280 against a target of 285. Five marks short — and the five marks are sitting in Q78, which you answered correctly and then ticked twice. Credit that one and the paper is exactly on target at 285. Everything below the first table is about the other seven, and three of those seven were questions the paper itself rated easy.
Where the marks went
Difficulty
Right
Out of
Accuracy
Easy
17
20
85%
85%
Moderate
40
42
95%
95%
Hard
15
18
83%
83%
That is the wrong way round. A paper is normally lost on its hard questions; this one was lost on its easy ones. Moderate 95 per cent against easy 85 per cent says the chemistry is there and the recall of plain reagent facts is not.
Section
Right
Out of
Lost on
Classification, Nomenclature and Preparation
17
20
Q16, Q17, Q18
Properties and Nucleophilic Substitution
20
22
Q30, Q42
Stereochemistry, Elimination and Metals
15
16
Q55
Haloarenes and Polyhalogen Compounds
20
22
Q70, Q78
What actually went wrong
Seven wrong answers, but not seven separate problems. Counting a wrong answer as a five-mark swing against a right one, 40 marks were lost in all. They fall into four groups, and the first two account for 25 of those 40.
15 marks · Q17, Q30, Q55
Three easy facts, fifteen marks
All three are one-line reagent facts, all three were marked easy on the paper, and all three were lost. Nothing here needs reasoning — each is a pair of names that has to be known cold. This is where the paper was actually decided: your moderate questions came in at 95 per cent and your easy ones at 85.
10 marks · Q42, Q70
One idea, twice: a dependency written backwards
Both multi-statement questions failed the same way. In each you kept two true statements, dropped a third true one, and accepted a false one — and in both cases the false statement you accepted reversed a dependency. In Q42, that an SN1 rate responds to the nucleophile. In Q70, that chlorobenzene is more reactive than chloromethane. These are not two mistakes. They are one habit: a statement that names a relationship is accepted without checking which way the relationship runs.
5 marks · Q18
The true statement that is not the reason
The option you chose was factually correct. It was not the cause. In any question that asks why something happens — and in every assertion–reason question — a true statement still has to be tested against the thing it is supposed to explain.
5 marks · Q16
One naming pair
Vicinal and geminal. Worth two minutes and then it is gone for good.
5 marks · Q78
And one that was not a chemistry mistake at all
Q78 carries two complete ticks, on (B) and on (D), with neither crossed out. (D) is right. You knew it. An OMR reads two responses as an invalid answer and takes a mark off, so a question you had solved turned into −1 instead of +4.
Question by question
Q16Classification, Nomenclature and Preparation · Preparation from hydrocarbons · moderate · trap: vicinal vs geminal
Addition of Br2 in CCl4 to an alkene gives
(A) a bromoalkane and HBr
(B) a geminal dihalide✓ YOUR ANSWER
(C) a vicinal dihalideCORRECT
(D) an allylic bromide
Bromine is a two-atom reagent adding to a two-atom double bond: one Br lands on each of the two neighbouring carbons. Two halogens on neighbouring carbons is vicinal (vicinus, next door). Two halogens on the same carbon is geminal (gemini, twins). A geminal dihalide would need both bromines to reach the same carbon, which addition across a double bond cannot do.
vicinal = next door · geminal = twins on one carbon
Q17Classification, Nomenclature and Preparation · Halogen exchange · easy · trap: the reagent half-remembered
The Finkelstein reaction converts an alkyl chloride or bromide into an alkyl iodide using
(A) NaI in dry acetoneCORRECT
(B) SbF3 in ether
(C) KI in aqueous ethanol✓ YOUR ANSWER
(D) AgF in boiling water
Finkelstein is NaI in dry acetone. Both halves matter and both were wrong here. It must be the sodium salt, because the whole reaction works by NaCl and NaBr falling out of solution, and it must be dry acetone, because water would dissolve them again and the equilibrium would sit still.
Finkelstein = NaI + dry acetone. Not KI, not aqueous.
Q18Classification, Nomenclature and Preparation · Halogen exchange · hard · trap: a true statement that is not the reason
The Finkelstein equilibrium is driven to the right because
(A) sodium iodide is far more soluble in acetone than the other halides✓ YOUR ANSWER
(B) iodine is a better leaving group than chlorine
(C) sodium chloride and sodium bromide are insoluble in acetone and precipitate outCORRECT
(D) the alkyl iodide distils off as it is formed
The option you chose is a true statement — NaI really is the more soluble. But the question asks what drives the equilibrium to the right, and solubility of the starting salt only lets the reaction begin. What pulls it forward is NaCl and NaBr leaving the solution as a precipitate, so by Le Chatelier the system keeps making more of them. This is the same trap as an assertion–reason question where R is true but does not explain A.
True is not the same as responsible. Ask what is removed, not what dissolves.
Q30Properties and Nucleophilic Substitution · Substitution products · easy · trap: aqueous vs alcoholic KOH
An alkyl halide heated with aqueous KOH gives
(A) an alkene✓ YOUR ANSWER
(B) an alkane
(C) an alcoholCORRECT
(D) an ether
Aqueous KOH gives the alcohol; alcoholic KOH gives the alkene. In water, OH− is heavily solvated, acts as a nucleophile and attacks the carbon. In alcohol, the alkoxide formed is a stronger base, pulls off a β-hydrogen and eliminates. You gave the alcoholic-KOH answer to the aqueous-KOH question.
aq. KOH → alcohol · alc. KOH → alkene
Q42Properties and Nucleophilic Substitution · SN1 and SN2 mechanisms · hard · trap: a dependency reversed
Which of the following statements are correct? A. An SN2 reaction proceeds through a transition state and not through an intermediate. B. An SN1 reaction is favoured by a polar protic solvent. C. Allylic and benzylic halides are unusually reactive in SN1 substitution. D. The rate of an SN1 reaction doubles when the concentration of the nucleophile is doubled.
(A) 1, 3 and 4 only
(B) 1 and 4 only
(C) 2, 3 and 4 only✓ YOUR ANSWER
(D) 1, 2 and 3 onlyCORRECT
Of the four statements you kept 2 and 3, which are right, dropped 1, which is also right, and accepted 4, which is wrong. Statement 1 is true: SN2 passes through a transition state, never an isolable intermediate — it is SN1 that has an intermediate, the carbocation. Statement 4 is false: an SN1 rate is first order in the substrate alone, rate = k[RX]. Doubling the nucleophile does nothing, because the nucleophile is not in the slow step.
Q55Stereochemistry, Elimination and Metals · Reaction with metals · easy · trap: Na vs Mg
An alkyl halide treated with magnesium in dry ether gives
(A) an alkane✓ YOUR ANSWER
(B) an alkyl magnesium halideCORRECT
(C) an alcohol
(D) an alkene
That is the Wurtz answer given to a Grignard question. Two different metals, two different products: Na in dry ether couples two alkyl halides into an alkane; Mg in dry ether inserts itself into the C—X bond and gives the Grignard reagent R—Mg—X. The dry ether is common to both, which is why they get swapped.
Na → alkane (Wurtz) · Mg → RMgX (Grignard)
Q70Haloarenes and Polyhalogen Compounds · Low reactivity of haloarenes · hard · trap: a dependency reversed
Which of the following statements are correct? A. The C—Cl bond in chlorobenzene has partial double bond character. B. A nitro group at the meta position has little effect on the ease of displacement. C. The carbon bonded to chlorine in chlorobenzene is sp2 hybridised. D. Chlorobenzene is more reactive than chloromethane towards aqueous NaOH.
(A) 1 and 4 only
(B) 1, 2 and 3 onlyCORRECT
(C) 1, 3 and 4 only✓ YOUR ANSWER
(D) 2, 3 and 4 only
The same shape of mistake as Q42. You kept 1 and 3, which are right, dropped 2, which is also right, and accepted 4, which is wrong — and wrong in the direction. Chlorobenzene is far less reactive than chloromethane towards aqueous NaOH, because of the partial double bond character you correctly accepted in statement 1. Statement 1 and statement 4 contradict each other, and you ticked both. Statement 2 is true: a nitro group only activates from ortho and para, where its minus-R effect can reach the carbon bearing the chlorine; from meta it has little effect.
Chlorobenzene is less reactive, not more. Nitro helps only from ortho and para.
(D) dichlorodiphenyltrichloroethaneCORRECT — and you ticked it too
You found the right answer. Both ticks are complete and neither is struck out, so on an OMR this reads as two responses and scores −1 instead of +4. That is a five-mark swing on a question you had already solved.
One tick per question. If you change your mind, cross the first one out.
What to do before the next paper
Write the reagent table out from memory, once a day for a week aq. KOH, alc. KOH, NaI/dry acetone, SbF3, Na/dry ether, Mg/dry ether, AgNO2 vs KNO2, KCN vs AgCN. Eight rows. Until it is faster than thinking.
For every multi-statement question, mark each statement T or F in the margin before you look at the options You were 2 out of 4 on the statements in both Q42 and Q70 but scored zero on both, because the options are all-or-nothing. Judging the statements first, on paper, is what converts partial knowledge into marks.
On any statement that contains a comparison, write the arrow “more reactive than”, “rate doubles when”, “faster than” — draw the arrow and ask which end is bigger. Both of your statement errors were direction errors.
One tick per question, and cross out anything you change Q78 was answered correctly and scored as wrong. That is the cheapest mark on this paper to recover.
The eight rows to know cold
Reagent and conditions
What it does
aqueous KOH
OH− acts as a nucleophile → alcohol
alcoholic KOH
alkoxide acts as a base → alkene
NaI in dry acetone
Finkelstein → alkyl iodide
SbF3 or Hg2F2, heat
Swarts → alkyl fluoride
Na in dry ether
Wurtz → alkane, twice the carbons
Mg in dry ether
Grignard → R—Mg—X
KCN (ionic) vs AgCN (covalent)
nitrile R—CN vs isocyanide R—NC
KNO2 (ionic) vs AgNO2 (covalent)
alkyl nitrite R—ONO vs nitroalkane R—NO2
Marked against the printed answer key for this paper. 72 correct, 7 wrong, 1 double-marked, 0 left blank. Strict score 280 / 320; 285 / 320 if the second tick on Q78 is taken as the final answer.