answer

Sample compartment

Answer

Detector

Question 18

According to the Beer-Lambert law, absorbance is directly proportional to:

Accepted Answer

Both concentration and path length

Answer

Concentration of the analyte only

Answer

Path length of the light beam only

Answer

Neither concentration nor path length

Question 19

Calibration of a spectrophotometer is typically performed using:

Accepted Answer

A standard solution

Answer

A blank solution

Answer

A sample solution

Answer

A reference solution

Question 20

In spectrophotometry, the most commonly employed wavelength range is:

Accepted Answer

Visible

Answer

Ultraviolet

Answer

Infrared

Answer

Microwave

Question 21

When working with spectrophotometers and hazardous chemicals, which safety precautions should you prioritize?

Accepted Answer

Wear appropriate personal protective equipment (gloves, safety glasses, lab coat).

Answer

Handle chemicals directly with bare hands.

Answer

Look directly into the spectrophotometer's light source.

Answer

Use mouth pipetting for transferring solutions.

Question 22

What is the main advantage of double-beam spectrophotometers over single-beam spectrophotometers?

Accepted Answer

Higher accuracy due to compensation for light source fluctuations

Answer

Increased sensitivity for detecting low concentrations

Answer

Greater versatility for a wider range of measurements

Answer

Equal accuracy and precision in both types

Question 23

Which of the following is NOT a component of a spectrophotometer?

Accepted Answer

Burette

Answer

Cuvette

Answer

Detector

Answer

Light source

Question 24

The Beer-Lambert law states that the absorbance of a solution is directly proportional to:

Accepted Answer

Concentration and path length

Answer

Temperature and concentration

Answer

Concentration only

Answer

Path length only

Question 25

What type of radiation is used in spectrophotometry?

Accepted Answer

Electromagnetic

Answer

Ionizing

Answer

Mechanical

Answer

Acoustic

Question 26

What is the purpose of a monochromator in a spectrophotometer?

Accepted Answer

To isolate light of a specific wavelength

Answer

To amplify the light signal

Answer

To convert light to an electrical signal

Question 27

What is the typical wavelength range used in spectrophotometry?

Accepted Answer

190-1100 nm

Answer

100-500 nm

Answer

1100-2500 nm

Answer

500-1000 nm

Question 28

Which of the following factors can affect the absorbance of a solution?

Accepted Answer

Concentration, path length, temperature, and solvent

Answer

Temperature and solvent only

Answer

Concentration and path length only

Question 29

What is the SI unit of absorbance?

Accepted Answer

Absorbance unit (AU)

Answer

Mole per liter (M)

Answer

Centimeters (cm)

Answer

Millimoles per liter (mM)

Question 30

Which of the following is a limitation of spectrophotometry?

Accepted Answer

Can be affected by interferences

Answer

Provides highly accurate results

Answer

Can be used for all samples

Answer

Is a non-destructive technique

Question 31

Which of the following components is NOT found in a spectrophotometer?

Accepted Answer

Gas chromatography column

Answer

Light source

Answer

Detector

Answer

Sample cell

Question 32

According to the Beer-Lambert law, how does absorbance relate to concentration?

Accepted Answer

Absorbance is directly proportional to concentration.

Answer

Absorbance is squared proportional to concentration.

Answer

Absorbance is inversely proportional to concentration.

Question 33

What is the term used to describe the specific wavelength of light that a substance absorbs?

Accepted Answer

Absorption maximum

Answer

Extinction coefficient

Answer

Molar absorptivity

Question 34

Which method is used to determine the concentration of a substance using spectrophotometry?

Accepted Answer

Measuring the absorbance of a sample at a specific wavelength and applying the Beer-Lambert law.

Answer

Measuring the fluorescence of the sample.

Answer

Comparing the color of the sample to known standards.

Question 35

What is a calibration curve in spectrophotometry?

Accepted Answer

A graph plotting absorbance against concentration.

Answer

A graph plotting transmittance against concentration.

Answer

A graph plotting fluorescence against wavelength.

Answer

A graph plotting wavelength against absorbance.

Question 36

Which factors can potentially affect the accuracy of spectrophotometric measurements?

Accepted Answer

Sample preparation, instrument calibration, and environmental conditions.

Answer

Instrument calibration

Answer

Sample preparation

Question 37

What is the purpose of using a blank in spectrophotometry?

Accepted Answer

To set the spectrophotometer to zero and correct for background absorbance.

Answer

To calculate the concentration of the analyte

Answer

To calibrate the instrument

Question 38

How can spectrophotometry be used to identify a substance?

Accepted Answer

By comparing its absorption spectrum to a known reference spectrum.

Answer

By determining its molecular weight.

Answer

By measuring its refractive index.

Question 39

What is the distinction between absorbance and transmittance?

Accepted Answer

Absorbance measures the amount of light absorbed, while transmittance measures the amount of light transmitted.

Answer

Absorbance measures the intensity of light, while transmittance measures the wavelength of light.

Question 40

Which equation represents the Beer-Lambert Law?

Accepted Answer

A = εbc

Answer

A = ε/bc

Answer

A = b/εc

Answer

A = c/εb

Question 41

A solution containing a colored compound has a molar absorptivity (ε) of 5000 L mol⁻¹ cm⁻¹. If the absorbance is 0.8 and a cuvette with a path length of 1 cm is used, calculate the concentration of the compound in mol L⁻¹.

Accepted Answer

1.6 x 10⁻⁴

Answer

6.25 x 10³

Answer

4 x 10⁻³

Answer

1.25 x 10⁻⁴

Question 42

How is transmittance related to absorbance?

Accepted Answer

Absorbance is the negative logarithm of transmittance.

Answer

Transmittance is the negative logarithm of absorbance.

Answer

Absorbance and transmittance are directly proportional.

Question 43

During spectrophotometer calibration, what is the role of a blank solution?

Accepted Answer

To zero the absorbance of the solvent and cuvette.

Answer

To calculate the analyte's molar absorptivity.

Answer

To determine the analyte's wavelength of maximum absorption.

Question 44

Which component of a spectrophotometer separates white light into its individual wavelengths?

Accepted Answer

Monochromator

Answer

Detector

Answer

Cuvette

Answer

Light source

Question 45

In UV-Vis spectrophotometry, what type of electromagnetic radiation is utilized?

Accepted Answer

Ultraviolet and visible light

Answer

Infrared radiation

Answer

Radio waves

Answer

X-rays

Question 46

A blood sample analyzed for glucose concentration using a spectrophotometric method exhibits an absorbance exceeding the highest standard of the calibration curve. What is the appropriate action?

Accepted Answer

Dilute the sample and reanalyze.

Answer

Repeat the analysis using a different wavelength.

Answer

Report the absorbance value without adjustment.

Answer

Extrapolate the calibration curve to approximate the concentration.

Question 47

In spectrophotometry, what type of graph is commonly used to determine the unknown concentration of a sample?

Accepted Answer

Calibration curve

Answer

Histogram

Answer

Scatter plot

Answer

Lineweaver-Burk plot