JEE/NEET CHEMISTRY — 50 MARKS -SET 1

JEE/NEET CHEMISTRY — 50 MARKS

Time: 60 Minutes
Maximum Marks: 50

SECTION A — MCQs

20 × 1 = 20 marks

1. Which of the following is the correct order of acidic strength in aqueous medium?
A. H₂O > CH₃OH > NH₃
B. CH₃OH > H₂O > NH₃
C. NH₃ > H₂O > CH₃OH
D. H₂O > NH₃ > CH₃OH

2. The noble gas configuration of phosphorus (Z = 15) is:
A. [Ne] 3s² 3p³
B. [He] 2s² 2p⁶ 3s² 3p³
C. [Ar] 3s² 3p³
D. [Ne] 3s² 3p⁵

3. An element having electronic configuration [Ne] 3s² 3p⁵ belongs to:
A. Group 15, Period 3
B. Group 17, Period 3
C. Group 17, Period 2
D. Group 7, Period 3

4. Which group shows the strongest +R effect?
A. –NO₂
B. –COOH
C. –NH₂
D. –CN

5. The reagents used in the Gattermann–Koch reaction are:
A. CO + HCl/AlCl₃, CuCl
B. CO₂ + HCl/AlCl₃
C. CO + Cl₂/FeCl₃
D. HCN + HCl/AlCl₃

6. Which ligand is strongest according to the spectrochemical series?
A. Cl⁻
B. F⁻
C. NH₃
D. CN⁻

7. Reimer–Tiemann reaction of phenol with CHCl₃/NaOH gives mainly:
A. Benzaldehyde
B. Salicylaldehyde
C. Benzoic acid
D. Toluene

8. The major product of Kolbe’s reaction of sodium phenoxide followed by acidification is:
A. Benzoic acid
B. Salicylic acid
C. Phenol
D. Benzaldehyde

9. A secondary amine reacts with nitrous acid to form:
A. Nitroalkane
B. N-nitrosoamine
C. Alcohol
D. Alkene

10. The equivalent weight of H₂SO₄ in an acid-base reaction is:
A. 98
B. 49
C. 24.5
D. 196

11. For a hydrogen-like atom, the energy of an electron in orbit n is proportional to:
A. n²
B. 1/n
C. –1/n²
D. –n²

12. The correct order of dipole moment is:
A. HF > HCl > HBr > HI
B. HI > HBr > HCl > HF
C. HCl > HF > HBr > HI
D. HF > HI > HBr > HCl

13. A reaction in which two species undergo oxidation-state changes to produce a species having an intermediate oxidation state is called:
A. Disproportionation
B. Comproportionation
C. Neutralisation
D. Hydrolysis

14. Which pair represents structural isomers?
A. cis-2-butene and trans-2-butene
B. n-butane and isobutane
C. (R)-2-butanol and (S)-2-butanol
D. cis-2-butene and 2-butene

15. Which alkane conformation is the most stable?
A. Eclipsed
B. Fully eclipsed
C. Staggered
D. Partially eclipsed

16. Ozonolysis of propene followed by reductive work-up gives:
A. Methanal + ethanal
B. Methanal + methanol
C. Ethanal + ethanol
D. Acetone + methanal

17. Which statement is correct for an SN2 reaction?
A. It proceeds through carbocation formation
B. Rate depends only on substrate concentration
C. It involves backside attack
D. It is favoured by tertiary alkyl halides

18. Acid chlorides react with water to produce:
A. Alcohol
B. Aldehyde
C. Carboxylic acid
D. Ether

19. Hydration of a terminal alkyne in the presence of HgSO₄/H₂SO₄ ultimately gives:
A. Primary alcohol
B. Aldehyde
C. Ketone
D. Ether

20. The reaction of an alkene with cold, dilute alkaline KMnO₄ is commonly used as:
A. Baeyer test
B. Tollens’ test
C. Fehling’s test
D. Lucas test

SECTION B — STATEMENT / CONCEPT

10 × 2 = 20 marks

21. Consider the following statements about SN1 and SN2 reactions:

  1. SN1 reactions involve carbocation formation.
  2. SN2 reactions proceed through a single-step mechanism.
  3. SN1 is generally favoured by tertiary substrates.
  4. SN2 reactions show retention of configuration.

Which statements are correct?
A. 1, 2 and 3 only
B. 1 and 4 only
C. 2 and 3 only
D. All four

22. For a zero-order reaction, the time required for complete consumption of reactant is finite, whereas for a first-order reaction, complete consumption theoretically requires infinite time.

If the half-life of a first-order reaction is 20 min, the time required for 75% completion is:

A. 20 min
B. 30 min
C. 40 min
D. 60 min

23. HBr adds to propene in the presence of peroxide.

Answer the following:

(i) State the major product.
(ii) Name the rule responsible for this orientation.
(iii) Why does this reaction proceed through a radical mechanism?

24. Match the following:

ReactionProduct/feature
A. Clemmensen reduction1. Zn(Hg)/HCl
B. Wolff–Kishner reduction2. NH₂NH₂/KOH
C. Cannizzaro reaction3. Aldehydes without α-H
D. Aldol reaction4. Aldehydes/ketones having α-H

Choose the correct matching.

25. Give the products obtained in the following tests:

(i) Alkene + Br₂/CCl₄
(ii) Terminal alkyne + ammoniacal AgNO₃
(iii) Alkene + cold alkaline KMnO₄

26. A Grignard reagent reacts with a nitrile followed by hydrolysis.

(i) Write the general reaction.
(ii) What class of compound is obtained?
(iii) What happens to the nitrile carbon?

27. Complete the following reactions:

(i) CH₃CH₂Br + alc. KOH → ?
(ii) CH₃CH₂Br + aq. KOH → ?
(iii) CH₃CH₂OH —conc. H₂SO₄, 443 K→ ?

28. Complete the following reactions:

(i) 2CH₃CHO + dilute NaOH → ?
(ii) 2C₆H₅CHO + concentrated NaOH → ?

Name both reactions.

29. An ideal gas expands from V₁ to V₂.

Write the expression for work done when expansion is:

(i) Reversible and isothermal
(ii) Against constant external pressure

30. Define the following:

(i) Heat capacity
(ii) Specific heat capacity
(iii) Molar heat capacity

Also write the relationship between heat supplied and temperature change.

SECTION C — NUMERICAL / JEE-LEVEL

5 × 2 = 10 marks

31. The enthalpy change of a reaction at constant pressure is –50 kJ mol⁻¹. If the reaction involves gaseous reactants and products, explain why ΔH and ΔU may differ. Write the relation between ΔH and ΔU for gaseous reactions.

32. Calculate the heat required to raise the temperature of 200 g of water from 25°C to 75°C, given:

Specific heat of water = 4.2 J g⁻¹ K⁻¹.

33. The enthalpy of neutralisation of a strong acid by a strong base is approximately:

A. +57.1 kJ mol⁻¹
B. –57.1 kJ mol⁻¹
C. –5.71 kJ mol⁻¹
D. +5.71 kJ mol⁻¹

Explain the reason for its nearly constant value.

34. Using Hess’s law:

C + ½O₂ → CO  ΔH = –110.5 kJ mol⁻¹
CO + ½O₂ → CO₂ ΔH = –283.0 kJ mol⁻¹

Calculate ΔH for:

C + O₂ → CO₂

35. For the reaction:

N₂(g) + 3H₂(g) → 2NH₃(g)

Predict the sign of ΔS and explain your answer.

BONUS JEE/NEET REACTION REVISION

Before attempting the paper, revise these high-yield reaction pairs:

  • Reimer–Tiemann: Phenol → salicylaldehyde
  • Kolbe–Schmitt: Phenol → salicylic acid
  • Gattermann–Koch: Benzene → benzaldehyde
  • Clemmensen: C=O → CH₂ using Zn(Hg)/HCl
  • Wolff–Kishner: C=O → CH₂ using NH₂NH₂/KOH
  • Cannizzaro: Aldehyde without α-H → alcohol + carboxylate
  • Aldol: Carbonyl compound with α-H → β-hydroxy carbonyl compound
  • Ozonolysis: Alkene → carbonyl compounds
  • Baeyer test: Alkene/alkyne decolourises alkaline KMnO₄
  • Ammoniacal AgNO₃: Terminal alkyne gives silver acetylide
  • Br₂/CCl₄: Unsaturation test
  • Grignard + nitrile: → ketone after hydrolysis
  • Nitrile hydrolysis: → carboxylic acid under complete hydrolysis

ans of all only ans

ANSWER KEY — 50 MARKS

  1. B
  2. A
  3. B
  4. C
  5. A
  6. D
  7. B
  8. B
  9. B
  10. B
  11. C
  12. A
  13. B
  14. B
  15. C
  16. A
  17. C
  18. C
  19. C
  20. A
  21. A
  22. C
  23. 1-bromopropane; Anti-Markovnikov rule; free-radical mechanism
  24. A–1, B–2, C–3, D–4
  25. (i) Vicinal dibromoalkane (ii) Silver acetylide precipitate (iii) Vicinal diol
  26. RMgX + R′CN → R′C(=N MgX)R →[H₃O⁺] R′COR; ketone; nitrile carbon becomes carbonyl carbon
  27. (i) CH₂=CH₂ (ii) CH₃CH₂OH (iii) CH₂=CH₂
  28. (i) 3-hydroxybutanal (aldol) (ii) C₆H₅CH₂OH + C₆H₅COONa (Cannizzaro)
  29. (i) w = −nRT ln(V₂/V₁) (ii) w = −Pext(V₂−V₁)
  30. Heat capacity = q/ΔT; Specific heat = q/(mΔT); Molar heat capacity = q/(nΔT)
  31. ΔH = ΔU + Δn(g)RT
  32. 42,000 J = 42 kJ
  33. B
  34. −393.5 kJ mol⁻¹
  35. ΔS < 0

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