ILTS Test 3 · Chemistry — Practical Chemistry
Error notes · Aamirah Fathima · 80 Q · 320 marks · target 285 (working goal 300) · danger line 260
152
equivalent / 180 (target 150)
1. The blanks cost as much as the errors
Six blanks = 24 marks; five wrong = 25 marks. The target was 14 away. Four of the six blanks (Q13, 21, 33, 48) were circled to return to and never answered — the same pattern as the MBI paper, where Q61 and Q65 were circled and left.
New rule: at the 60-minute mark on an 80-minute paper, stop and clear every circle. A flagged question left blank scores exactly the same as one never read. Guessing between two options is worth +1.5 on average; leaving it is worth 0.
2. One error repeating across three papers
She marks a true Reason as false.
Fix — a fourth step in the A–R routine: 1. A true or false? 2. R true or false? 3. Is R itself a correct NCERT statement, judged alone? 4. Only then, does R explain A? Step 3 is the one she is skipping — she is testing R against A instead of on its own.
3. What went right
- Cation and anion analysis, Q37–Q68: 30 / 32 attempted correct — group reagents, confirmatory tests, brown ring, sodium carbonate extract, all clean.
- Titration block Q69–Q78: 9 / 10, including every numerical (oxalic acid mass, normality, KMnO₄ volumes for both oxalate and Mohr's salt).
- Lassaigne's test and functional groups, Q1–Q12: 12 / 12.
- Five of six match-the-following correct; the statement-count questions Q10, Q26, Q54, Q68 all correct.
- Best ILTS paper of the cycle so far, and the only one above its 180-scale target.
Assertion–Reason
Q17WrongCRejecting a true ReasonFehling's and aromatic aldehydes
A: Benzaldehyde gives a silver mirror with Tollens' but does not reduce Fehling's. R: Fehling's responds to aliphatic aldehydes but not to aromatic aldehydes.
Her answerA is true but R is false
Correct answerBoth true, R is the correct explanation of A
WhyR is a standard NCERT lab fact — Fehling's oxidises aliphatic aldehydes only, which is exactly why benzaldehyde fails it while still reducing Tollens'. So R is true and it explains A.
Where it went wrong · fixShe marked a true Reason as false. Fourth time across three papers (EMI Q26, MBI Q62, and Q75 on this paper). Add a fourth step to the A–R routine: after writing R's verdict, ask 'is R itself correct NCERT?' before judging the link.
Q75WrongCRejecting a true ReasonSelf-indicator in permanganate titration
A: A permanganate titration needs no external indicator. R: The first permanent pink from an excess drop of permanganate marks the end point.
Her answerA is true but R is false
Correct answerBoth true, R is the correct explanation of A
WhyKMnO₄ is its own indicator: the first drop in excess turns the solution permanently pink, and that is the end point. R is true and is the reason A is true.
Where it went wrong · fixSame failure as Q17. She answered Q76 and Q77 (the harder titration-chemistry questions) correctly, so this is not a knowledge gap.
Statement count
Q51WrongNOver-rejectionGroup V confirmatory tests
How many are correct? A: Ca²⁺ — white precipitate with ammonium oxalate. B: Ba²⁺ — apple-green flame. C: Mg²⁺ — white crystalline precipitate with disodium hydrogen phosphate. D: Sr²⁺ — yellow precipitate with potassium chromate.
Her answerOnly two
Correct answerOnly three
WhyA, B and C are all correct. Only D is false: the yellow precipitate with potassium chromate confirms BARIUM, not strontium (strontium gives a white precipitate with ammonium sulphate).
Where it went wrong · fixShe almost certainly doubted C — the magnesium phosphate test is correct. Count the statements you can prove FALSE; everything else stands.
Cation analysis
Q53WrongNNCERT recallAmmonium ion, Group 0
Ammonium ion, the Group 0 cation, is detected by?
Her answerAdding dilute hydrochloric acid, when a white precipitate forms
Correct answerWarming with sodium hydroxide, when a gas that turns red litmus blue is evolved
WhyNH₄⁺ + OH⁻ on warming gives ammonia gas, which turns moist red litmus blue and gives white fumes with a glass rod dipped in HCl. Her option describes the Group I test for Pb²⁺, Ag⁺ and Hg₂²⁺.
Where it went wrong · fixGroup 0 is tested on the ORIGINAL solution before any group reagent. Card: NH₄⁺ → NaOH + warm → ammonia → red litmus turns blue.
Match-the-following
Q79WrongSArrangement / orderIndicators and primary standards
Match: phenolphthalein, methyl orange, potassium permanganate, oxalic acid with their descriptions.
Her answerA–II, B–IV, C–I, D–III
Correct answerA–II, B–IV, C–III, D–I
WhyPhenolphthalein — colourless in acid, pink in alkali (II). Methyl orange — red in acid, yellow in alkali (IV). KMnO₄ — self indicator, permanent pink at the end point (III). Oxalic acid — primary standard (I).
Where it went wrong · fixRows A and B correct, rows C and D swapped — her recurring match fault, and she had eliminated it in the MBI paper (6/6 there). Solve all four rows in the margin before reading the options.
Blank — flagged and never answered
Q13BlankTBlank — flaggedCeric ammonium nitrate
A red colouration with ceric ammonium nitrate indicates?
Her answerLeft blank
Correct answerAn alcoholic group
WhyCeric ammonium nitrate gives a red colour with alcohols (the cerium complex with the –OH group).
Where it went wrong · fixCircled to return to, never answered. Card: CAN red → alcohol · neutral FeCl₃ violet → phenol.
Q21BlankTBlank — flaggedCarbylamine test
A foul smell on warming a compound with chloroform and alcoholic KOH indicates?
Her answerLeft blank
Correct answerA primary amine
WhyThe carbylamine (isocyanide) test: only primary amines, aliphatic or aromatic, give the offensive isocyanide smell. Secondary and tertiary amines do not respond.
Where it went wrong · fixCircled, never answered. Card: CHCl₃ + alc. KOH + foul smell → 1° amine only.
Q33BlankTBlank — flaggedXanthoproteic test
In the xanthoproteic test, the yellow colour turns what on adding ammonia?
Her answerLeft blank
Correct answerOrange
WhyConcentrated HNO₃ nitrates the aromatic rings of the protein to give a yellow colour, which deepens to orange in alkali (ammonia).
Where it went wrong · fixCircled, never answered. Protein card: biuret → violet · xanthoproteic → yellow then orange with ammonia · Millon's → brick red.
Q48BlankTBlank — flaggedDimethylglyoxime
A bright red precipitate with dimethylglyoxime in ammoniacal solution confirms?
Her answerLeft blank
Correct answerNi²⁺
WhyDMG gives the classic rosy-red nickel complex. She used this same fact correctly as a wrong option in Q42 (copper is confirmed by the chocolate-brown ferrocyanide precipitate).
Where it went wrong · fixCircled, never answered — and she had the knowledge two questions earlier. Card: DMG red → Ni²⁺ · K₄[Fe(CN)₆] chocolate-brown → Cu²⁺ · KSCN blood-red → Fe³⁺.
Blank — not attempted
Q28BlankTBlank — not attemptedIodoform positive, 2,4-DNP negative
A compound gives a yellow precipitate with iodine and NaOH but no precipitate with 2,4-DNP. It is most likely?
Her answerLeft blank
Correct answerEthanol
WhyNo 2,4-DNP precipitate means no carbonyl group, so acetaldehyde, acetone and benzaldehyde are all out. Ethanol has the CH₃CH(OH)– group needed for iodoform, but no C=O.
Where it went wrong · fixA two-step elimination question. Rule: 2,4-DNP negative rules out every aldehyde and ketone in one move.
Q37BlankTBlank — not attemptedGroup I reagent
The group reagent for Group I cations is?
Her answerLeft blank
Correct answerDilute hydrochloric acid
WhyGroup I (Pb²⁺, Ag⁺, Hg₂²⁺) precipitates as chlorides with dilute HCl.
Where it went wrong · fixShe answered the Group III, IV and V reagents correctly (Q43, Q46, Q49), so this is a slip, not a gap. The five reagents must be automatic: I dil. HCl · II H₂S in dil. HCl · III NH₄Cl + NH₄OH · IV H₂S in NH₄OH · V (NH₄)₂CO₃ with NH₄Cl/NH₄OH.
Fix list before 4 October
- Clear every flag by the 60-minute mark. This is now worth more than any single topic: 24 marks here, 8 in MBI.
- A–R step 3: judge R alone as an NCERT statement before judging the link.
- Match questions: write all four rows in the margin first — the swap is nearly always in rows C and D.
- Flashcards to add today: CAN red → alcohol · carbylamine → 1° amine only · 2,4-DNP negative rules out all aldehydes and ketones · xanthoproteic yellow → orange with ammonia · Group I reagent = dilute HCl · DMG red → Ni²⁺ · NH₄⁺ → NaOH + warm → red litmus turns blue · KMnO₄ = self indicator, oxalic acid = primary standard.
- Statement counting: count only what you can prove false; do not reject a statement because it feels unfamiliar (Q51, magnesium phosphate).