A Level H2 Chemistry Organic Chemistry Quiz

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A-Level Chemistry H2 Quiz - Organic Chemistry

Name: ___________________________
Class: ___________________________
Date: ___________________________
Score: _______ / 40

Duration: 60 minutes
Total Marks: 40
Instructions: Answer all 20 questions. Section A is short structured response. Section B requires mechanisms and reasoning. Section C involves synthesis and data interpretation. Show all working where applicable. Use the Data Booklet if needed.

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Section A: Fundamentals and Isomerism (Questions 1–5)

1. [2 marks] Define the term structural isomerism and give the molecular formula shared by propan-1-ol and methoxyethane.

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2. [2 marks] Draw the structural formula of the cis isomer of but-2-ene. Show clearly the relative positions of the methyl groups.

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3. [1 mark] State the IUPAC name of the compound with formula $\text{CH}_3\text{CH}(\text{OH})\text{CH}_2\text{CH}_3$.

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4. [2 marks] Explain, using the concept of chirality, why 2-bromobutane shows optical activity but butan-2-ol does not necessarily do so in a racemic mixture.

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5. [2 marks] A hydrocarbon has empirical formula $\text{CH}_2$ and relative molecular mass 56. Determine its molecular formula and state the homologous series to which it belongs.

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Section B: Reactions and Mechanisms (Questions 6–13)

6. [3 marks] Bromoethane reacts with aqueous potassium hydroxide to form ethanol. Write the overall equation and state the mechanism type. Explain one observable difference if ethanolic KOH were used instead.

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7. [4 marks] Draw the mechanism for the nucleophilic substitution of 2-bromopropane with $\text{OH}^-$ via an $\text{S}_\text{N}1$ pathway. Include curly arrows, the carbocation intermediate, and the final product.

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8. [3 marks] Propene reacts with HBr in the absence of peroxides. State the major product and explain the regioselectivity using Markovnikov’s rule.

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9. [3 marks] Acidified potassium dichromate(VI) oxidises propan-1-ol. Write the two-stage oxidation sequence with reagents/conditions and the final organic product.

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10. [2 marks] State the reagents and conditions needed to convert benzaldehyde to 1-phenylethanol.

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11. [4 marks] Ethanol can be dehydrated to ethene using concentrated $\text{H}_2\text{SO}_4$ at 170 °C. Draw a labelled diagram of a suitable setup and state the role of the acid.

Image pending generation: experimental_setup for Q11.

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12. [3 marks] Compare the hydrolysis rates of 1-bromobutane, 1-chlorobutane, and 1-iodobutane in aqueous ethanol. Explain your order in terms of bond enthalpy.

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13. [3 marks] State the product when ethanoyl chloride reacts with methylamine. Write the equation and name the functional group formed.

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Section C: Synthesis and Data Interpretation (Questions 14–20)

14. [2 marks] Give a two-step synthesis from chloroethane to propanoic acid. State reagents for each step.

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15. [3 marks] A student obtains an IR spectrum of an unknown carbonyl compound.

Image pending generation: graph for Q15.

State the functional group present and identify the compound as ethanoic acid or propanal. Explain.

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16. [3 marks] Polymerisation of propene gives polypropene. State the type of polymerisation and draw a two-repeat unit segment of the polymer chain showing the methyl side groups.

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17. [2 marks] Calculate the molar mass of the repeat unit of poly(chloroethene), PVC, given atomic masses: C = 12.0, H = 1.0, Cl = 35.5.

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18. [3 marks] Nitration of benzene requires a nitrating mixture. State the reagents, conditions, and the electrophile generated. Write the equation for electrophile formation.

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19. [3 marks] A peptide is formed from glycine and alanine. Draw the structure of the dipeptide Gly–Ala and state the type of linkage.

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20. [3 marks] Given the mass spectrum of an alkane shows a molecular ion peak at m/z = 72. Deduce the molecular formula and draw two possible structural isomers.

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A-Level Chemistry H2 Quiz - Organic Chemistry (Answer Key)

Total Marks: 40
Teaching notes are provided for each item. Marks are shown as [n].

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Q1. [2]

• Structural isomerism: compounds with the same molecular formula but different structural arrangements of atoms (different connectivity). [1]
• Shared molecular formula: $\text{C}_3\text{H}_8\text{O}$. [1]
  Teaching note: Propan-1-ol (chain alcohol) and methoxyethane (ether) have same atoms, different bonds. Common mistake: writing $\text{C}_3\text{H}_6\text{O}$ (that is for aldehydes/ketones).

Q2. [2]

• cis-but-2-ene: $\text{CH}_3$ groups on the same side of the double bond.
  Structure:
  $\text{H}_3\text{C}-\text{CH}=\text{CH}-\text{CH}_3$ with both $\text{CH}_3$ upward (or both downward). [2 for correct drawing]
  Teaching note: cis = same side; trans = opposite. Mark deducted if methyl groups shown opposite.

Q3. [1]

• Butan-2-ol. [1]
  Teaching note: OH on C2 of 4-carbon chain. IUPAC priority gives lowest locant to OH.

Q4. [2]

• 2-bromobutane has a chiral centre at C2 (attached to Br, H, $\text{CH}_3$, $\text{C}_2\text{H}_5$) → rotates plane-polarised light. [1]
• A racemic mixture of butan-2-ol contains equal (+) and (–) enantiomers, net rotation = 0, so no observable optical activity. [1]
  Teaching note: Chirality needs 4 different groups. Racemate cancels rotation.

Q5. [2]

• Empirical mass = 14; $56/14 = 4$ → molecular formula $\text{C}_4\text{H}_8$. [1]
• Homologous series: alkenes (or cycloalkanes). [1]
  Teaching note: $\text{C}_n\text{H}_{2n}$ fits alkene series.

Q6. [3]

• Equation: $\text{CH}_3\text{CH}_2\text{Br} + \text{KOH}(aq) \rightarrow \text{CH}_3\text{CH}_2\text{OH} + \text{KBr}$. [1]
• Mechanism: nucleophilic substitution ($\text{S}_\text{N}2$). [1]
• With ethanolic KOH (no water), elimination occurs → ethene + KBr (not substitution). [1]
  Teaching note: Solvent controls pathway: aqueous = substitution, alcoholic = elimination.

Q7. [4]
Mechanism ($\text{S}_\text{N}1$):

1. $\text{CH}_3\text{CHBrCH}_3 \rightarrow \text{CH}_3\text{CH}^+\text{CH}_3 + \text{Br}^-$ (slow, carbocation). [1]
2. Curly arrow from $\text{OH}^-$ lone pair to carbocation C. [1]
3. Product: $\text{CH}_3\text{CH}(\text{OH})\text{CH}_3$ (propan-2-ol). [1]
4. Correct curly arrows from C–Br bond to Br, and from OH to C shown. [1]
   Teaching note: Secondary halide can do $\text{S}_\text{N}1$; carbocation is planar intermediate.

Q8. [3]

• Major product: 2-bromopropane. [1]
• Markovnikov: H adds to C with more H; Br to more substituted C. [1]
• Intermediate: more stable secondary carbocation forms. [1]
  Teaching note: No peroxides → ionic addition, Markovnikov orientation.

Q9. [3]

1. $\text{CH}_3\text{CH}_2\text{CH}_2\text{OH} + [\text{O}] \xrightarrow{\text{K}_2\text{Cr}_2\text{O}_7/\text{H}^+} \text{CH}_3\text{CH}_2\text{CHO}$ (propanal). [1]
2. $\text{CH}_3\text{CH}_2\text{CHO} + [\text{O}] \rightarrow \text{CH}_3\text{CH}_2\text{COOH}$ (propanoic acid). [1]
3. Conditions: heat under reflux with acidified $\text{K}_2\text{Cr}_2\text{O}_7$. [1]
   Teaching note: Primary alcohol → aldehyde → carboxylic acid.

Q10. [2]

• Reagents: $\text{NaBH}_4$ (sodium borohydride) in methanol/water. [1]
• Conditions: room temperature, then acid workup. [1]
  Teaching note: Aldehyde + hydride reducing agent gives secondary alcohol.

Q11. [4]

• Diagram shows flask with ethanol + conc $\text{H}_2\text{SO}_4$, thermometer at 170 °C, delivery to gas jar. [2]
• Role of acid: catalyst and dehydrating agent (removes water). [1]
• Product: $\text{CH}_2=\text{CH}_2 + \text{H}_2\text{O}$. [1]
  Teaching note: Image must show temp 170 not 140 (140 gives ether).

Q12. [3]

• Order of hydrolysis rate: 1-iodobutane > 1-bromobutane > 1-chlorobutane. [1]
• C–I bond weakest (lowest bond enthalpy), C–Cl strongest. [1]
• Rate-determining step is C–X bond breaking; weaker bond = faster. [1]
  Teaching note: Bond enthalpies: C–Cl ~340, C–Br ~280, C–I ~240 kJ/mol.

Q13. [3]

• Product: N-methylethanamide ($\text{CH}_3\text{CONHCH}_3$). [1]
• Equation: $\text{CH}_3\text{COCl} + \text{CH}_3\text{NH}_2 \rightarrow \text{CH}_3\text{CONHCH}_3 + \text{HCl}$. [1]
• Functional group: amide. [1]
  Teaching note: Acyl chloride + amine → amide (nucleophilic acyl substitution).

Q14. [2]

• Step 1: $\text{CH}_3\text{CH}_2\text{Cl} + \text{KCN} \rightarrow \text{CH}_3\text{CH}_2\text{CN}$ (ethanenitrile). [1]
• Step 2: $\text{CH}_3\text{CH}_2\text{CN} + \text{H}_3\text{O}^+ / \text{heat} \rightarrow \text{CH}_3\text{CH}_2\text{COOH}$ (propanoic acid). [1]
  Teaching note: CN lengthens chain by 1 C; hydrolysis gives acid.

Q15. [3]

• Functional group: carboxylic acid (broad O–H + C=O). [1]
• Compound: ethanoic acid (not propanal) because broad 3300 = O–H of COOH. [1]
• Propanal would lack broad O–H and show aldehyde C–H ~2720. [1]
  Teaching note: Image shows broad 3300 + 1715 → acid, not aldehyde.

Q16. [3]

• Type: addition polymerisation. [1]
• Segment: $-\text{[CH}_2-\text{CH(CH}_3)\text{]}_n-$, draw two repeats with $\text{CH}_3$ on alternate C. [2]
  Teaching note: Double bond opens; side group stays on every other carbon.

Q17. [2]

• Repeat unit from $\text{CH}_2=\text{CHCl}$: $-\text{CH}_2-\text{CHCl}-$.
• $M = 2(12.0) + 3(1.0) + 35.5 = 24 + 3 + 35.5 = 62.5\ \text{g mol}^{-1}$. [2]
  Teaching note: Sum atoms in repeat unit, not monomer gas mass only.

Q18. [3]

• Reagents: conc $\text{HNO}_3$ + conc $\text{H}_2\text{SO}_4$. [1]
• Conditions: < 55 °C (avoid dinitration). [1]
• Electrophile: $\text{NO}_2^+$; equation: $\text{HNO}_3 + 2\text{H}_2\text{SO}_4 \rightarrow \text{NO}_2^+ + 2\text{HSO}_4^- + \text{H}_3\text{O}^+$. [1]
  Teaching note: $\text{H}_2\text{SO}_4$ generates nitronium ion.

Q19. [3]

• Glycine: $\text{H}_2\text{N-CH}_2\text{-COOH}$; Alanine: $\text{CH}_3\text{-CH(NH}_2)\text{-COOH}$.
• Dipeptide: $\text{H}_2\text{N-CH}_2-\text{CO-NH-CH(CH}_3)\text{-COOH}$. [2]
• Linkage: peptide (amide) bond. [1]
  Teaching note: Condensation releases $\text{H}_2\text{O}$ between carboxyl and amino.

Q20. [3]

• $M = 72$ → $\text{C}_5\text{H}_{12}$ (alkane $\text{C}_n\text{H}_{2n+2}$: $12n+2n+2=72 \rightarrow n=5$). [1]
• Two isomers: n-pentane; 2-methylbutane (or 2,2-dimethylpropane). [2]
  Teaching note: Draw chain and branched versions; all $\text{C}_5\text{H}_{12}$.