VCAA Chemistry How are organic compounds analysed and used?

This incorrect answer is obtained by mistakenly swapping the volumes of the acid and base in the concentration calculation.

This error occurs if the volumes of the acid and base are swapped and the 1:3 stoichiometric ratio between citric acid and NaOH is ignored.

This incorrect result comes from multiplying the moles of NaOH by 3 instead of dividing by 3 to find the moles of the triprotic citric acid.

3-methylbutanoic acid has four unique sets of protons, which would produce a singlet (OH), a doublet (CH3 groups), a multiplet/nonet (CH), and another doublet (CH2).

2-chloro-2-methylpropane has only one unique set of protons (nine equivalent methyl protons), which would produce a single peak (singlet) in its $^1\text{H}$ NMR spectrum.

1,2-dichloro-2-methylpropane has two unique sets of protons that are not adjacent to any other protons, which would result in a spectrum with two singlets.

Zwitterions are molecules with both positive and negative charges that net to zero, typically occurring at an amino acid's isoelectric point. In highly acidic conditions, amino acids become positively charged cations, not zwitterions.

Acids do not esterify enzymes into smaller molecules. Breaking down an enzyme's protein chain into smaller molecules would involve the hydrolysis of peptide bonds, not esterification.

While acidic conditions do protonate carboxylate groups into neutral carboxyl groups, this is only a partial explanation. The loss of enzyme effectiveness is due to the overall change in charges across all ionizable groups, which disrupts the active site.

Although 2-methylbutan-2-ol is a tertiary alcohol and would not be oxidized, its molecular formula is C$_5$H$_{12}$O, which does not match the given formula of C$_4$H$_{10}$O.

3-methylbutan-2-ol has the incorrect molecular formula (C$_5$H$_{12}$O) and is a secondary alcohol, which would be oxidized and turn the dichromate solution green.

While butan-2-ol has the correct molecular formula, it is a secondary alcohol. It would be oxidized to a ketone, causing the dichromate solution to change colour from orange to green.

This option is incorrect because it does not include the characteristic absorption range for an amide C=O bond (1630–1680 cm$^{-1}$).

This option is incorrect because it misses the absorption band for the amide C=O stretch, which occurs at 1630–1680 cm$^{-1}$.

This option is incorrect because it lacks the correct absorption range for a ketone C=O bond, which typically absorbs between 1680–1850 cm$^{-1}$.

Carbohydrates are organic compounds like sugars and fibers used primarily for energy and structure, not for catalyzing reactions.

Starches are complex carbohydrates (polysaccharides) used for energy storage in plants, whereas enzymes are the proteins that might break them down.

Lipids include fats, oils, and waxes used for long-term energy storage and membrane structure, but they do not function as biological catalysts.

This is a solution of Iron(III) nitrate. Neither $Fe^{3+}$ nor $NO_3^-$ ions react with bromine water, so the solution would not be decolourised.

Chloride ions ($Cl^-$) cannot reduce bromine ($Br_2$) because chlorine is a stronger oxidising agent than bromine. Therefore, no reaction occurs to remove the bromine colour.

Solvent extraction relies on differences in solubility, which would likely be ineffective here since both ethanol and the other compounds are polar and may dissolve in similar solvents.

Simple distillation is only effective for separating liquids with significantly different boiling points (typically a difference of at least 25°C).

Adding solvent extraction is unnecessary and less efficient, as fractional distillation alone is the standard and most effective method for separating liquids with similar boiling points.

Primary structure refers to the linear sequence of amino acids held together specifically by covalent peptide bonds, not by the various side-chain interactions listed.

Secondary structure, such as $\alpha$-helices and $\beta$-sheets, is primarily stabilized by hydrogen bonds between the backbone amide and carbonyl groups, rather than interactions between side chains.

Quaternary structure refers specifically to the arrangement of multiple polypeptide subunits; while these forces hold subunits together, the question describes the forces defining the 3D fold of a single chain (tertiary structure).

This is incorrect because Statement I is true and Statement II is false. Pure substances have sharp melting points, so a broad range of >4 °C indicates a mixture, but a low melting point alone does not guarantee the presence of a mixture.

This is incorrect because Statement II is false. While impurities do cause melting point depression, a lower melting point could also result from thermometer miscalibration or the sample being a completely different pure compound.

This is incorrect because Statement I is true. A pure substance typically melts over a narrow range of 1-2 °C, so a sample melting over a range of more than 4 °C is definitively a mixture.

Vaporising the sample is a specific requirement for gas chromatography (GC), but it is not used in liquid chromatography techniques like HPLC.

A calibration curve is used to determine the concentration or amount of a component (quantitative analysis), whereas retention time is used to identify the component itself (qualitative analysis).

A high retention time means the component moves slowly through the column, which indicates it has a strong attraction (affinity) to the stationary phase, not the mobile phase.

Incorrect. Denaturation can be caused by many other factors besides temperature and acids, such as bases, heavy metals, organic solvents, and mechanical agitation.

Incorrect. Denaturation is most commonly an irreversible process, such as cooking an egg, rather than a reliably reversible change.

Incorrect. Denaturation does not break the covalent peptide bonds of the primary structure; a different process called hydrolysis is required to break down a protein's primary sequence.

This incorrect volume results from using a 1:5 stoichiometric ratio instead of the correct 2:5 ratio of MnO$_4^-$ to H$_2$O$_2$.

This incorrect answer results from applying the stoichiometric ratio upside down (5:2 instead of 2:5) and making a decimal place error.

This calculation assumes a 1:1 stoichiometric ratio between H$_2$O$_2$ and KMnO$_4$, failing to account for the 2:5 ratio in the balanced equation.

IR radiation causes changes in the vibrational states of molecules, not the spin states of electrons (which is associated with Electron Paramagnetic Resonance spectroscopy).

The wavenumber of a bond's vibration depends on both the bond strength (force constant) and the reduced mass of the atoms involved, as described by Hooke's Law.

Transmittance and absorbance are inversely related; high transmittance means that most of the light passed through the sample, indicating low absorption.

Primary structure refers to the linear sequence of amino acids connected by covalent peptide bonds, not hydrogen bonds.

Tertiary structure is the overall 3D shape determined primarily by interactions between amino acid side chains (R-groups), such as disulfide bridges, hydrophobic interactions, and ionic bonds.

Quaternary structure involves the arrangement of multiple polypeptide subunits held together by inter-chain interactions, rather than intra-chain bonding within a single backbone.