MChem Master of Chemistry — Questions and Answers

Question 1: For a chain reaction mechanism, the steady-state approximation applied to radical intermediates gives the rate law. Which step determines the overall reaction order for a long chain?

The branching step
The propagation step (Correct answer)
The termination step
The initiation step

Correct answer: The propagation step

In a long chain where the chain length >> 1, propagation steps dominate and determine the observed rate law and reaction order.

Question 2: Organic molecules with the element _________ make up hydrocarbons.

Oxygen
Carbon
Both hydrogen and carbon (Correct answer)
Hydrogen

Correct answer: Both hydrogen and carbon

The name 'hydrocarbon' itself indicates its composition: 'hydro' refers to hydrogen, and 'carbon' refers to carbon. Hydrocarbons are organic compounds composed solely of hydrogen and carbon atoms. They form the fundamental framework of many organic molecules, serving as the basis for other functionalized organic compounds.

Question 3: In the Contact Process for sulfuric acid production, what is the role of vanadium pentoxide (V2O5)?

It removes moisture from the gas stream
It absorbs SO3 into oleum
It catalyzes the oxidation of SO2 to SO3 (Correct answer)
It converts H2S to SO2

Correct answer: It catalyzes the oxidation of SO2 to SO3

V2O5 catalyzes the key step SO2 + ½O2 → SO3 by cycling between V5+ and V4+ oxidation states.

Question 4: In DNA replication, what is the chemical basis for the 3'→5' proofreading activity of DNA polymerase?

A separate exonuclease enzyme removes mismatched bases after replication
DNA polymerase has an intrinsic 3'→5' exonuclease domain that excises incorrectly incorporated nucleotides (Correct answer)
The DNA helicase corrects mismatches as it unwinds the double helix
Mismatch repair proteins act during replication to immediately fix errors

Correct answer: DNA polymerase has an intrinsic 3'→5' exonuclease domain that excises incorrectly incorporated nucleotides

DNA polymerase III possesses a 3'→5' exonuclease domain that recognizes and excises mismatched 3'-terminal nucleotides, then re-synthesizes the correct sequence.

Question 5: In molecular dynamics (MD) simulations, what does the NPT ensemble maintain constant?

Number of particles, energy, and pressure
Energy, volume, and temperature
Number of particles, volume, and temperature
Number of particles, pressure, and temperature (Correct answer)

Correct answer: Number of particles, pressure, and temperature

The NPT (isothermal-isobaric) ensemble keeps the number of particles (N), pressure (P), and temperature (T) constant.

Question 6: Which one compresses more easily?

solid
liquid
gas (Correct answer)
solution

Correct answer: gas

Gases are the most compressible state of matter because their particles are widely spaced and experience very weak intermolecular forces. This allows them to be forced into a much smaller volume under pressure. Solids and liquids have particles that are already closely packed, making them significantly less compressible.

Question 7: For a rigid rotor, the rotational energy levels are given by E_J = BJ(J+1). The degeneracy of level J is:

J
2J+1 (Correct answer)
2J
J(J+1)

Correct answer: 2J+1

Each rotational level J has 2J+1 degenerate M_J substates ranging from −J to +J.

Question 8: Which end-group analysis method is most appropriate for determining the number-average molecular weight of a low-molecular-weight polyester (Mn < 5,000 g/mol)?

¹H NMR end-group analysis (Correct answer)
Gel permeation chromatography (GPC)
Osmometry using a semi-permeable membrane
Dynamic light scattering (DLS)

Correct answer: ¹H NMR end-group analysis

¹H NMR end-group analysis quantifies distinct end-group signals relative to backbone repeat-unit signals, providing accurate Mn for low-molecular-weight polymers where end groups are a significant fraction of the signal.

Question 9: Which spectroscopic feature in FTIR is most diagnostic for identifying a polyurethane?

A strong C=O stretch near 1730 cm⁻¹ and N-H stretch near 3300 cm⁻¹ (Correct answer)
A broad O-H stretch at 2500-3300 cm⁻¹ typical of carboxylic acids
A strong C-F stretch at 1100 cm⁻¹
A sharp C≡N stretch at 2200 cm⁻¹

Correct answer: A strong C=O stretch near 1730 cm⁻¹ and N-H stretch near 3300 cm⁻¹

Polyurethanes are identified by the N-H stretch (~3300 cm⁻¹) from the urethane linkage and the C=O carbonyl stretch (~1700-1730 cm⁻¹) of the carbamate group.

Question 10: Select the force or forces at play in chromatography.

Electrostatic
All of them (Correct answer)
London
Hydrogen Bonding

Correct answer: All of them

Chromatography relies on a variety of intermolecular forces to achieve the separation of mixture components. These forces include electrostatic interactions (ionic attractions), hydrogen bonding, and London dispersion forces (a type of van der Waals force). The specific combination and strength of these interactions between the analytes and the stationary and mobile phases dictate the separation efficiency.

Question 11: In chemical biology, what is a 'warhead' in the context of covalent inhibitor drug design?

The fluorescent reporter group on a probe molecule
A prodrug moiety that is cleaved in vivo to release the active drug
The pharmacophore that determines binding specificity
A reactive electrophilic group that forms a covalent bond with a nucleophilic residue in the target protein (Correct answer)

Correct answer: A reactive electrophilic group that forms a covalent bond with a nucleophilic residue in the target protein

Warheads (e.g., acrylamides, chloroacetamides) are reactive electrophiles that covalently modify active-site nucleophiles (e.g., Cys, Lys), providing irreversible or slow-reversible inhibition.

Question 12: Of the following machines, which one doesn't require a chemical separation method?

Water cooler
The washing machine
Refrigerator
Coffee machine (Correct answer)

Correct answer: Coffee machine

A coffee machine primarily uses physical filtration to separate solid coffee grounds from the brewed liquid. Unlike a washing machine, where detergents chemically interact with dirt to facilitate its separation from fabric, the coffee machine's core separation process does not rely on chemical reactions or chemical property changes. Water coolers and refrigerators do not perform separation as their primary function.

Question 13: In density functional theory (DFT), the exchange-correlation functional approximates which quantity?

Electrostatic Coulomb energy
Kinetic energy of electrons
Many-body exchange and correlation effects (Correct answer)
Nuclear repulsion energy

Correct answer: Many-body exchange and correlation effects

The exchange-correlation functional in DFT approximates the complex many-body exchange and correlation effects that cannot be computed exactly.

Question 14: Which of the following is not an aromatic hydrocarbon property?

These compounds have very good aromaticity
These compounds have excellent stability
These compounds do not undergo nucleophilic substitutions but they undergo electrophilic substitutions (Correct answer)
There exists a strong ratio between carbon and hydrogen

Correct answer: These compounds do not undergo nucleophilic substitutions but they undergo electrophilic substitutions

Aromatic hydrocarbons are highly stable due to their delocalized pi electron system and exhibit a high carbon-to-hydrogen ratio. They are notoriously unreactive towards nucleophilic substitution under typical conditions because their electron-rich ring repels nucleophiles. Instead, their characteristic reactions are electrophilic aromatic substitutions, where an electrophile attacks the electron-rich ring. Therefore, the statement accurately describes their reactivity pattern, making it a true property.

Question 15: The rate at which phenolphthalein fades in basic solution is

1st order (Correct answer)
2nd order
3rd order
0th order

Correct answer: 1st order

The fading of phenolphthalein in a basic solution is a classic example of a chemical reaction whose rate depends on the concentration of the reactants. Experimental studies typically show that this reaction follows first-order kinetics with respect to phenolphthalein, meaning its rate of disappearance is directly proportional to its concentration.

Question 16: Which of the following factors most destabilizes a cyclopropane ring relative to cyclohexane?

Transannular strain from non-bonded interactions across the ring
Angle strain from compressed C–C–C bond angles (~60°) and torsional strain from eclipsed C–H bonds (Correct answer)
Large gauche interactions between substituents
Steric strain from axial substituents

Correct answer: Angle strain from compressed C–C–C bond angles (~60°) and torsional strain from eclipsed C–H bonds

Cyclopropane suffers severe angle strain (ideal sp³ angle is 109.5° vs. actual ~60°) and torsional strain because all adjacent C–H bonds are forced into an eclipsed conformation.

Question 17: What method of separation is employed when a chemical reaction aids in separation during a separation operation?

Fractional crystallization
Distillation
Reactive distillation (Correct answer)
Fractional distillation

Correct answer: Reactive distillation

Reactive distillation is a specialized separation method that integrates a chemical reaction and distillation into a single unit operation. In this process, the chemical reaction occurs simultaneously with the separation of products and reactants by distillation. This combination can enhance reaction conversion, improve selectivity, and reduce overall process costs by continuously removing products or reactants.

Question 18: Which electroanalytical technique applies a linearly varying potential and measures the resulting current to determine analyte concentration from peak current?

Impedance spectroscopy
Chronoamperometry
Coulometry at controlled potential
Linear sweep voltammetry (LSV) (Correct answer)

Correct answer: Linear sweep voltammetry (LSV)

LSV scans potential linearly with time and records faradaic current peaks whose height is proportional to analyte concentration via the Randles-Ševčík equation.

Question 19: What is the role of coenzyme A (CoA) in metabolic pathways?

It activates and transfers acyl groups in fatty acid and carbohydrate metabolism (Correct answer)
It carries hydride ions between oxidation reactions
It carries amino acids during protein synthesis
It donates methyl groups in methylation reactions

Correct answer: It activates and transfers acyl groups in fatty acid and carbohydrate metabolism

CoA forms high-energy thioester bonds with acyl groups (e.g., acetyl-CoA), activating them for transfer reactions in the citric acid cycle, fatty acid synthesis, and β-oxidation.

Question 20: The 4-amino-5-nitrosopyrimidine and phenylacetonitrile process was originally used to create which of the following drugs?

Trimethoprim (Correct answer)
Triamterene
Alprazolam
Sulfamerazine

Correct answer: Trimethoprim

Trimethoprim is an antibacterial drug that inhibits bacterial dihydrofolate reductase, an enzyme essential for bacterial DNA synthesis. Its synthesis involves specific pyrimidine intermediates, and the reaction between 4-amino-5-nitrosopyrimidine and phenylacetonitrile is a known synthetic route to construct the pyrimidine core of the trimethoprim molecule, leading to the final drug product.

Question 21: Which of the following organic compound members is the most basic?

Methane (Correct answer)
Formaldehyde
Methanol
Formic acid

Correct answer: Methane

Methane (CH4) is the simplest alkane and the most basic organic compound, consisting of one carbon atom bonded to four hydrogen atoms. It is the fundamental building block from which more complex organic molecules can be derived. The other options are more complex, containing additional atoms like oxygen or more carbon atoms.

Question 22: Which of the following separation methods is based on volatility differences?

Crystallization
Fractional crystallization
Magnetic separation
Distillation (Correct answer)

Correct answer: Distillation

Distillation is a fundamental separation technique that exploits differences in the volatility of components within a liquid mixture. By heating the mixture, the more volatile components preferentially vaporize, and these vapors are then condensed and collected. This difference in boiling points allows for the effective separation and purification of substances.

Question 23: In atom transfer radical polymerization (ATRP), what component serves as the persistent radical?

The Cu(II) complex (oxidized metal halide) (Correct answer)
The alkyl halide initiator
The carbon-centered propagating radical
The ligand coordinated to copper

Correct answer: The Cu(II) complex (oxidized metal halide)

In ATRP, the Cu(II)/L complex is the persistent (stable) radical that caps the propagating chain, maintaining low active radical concentration via the persistent radical effect.

Question 24: if 2g of NaCl is dissolved in 20g of water, then the solution's percentage is

5%
9% (Correct answer)
7%
12%

Correct answer: 9%

To calculate the percentage concentration (mass/mass), we use the formula: (mass of solute / total mass of solution) * 100%. Here, the mass of solute (NaCl) is 2g, and the mass of solvent (water) is 20g. The total mass of the solution is 2g + 20g = 22g. Therefore, the percentage is (2g / 22g) * 100% ≈ 9.09%, which rounds to 9%.

Question 25: Surface-adsorbed chemicals are known as surfactants, and surface tension is

decreased (Correct answer)
increased
varied
remain constant

Correct answer: decreased

Surfactants are compounds that, when added to a liquid, reduce its surface tension. They achieve this by adsorbing at the liquid-air or liquid-liquid interface, disrupting the cohesive forces between liquid molecules at the surface. This property makes them useful in applications like detergents, emulsifiers, and wetting agents.

Question 26: Which spectroscopic method directly probes the oxidation state and local coordination environment of a metal in a heterogeneous catalyst?

Raman spectroscopy
Electron paramagnetic resonance (EPR)
X-ray absorption spectroscopy (XANES/EXAFS) (Correct answer)
UV-Vis diffuse reflectance spectroscopy

Correct answer: X-ray absorption spectroscopy (XANES/EXAFS)

XANES gives oxidation state information via edge energy, while EXAFS provides local coordination number, bond distances, and identity of neighbors around the absorbing metal.

Question 27: In NMR spectroscopy, the chemical shift δ (in ppm) is defined relative to a reference compound (TMS). A nucleus with greater electron density around it will resonate at:

Lower δ (upfield) (Correct answer)
The same δ regardless of shielding
A δ that depends only on the gyromagnetic ratio
Higher δ (downfield)

Correct answer: Lower δ (upfield)

Greater electron density increases diamagnetic shielding, reducing the effective field at the nucleus and shifting the resonance upfield (lower δ).

Question 28: Spectrogram produced by spectroscopic measurements is the outcome of the

Radiations not absorbed
Radiations absorbed (Correct answer)
Radiations emitted only
Radiations absorbed only

Correct answer: Radiations absorbed

In absorption spectroscopy, a spectrogram (or spectrum) is generated by measuring the amount of light absorbed by a sample across different wavelengths. The resulting graph shows peaks and troughs that correspond to specific wavelengths of radiation that are absorbed by the sample's molecules, providing unique information about its chemical composition and structure.

Question 29: In the Diels-Alder reaction, which diene conformation is required for the reaction to proceed?

s-trans
gauche
s-cis (Correct answer)
anti-periplanar

Correct answer: s-cis

The diene must adopt the s-cis conformation so that both terminal carbons can interact with the dienophile in a concerted [4+2] cycloaddition.

Question 30: Which of the following types of enzyme inhibitors is irreversible?

Non competitive inhibitor
Competitive inhibitor
uncompetitive inhibitor
Suicide inhibitor (Correct answer)

Correct answer: Suicide inhibitor

Suicide inhibitors, also known as mechanism-based inhibitors, are a type of irreversible enzyme inhibitor. These molecules are initially unreactive but are processed by the target enzyme's active site, converting them into a highly reactive species. This reactive intermediate then forms a covalent bond with a functional group in the enzyme's active site, permanently inactivating the enzyme.

MChem Master of Chemistry

The MChem (Master of Chemistry) is a 4-year integrated undergraduate/postgraduate degree accredited by the Royal Society of Chemistry (RSC), assessing students across core and advanced chemistry disciplines including organic, inorganic, physical, industrial, biochemical, and computational chemistry.

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35 min

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70%

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