GCE Advanced Level (A-Levels) Chemistry Flashcards

24 sample cards from the Chemistry deck

Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.

1. Define homologous series.

   A family of organic compounds with the same general formula and functional group, differing by $\ce{CH2}$, showing a gradual change in physical properties and similar chemical reactions.

2. Distinguish between empirical and molecular formula.

   The empirical formula is the simplest whole-number ratio of atoms of each element; the molecular formula is the actual number of each type of atom in a molecule.

3. Define structural isomers and stereoisomers.

   Structural isomers have the same molecular formula but different structural arrangements of atoms; stereoisomers have the same structure but a different spatial arrangement (e.g. E/Z or optical isomers).

4. Why are E/Z (cis-trans) isomers possible in alkenes but not alkanes?

   The $\ce{C=C}$ double bond cannot rotate; if each carbon carries two different groups, the groups are locked in different spatial positions, giving E/Z isomers.

5. State the mechanism and reagent for the reaction of bromine with ethene.

   Electrophilic addition: $\ce{C2H4 + Br2 -> C2H4Br2}$ (1,2-dibromoethane), the basis of the bromine water test for unsaturation.

6. What is the mechanism of the reaction of methane with chlorine in UV light, and why is it limited?

   Free-radical substitution (initiation, propagation, termination); it gives a mixture of products and is hard to control as further substitution occurs.

7. Name the type of reaction and product when a primary alcohol is oxidised with acidified potassium dichromate(VI) and distilled off immediately.

   Oxidation to an aldehyde; e.g. $\ce{CH3CH2OH ->[\text{[O]}] CH3CHO + H2O}$; the orange dichromate turns green ($\ce{Cr^{3+}}$).

8. How do you distinguish an aldehyde from a ketone using Tollens' reagent?

   An aldehyde reduces Tollens' reagent (ammoniacal silver nitrate) producing a silver mirror; a ketone gives no reaction.

9. Give the structure of the carboxyl functional group and the products of its reaction with a carbonate.

   $\ce{-COOH}$; reaction with a carbonate gives a carboxylate salt, water and carbon dioxide (effervescence), e.g. $\ce{2CH3COOH + Na2CO3 -> 2CH3COONa + H2O + CO2}$.

10. What makes benzene resistant to addition reactions, favouring substitution?

    Its delocalised ring of six $\pi$-electrons is energetically stable; substitution preserves this delocalisation whereas addition would disrupt it.

11. Name the mechanism and product when benzene reacts with a mixture of concentrated $\ce{HNO3}$ and $\ce{H2SO4}$.

    Electrophilic substitution (nitration) producing nitrobenzene $\ce{C6H5NO2}$; the electrophile is the nitronium ion $\ce{NO2+}$.

12. How are amines classified as primary, secondary and tertiary, and how can they act as bases?

    By the number of carbon groups attached to nitrogen (one, two, three); the nitrogen lone pair accepts a proton, so amines act as Bronsted-Lowry bases.

13. Compare addition and condensation polymerisation.

    Addition polymerisation joins unsaturated monomers ($\ce{C=C}$) with no loss of atoms; condensation polymerisation joins monomers with two functional groups, eliminating a small molecule (e.g. $\ce{H2O}$ or $\ce{HCl}$) such as in polyesters and polyamides.

14. What links does an ester and an amide formation each involve in condensation polymers?

    Polyesters contain the ester linkage $\ce{-COO-}$ (from diol + dicarboxylic acid); polyamides contain the amide linkage $\ce{-CONH-}$ (from diamine + dicarboxylic acid).

15. What structural information does infrared (IR) spectroscopy provide?

    It identifies functional groups by the wavenumbers of bonds that absorb IR radiation, e.g. a broad $\ce{O-H}$ in carboxylic acids ($2500$-$3300\ \text{cm}^{-1}$) and $\ce{C=O}$ around $1700\ \text{cm}^{-1}$.

16. In a mass spectrum, what does the molecular ion peak (M$^+$) tell you, and what causes the M+1 peak?

    The M$^+$ peak gives the relative molecular mass; the small M+1 peak is due to the presence of the $\ce{^{13}C}$ isotope.

17. What does the number of peaks in a $^1$H NMR spectrum indicate, and what does splitting (the n+1 rule) reveal?

    The number of peaks shows the number of chemically different hydrogen environments; splitting into $n+1$ lines reveals $n$ hydrogens on adjacent carbon atoms.

18. In NMR spectroscopy, what is the reference standard and why is TMS used?

    Tetramethylsilane (TMS, $\ce{Si(CH3)4}$) is the standard set at $\delta = 0$; it is inert, volatile, non-toxic and gives a single sharp peak from 12 equivalent protons away from most other signals.

19. How does paper/thin-layer chromatography separate components, and what is the $R_f$ value?

    Separation depends on the differing affinities of components for the mobile and stationary phases; $R_f = \dfrac{\text{distance moved by spot}}{\text{distance moved by solvent front}}$.

20. What is the difference between the stationary and mobile phases in chromatography?

    The stationary phase is fixed (e.g. paper, silica); the mobile phase (a liquid or gas) moves through it carrying the components, which separate according to their relative attraction to each phase.

21. What test and result identifies a halide ion using silver nitrate solution?

    Add dilute $\ce{HNO3}$ then $\ce{AgNO3(aq)}$: $\ce{Cl-}$ gives a white precipitate, $\ce{Br-}$ cream, $\ce{I-}$ yellow; solubility in ammonia then confirms (chloride dissolves in dilute, bromide in concentrated, iodide insoluble).

22. How do you test for a carbonate ion and confirm the gas evolved?

    Add dilute acid; effervescence of $\ce{CO2}$ occurs ($\ce{CO3^2- + 2H+ -> H2O + CO2}$); bubbling the gas through limewater turns it cloudy.

23. State the test and positive result for ammonium ions ($\ce{NH4+}$).

    Warm with sodium hydroxide solution; ammonia gas is released which turns damp red litmus paper blue: $\ce{NH4+ + OH- -> NH3 + H2O}$.

24. How is sulfate ($\ce{SO4^2-}$) identified in solution?

    Add dilute $\ce{HCl}$ then barium chloride solution; a white precipitate of barium sulfate forms: $\ce{Ba^2+ + SO4^2- -> BaSO4}$.

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