This "cheat sheet" provides a guide to answering subjective questions in Paper 2 for AS-Level Chemistry. Format your answers according to what is written in this webpage.
1. Comparison of atomic radius / IE
[Going down the group]
① Positive nuclear charge increases
② Electron shielding increases
③ Weaker nuclear attraction for outer shell e-
④ No. of e- occupied shells increases
⑤ Weaker nuclear attraction for outer shell e-
[Going across the period]
① Positive nuclear charge increases
② Electron shielding same
2. Comparison between melting / boiling point
① X is giant ionic / giant covalent / simple molecule and Y is __________
② Covalent / electrostatic forces of attraction / LDF / permanent dipole-dipole / hydrogen bonding occurs between X atoms / ions / molecules and __________ acts between Y
③ More heat energy is required to break / overcome __________ bonds / forces in X than __________ bonds / forces in Y.
④ Less energy required to remove e- from __________ than __________
⑤ More energy required to remove e- from __________
3. Discrepancies in IE
① IE is removed from p shell of higher energy level in Al
② Smaller nuclear attraction number
③ Spin-pair repulsion between 2 electrons in s
④ e- is removed from full orbital in s but half-filled 3p orbital in P.
⑤ Between Al & Mg
⑥ Between P and S
4. Describing Observations
① Steamy fumes - HCl gas
② Solid produced - product of reaction
5. Explaining why X is a molecule and not ionic compound
① Hydrolysis occurs → simple molecule
② Low mp and bp → weak IMF / hydrogen bonds → simple molecule
6. Reagents for Organic Reactions
① Oxidation → acidified aqueous KMnO₄ / K₂Cr₂O₇
② Reduction → NaBH₄ / LiAlH₄
③ 2-4 - DNPH → carbonyl detection
④ Alkaline I₂ → tri-iodomethane
⑤ HCN in KCN / NaCN in H₂SO₄ → CN nucleophilic addition
⑥ KCN in ethanol, heated → CN nucleophilic substitution
⑦ Aqueous concentrated NH₃ in ethanol → NH₃ substitution
⑧ NaOH (aq) warmed → OH substitution
⑨ NaOH ethanolic, heated strongly → OH elimination
⑩ dilute HCl / H₂SO₄ → hydrolysis
⑪ conc. HCl / H₂SO₄ → dehydration of alcohol and esterification
⑫ Tollen's / Fehlings → aldehyde to ketone
7. Explaining why something becomes a major product
① X forms primary / secondary / tertiary carbocation intermediates while Y forms ____
② X carbocation is more stable than Y
③ X has more alkyl groups, so more e- releasing groups and stronger positive inductive effect.
④ _____ is the major product because it has a more stable carbocation intermediate.
8. Explaining why halogenoalkanes become more reactive (can be applied to similar questions)
① C-X bond energy decreases down group
② atomic radius increases, bigger distance between nucleus and shared e-
③ nuclear attraction on shared e- pair decreases.
④ C-X bond is broken more easily, so lower activation energy
9. Le Chatelier's Principle
① Equilibrium shifts to the left/right
② forward/backward reaction is exothermic
or
② ____ moles of gas on RHS and ____ moles of gas on LHS
③ system moves to minimise the change.
10. Talking about catalysts
① is a homogenous / heterogenous catalyst because it is in the same / diff phase as reactants.
② speeds up reaction by lowering Ea (alternative pathway of lower Ea), so more successful collisions
11. Formation of hybridisation bonds
① X shows sp / sp² / sp³ hybridization
② s / p / sp / sp² / sp³ orbitals overlap to form pi/sigma bonds
Note: single bonds → sp³, double bonds → sp², triple bonds → sp
12. Formation of stereoisomers
① pair of enantiomers formed, have two non-superimposable mirror images
② nucleophile attack from above or below the bond.
13. Explaining why X is a geometric isomer
① Have 2 carbon atoms in the C=C bond that are both attached to two diff groups.
14. Explaining why X is a Bronsted-Lowry base/acid
① X donates a proton, making it a Bronsted-Lowry acid
or
① X accepts a proton, making it a Bronsted-Lowry base
16. Infrared absorption spectra (Identification)
① X is ____ because it has ____ and ____ bonds.
② The spectra shows a peak at ____ which corresponds to ____ bond.
16. Infrared absorption spectra (When molecules change)
① Concentration of X decreases and concentration of Y increases.
② X contains ____ bond and Y contains ____ bond.
③ ____ peak corresponding to ____ bond disappears
④ ____ peak corresponding to ____ bond appears