Quiz about Infrared Spectroscopy
Quiz about Infrared Spectroscopy

Infrared Spectroscopy Trivia Quiz


Infrared (IR) spectroscopy is used to determine the functional groups present in chemical compounds. The vibrations of different chemical bonds will absorb energy at different frequencies.

A multiple-choice quiz by Matthew_07. Estimated time: 5 mins.
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Author
Matthew_07
Time
5 mins
Type
Multiple Choice
Quiz #
295,974
Updated
Dec 03 21
# Qns
10
Difficulty
Average
Avg Score
6 / 10
Plays
1422
Last 3 plays: Guest 139 (8/10), Guest 131 (3/10), Guest 196 (6/10).
This quiz has 2 formats: you can play it as a or as shown below.
Scroll down to the bottom for the answer key.
1. As suggested by its name, an infrared spectrometer uses infrared electromagnetic radiation in its machine. This infrared radiation will result in which molecular activity? Hint

Molecular ionization
Molecular rotation
Molecular vibration
Molecular movement

2. One of the unit of measurement used for the wavelength of molecular absorption is micrometers. Its symbol is the Greek letter lambda. A more common unit is measured in cm^-1, which is defined as the number of complete loops in 1 cm. Its symbol is nu bar. What is this unit called? Hint

Frequency number
Hertz number
Wave number
Loop number

3. Bond stretching frequencies depend on two major factors, namely atomic weight and bond stiffness. The frequency absorbed is directly proportional to the bond strength (stiffness) but inversely proportional to the atomic weight. Which of the following bonds will give the highest absorption frequency value? Hint

C double bond C
C triple bond C
C single bond C
All of these will give the same frequency.

4. Depending on the location of the triple bond, the alkyne (C triple bond C) functional group gives different values of bond stretching frequency. Which type of alkyne will give higher frequency value? Terminal alkyne or internal alkyne?

Answer: (Terminal or internal)
5. A conjugated C double bond C (for example, 1,3-cyclohexadiene) will give lower absorption frequency value compared to that of an isolated C double bond C (for example, 1,4-cyclohexadiene).

True
False

6. A bond with more s character will absorb at higher absorption frequency since the s orbitals are closer to the nucleus of an atom compared to the p orbitals. Which of the following C-H bonds will give the highest absorption frequency? Hint

The C-H bond in C triple bond C single bond H
The C-H bond in C single bond C single bond H
The C-H bond in C double bond C single bond H
All of these will give the same absorption frequency

7. Will the -O-H functional group of both alcohols and carboxylic acids show the same absorption frequency?

Yes
No

8. Which of the following compounds will show two spikes at the -N-H stretching? Hint

All of these
A secondary amine
A primary amine
A tertiary amine

9. A typical infrared (IR) spectrum is divided into 2 parts, namely the left part with the absorption peaks at 1400 -4000 cm^-1 and the right part with the absorption peaks at 600 - 1400cm^-1. Beginners in this field only study the left part. The right part is studied by expert spectroscopists. What is the name given to this right part? Hint

Fingerprint region
Unsymmetrical region
Complex splitting region
Stretching region

10. A C double bond O bond absorbs at 1710 cm^-1. It may indicate an aldehyde, a ketone, or a carboxylic acid. You are told that an unknown chemical compound contains only three elements, namely C, H and O. You run an IR test and notice that the IR spectrum does not show any peak at the 1710 cm^-1 region. This IR spectrum suggests that the compound will most probably be a (an) ___. Hint

Ether
Nitrile
Ester
Sulfide


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Quiz Answer Key and Fun Facts
1. As suggested by its name, an infrared spectrometer uses infrared electromagnetic radiation in its machine. This infrared radiation will result in which molecular activity?

Answer: Molecular vibration

The infrared radiation in an infrared spectrometer will result in molecular vibration because it is a low-energy radiation (the radiation with the greatest energy is gamma rays while the lowest is radio waves).

On the other hand, X-rays will result in molecular ionization. This is the fundamental principle that is used in mass spectrometer machines.

Molecular vibration needs the least energy, followed by molecular rotation and movement (transition). Molecular ionization requires the most energy.
2. One of the unit of measurement used for the wavelength of molecular absorption is micrometers. Its symbol is the Greek letter lambda. A more common unit is measured in cm^-1, which is defined as the number of complete loops in 1 cm. Its symbol is nu bar. What is this unit called?

Answer: Wave number

If a wavelength is measured in micrometers, the value obtained is very small and it is very inconvenient to read and interpret the datum. Therefore, scientists have come out with another type of measurement, namely the wave number, which is measured in cm^-1.

For comparison, let's look at an example. 2.5 micrometer = 4000 cm^-1. The wavelength is 2.5 micrometer, or 0.0000025 meter, which is equivalent to 4000 cm^-1, which implies there are 400 complete loops in 1 cm.
3. Bond stretching frequencies depend on two major factors, namely atomic weight and bond stiffness. The frequency absorbed is directly proportional to the bond strength (stiffness) but inversely proportional to the atomic weight. Which of the following bonds will give the highest absorption frequency value?

Answer: C triple bond C

A C triple bond C is stronger than a C double bond C, which is stronger than a C single C bond. Therefore, the C triple C bond will give the highest bond stretching frequency.
4. Depending on the location of the triple bond, the alkyne (C triple bond C) functional group gives different values of bond stretching frequency. Which type of alkyne will give higher frequency value? Terminal alkyne or internal alkyne?

Answer: Terminal

Terminal alkynes are IR active (have dipole moment) while internal alkynes may be IR inactive (do not have dipole moment since the molecules are symmetrically substituted).
5. A conjugated C double bond C (for example, 1,3-cyclohexadiene) will give lower absorption frequency value compared to that of an isolated C double bond C (for example, 1,4-cyclohexadiene).

Answer: True

Conjugation will result in the decrease of absorption frequency. For comparison, an isolated C double bond C absorbs at 1640 - 1680 cm^-1. A conjugated C double bond absorbs at 1620 - 1640 cm^-1 while an aromatic C double bond C absorbs at 1600 cm^-1.

This is because conjugation will result in the delocalization of electrons (electrons do not "stay" in just one place but they are resonated between two bonds).
6. A bond with more s character will absorb at higher absorption frequency since the s orbitals are closer to the nucleus of an atom compared to the p orbitals. Which of the following C-H bonds will give the highest absorption frequency?

Answer: The C-H bond in C triple bond C single bond H

The C-H bond in C triple bond C single bond H is sp hybridized, which means the bond has 1/2 s character. On the other hand, the C-H bond in C double bond C single bond H (sp2 hybridized) and the C-H bond in C single bond C single bond H (sp3 hybridized) have 1/3 and 1/4 s character respectively.
7. Will the -O-H functional group of both alcohols and carboxylic acids show the same absorption frequency?

Answer: No

The alcohol -O-H functional group will show absorption peak at 3300 cm^-1 while the carboxylic acid -O-H group will show its peak at 3000cm^-1.
8. Which of the following compounds will show two spikes at the -N-H stretching?

Answer: A primary amine

A primary amine's general formula is R-NH2. The two spikes come from the two hydrogen atoms attached to the N atom. A secondary amine's general formula is R2-NH. Only one spike will be shown at the -N-H stretching. On the other hand, the general formula for a tertiary amine is R3N. No hydrogen atom is attached to the N atom, so no spike will be shown.
9. A typical infrared (IR) spectrum is divided into 2 parts, namely the left part with the absorption peaks at 1400 -4000 cm^-1 and the right part with the absorption peaks at 600 - 1400cm^-1. Beginners in this field only study the left part. The right part is studied by expert spectroscopists. What is the name given to this right part?

Answer: Fingerprint region

The fingerprint region shows very complex patterns caused by symmetrical stretching, unsymmetrical stretching, scissoring, rocking, bending, wagging and twisting of the molecules' chemical bonds.
10. A C double bond O bond absorbs at 1710 cm^-1. It may indicate an aldehyde, a ketone, or a carboxylic acid. You are told that an unknown chemical compound contains only three elements, namely C, H and O. You run an IR test and notice that the IR spectrum does not show any peak at the 1710 cm^-1 region. This IR spectrum suggests that the compound will most probably be a (an) ___.

Answer: Ether

A compound with nitrile functional group (C triple bond N) contains nitrogen, N. On the other hand, a compound with sulfide functional group (C single bond S single bond C) contains sulfide, S. The functional group of ether is C single bond O single bond C which usually absorbs at 1200 cm^-1.

The functional group of esther contains C double bond O as part of its structure so it will absorb around 1710 cm^-1, too.
Source: Author Matthew_07

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This quiz is part of series Matthew's Chemistry Quizzes:

A collection of my chemistry quizzes encompassing the disciplines of organic and analytical chemistry. This list covers topics on elements, chemical functional groups, and specialized analytical techniques.

  1. Hydrogen - The Lightest Element Average
  2. Helium - The Balloon Gas Average
  3. Gold, Silver and Bronze Average
  4. Matter and Substance Average
  5. Elementary Scientists and Mathematicians Average
  6. Ethers and Epoxides Tough
  7. Analytical Chemistry Tough
  8. Infrared Spectroscopy Average
  9. Mass Spectrometry Average

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