Sample Quizzes For Preparation: Analytical Techniques

A2 Level Chemistry – Quiz

Chapter 37: Analytical Techniques

Question 1: What is the role of the stationary phase in thin-layer chromatography (TLC)?

A. To dissolve the sample mixture
B. To allow compounds to travel quickly
C. To adsorb compounds for separation
D. To identify the Rf value

Question 2: Which of the following best describes the mobile phase in TLC?

A. An unreactive gas
B. A solid adsorbent
C. A solvent that carries the compounds up the plate
D. Aluminium oxide on a plate

Question 3: What is the correct formula for calculating the Rf value in TLC?

A. Rf = solvent front / distance moved by solute
B. Rf = distance moved by solvent / total height of plate
C. Rf = distance moved by solute / distance moved by solvent
D. Rf = baseline / solvent front

Question 4: Why might a substance have a low Rf value in TLC?

A. It has high solubility in the solvent
B. It is non-polar
C. It strongly interacts with the stationary phase
D. It evaporates quickly

Question 5: In gas chromatography, what is the mobile phase?

A. A non-polar solvent
B. An inert gas
C. A high-boiling liquid
D. Aluminium oxide

Question 6: What is meant by the term ‘retention time’ in gas chromatography?

A. Time taken to inject the sample
B. Time taken for a substance to leave the column
C. Time taken for the solvent to rise
D. Time for the baseline to appear

Question 7: In gas chromatography, which of the following would increase the retention time of a substance?

A. Low boiling point and weak interaction
B. Strong attraction to mobile phase
C. Strong interaction with stationary phase
D. Being injected quickly

Question 8: What is the stationary phase in gas chromatography typically made of?

A. Non-volatile solid
B. Non-polar liquid on a solid support
C. Inert gas
D. Ethanol

Question 9: What does each peak in a gas chromatogram represent?

A. An impurity
B. A calibration error
C. A different compound in the mixture
D. Solvent concentration

Question 10: Which of the following is not a factor affecting retention time in GC?

A. Boiling point
B. Temperature of the column
C. Colour of the compound
D. Interaction with stationary phase

Question 11: What does a carbon-13 NMR spectrum detect?

A. All carbon atoms in a compound
B. Carbon atoms in unique environments
C. Carbon atoms with odd mass number
D. Hydrogen atoms

Question 12: How many signals would be observed in a ¹³C NMR spectrum of methane (CH₄)?

A. 1
B. 2
C. 3
D. 4

Question 13: In ¹³C NMR, which carbon type would appear around 200 ppm?

A. Alkene carbon
B. Aromatic carbon
C. Alkane carbon
D. Carbonyl carbon

Question 14: Why do ¹³C NMR spectra usually not show splitting?

A. Carbon atoms do not absorb radiation
B. ¹³C atoms do not couple with other ¹³C atoms
C. Carbon atoms are not magnetic
D. Chemical shifts are identical

Question 15: In ¹³C NMR, what determines the number of peaks?

A. The number of protons
B. Number of unique carbon environments
C. Amount of sample
D. Bond strength

Question 16: Which of the following solvents is used in ¹H NMR to avoid interference from hydrogen?

A. Ethanol
B. Water
C. CDCl₃
D. D₂O

Question 17: What is the role of tetramethylsilane (TMS) in ¹H NMR?

A. Solubilises the sample
B. Reference for chemical shift
C. Removes impurities
D. Reacts with OH groups

Question 18: What does the ‘n + 1’ rule represent in ¹H NMR splitting?

A. Number of hydrogen atoms in molecule
B. Number of bonds in a molecule
C. Number of peaks based on neighbouring protons
D. Number of carbon atoms

Question 19: Which of the following is a triplet in ¹H NMR?

A. 0 neighbours
B. 1 neighbour
C. 2 neighbours
D. 3 neighbours

Question 20: What information does the area under each peak in ¹H NMR provide?

A. Mass of sample
B. Number of equivalent hydrogen atoms
C. Number of carbon atoms
D. Type of solvent used

Question 21: Which type of proton would appear furthest downfield (highest ppm) in ¹H NMR?

A. CH₃ group
B. Alkene proton
C. Aldehyde proton
D. Aromatic proton

Question 22: What causes spin-spin splitting in ¹H NMR spectra?

A. Electron-electron interaction
B. Adjacent protons influencing magnetic environment
C. Sample concentration
D. Magnetic field strength

Question 23: What does it indicate if a signal disappears after adding D₂O in ¹H NMR?

A. Water contamination
B. Proton exchange occurred with O–H or N–H
C. Impurity removal
D. Instrument error

Question 24: In a ¹H NMR spectrum, how would a CH₃ group next to CH₂ appear?

A. Singlet
B. Doublet
C. Triplet
D. Quartet

Question 25: What is a singlet in ¹H NMR?

A. One hydrogen with no neighbouring protons
B. A hydrogen on a benzene ring
C. A CH group with 2 neighbours
D. Proton next to O atom

Question 26: What type of peak would a carboxylic acid proton typically produce in ¹H NMR?

A. Broad singlet around 11–12 ppm
B. Doublet near 6 ppm
C. Triplet near 3 ppm
D. Sharp singlet near 0.5 ppm

Question 27: Why are deuterated solvents used in proton NMR spectroscopy?

A. They dissolve samples better
B. They do not produce proton signals
C. They improve splitting patterns
D. They enhance peak areas

Question 28: Which of the following would result in a multiplet in ¹H NMR?

A. Proton with 3 equivalent neighbours
B. No adjacent protons
C. Proton near a methyl group only
D. Proton next to OH

Question 29: What chemical shift range would you expect for aromatic protons in ¹H NMR?

A. 0.5–2.0 ppm
B. 2.0–3.0 ppm
C. 6.5–8.0 ppm
D. 9.5–12.0 ppm

Question 30: What does a quartet pattern in ¹H NMR suggest about neighbouring protons?

A. 2 neighbours
B. 3 neighbours
C. 4 neighbours
D. No neighbours

Marking Key and Detailed Explanations – Chapter 37: Analytical Techniques

Q1: C. To adsorb compounds for separation
Explanation: The stationary phase holds components differently based on their polarity, enabling separation.

Q2: C. A solvent that carries the compounds up the plate
Explanation: The mobile phase in TLC is the solvent that moves via capillary action, helping separate the substances.

Q3: C. Rf = distance moved by solute / distance moved by solvent
Explanation: Rf is the ratio of distance travelled by compound to the solvent front from the baseline.

Q4: C. It strongly interacts with the stationary phase
Explanation: Strong interaction with the stationary phase slows down the movement, resulting in a lower Rf.

Q5: B. An inert gas
Explanation: In gas chromatography, the mobile phase is an unreactive carrier gas like helium or nitrogen.

Q6: B. Time taken for a substance to leave the column
Explanation: Retention time is the time between injection and detection of a compound.

Q7: C. Strong interaction with stationary phase
Explanation: Stronger interactions with the stationary phase delay movement through the column.

Q8: B. Non-polar liquid on a solid support
Explanation: The stationary phase is a non-polar high boiling liquid coated on solid particles inside the column.

Q9: C. A different compound in the mixture
Explanation: Each peak in a chromatogram represents a unique compound that was separated.

Q10: C. Colour of the compound
Explanation: Colour has no effect on retention time; polarity and volatility are the main influencers.

Q11: B. Carbon atoms in unique environments
Explanation: ¹³C NMR detects carbon atoms in chemically distinct environments.

Q12: A. 1
Explanation: Methane has four identical carbon-hydrogen bonds; only one environment.

Q13: D. Carbonyl carbon
Explanation: Carbonyl groups (like aldehydes/ketones) show up around 200 ppm in ¹³C NMR.

Q14: B. ¹³C atoms do not couple with other ¹³C atoms
Explanation: Because ¹³C is only ~1.1% abundant, coupling between ¹³C atoms is rare.

Q15: B. Number of unique carbon environments
Explanation: Each distinct environment gives a separate peak.

Q16: C. CDCl₃
Explanation: Deuterated solvents don’t interfere in ¹H NMR because they lack normal hydrogen.

Q17: B. Reference for chemical shift
Explanation: TMS gives a sharp signal at 0 ppm, used as a reference for shifts.

Q18: C. Number of peaks based on neighbouring protons
Explanation: The n+1 rule describes how neighbouring H atoms cause signal splitting.

Q19: C. 2 neighbours
Explanation: A triplet results from two equivalent neighbouring protons.

Q20: B. Number of equivalent hydrogen atoms
Explanation: Peak area ratios give information about proton quantities.

Q21: C. Aldehyde proton
Explanation: Aldehydes appear furthest downfield (typically 9–10 ppm).

Q22: B. Adjacent protons influencing magnetic environment
Explanation: Coupling arises due to spin-spin interactions between nearby protons.

Q23: B. Proton exchange occurred with O–H or N–H
Explanation: D₂O replaces H with D, removing the O–H or N–H peak.

Q24: C. Triplet
Explanation: The CH₃ protons feel the effect of 2 neighbouring CH₂ protons → triplet.

Q25: A. One hydrogen with no neighbouring protons
Explanation: A singlet means no adjacent hydrogens are present to cause splitting.

Q26: A. Broad singlet around 11–12 ppm
Explanation: Carboxylic acids show as a broad singlet at high ppm.

Q27: B. They do not produce proton signals
Explanation: Deuterium doesn’t resonate at the same frequency, avoiding interference.

Q28: A. Proton with 3 equivalent neighbours
Explanation: n = 3 neighbours → n+1 = 4 peaks = quartet (or multiplet if complex).

Q29: C. 6.5–8.0 ppm
Explanation: Aromatic protons typically fall in this range in ¹H NMR.

Q30: B. 3 neighbours
Explanation: Quartet splitting arises from three adjacent equivalent protons.