Maharashtra HSC Chemistry Model Paper 2027 — Full Paper With Solutions

This model paper follows the official MSBSHSE pattern for HSC Chemistry 2027. Theory: 70 marks in 3 hours. Practical: 30 marks separately.

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Paper Structure

Section	Type	Marks
Section A	MCQ — 8 questions	8
Section B	Very Short Answer — 6 questions (2 marks)	12
Section C	Short Answer 1 — 4 questions (3 marks)	12
Section D	Short Answer 2 — 4 questions (4 marks)	16
Section E	Long Answer — 1 question (5 marks)	... wait

Let me use the correct MSBSHSE format:

Section	Type	Marks
Section A	MCQ	8
Section B	Very Short Answer (2 marks × 6)	12
Section C	Short Answer (3 marks × 4)	12
Section D	Short Answer (4 marks × 4)	16
Section E	Long Answer (5 marks × 4, attempt 3)	15
Practical	Lab Assessment	30

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SECTION A — MCQ (1 Mark Each)

Q1. Which of the following solutions has the highest boiling point?

(a) 1M glucose (b) 1M NaCl (c) 1M CaCl₂ (d) 1M AlCl₃

Answer: (d) 1M AlCl₃
(AlCl₃ → Al³⁺ + 3Cl⁻ = 4 particles; highest van't Hoff factor i=4; ΔTb = iKbm)

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Q2. Kohlrausch's Law is related to:

(a) Osmotic pressure (b) Molar conductivity at infinite dilution
(c) Rate of reaction (d) Electrode potential

Answer: (b) Molar conductivity at infinite dilution

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Q3. For a first order reaction, the half-life is:

(a) Directly proportional to initial concentration
(b) Inversely proportional to initial concentration
(c) Independent of initial concentration
(d) Proportional to rate constant

Answer: (c) Independent of initial concentration
(t₁/₂ = 0.693/k for first order — independent of concentration)

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Q4. The IUPAC name of [Co(NH₃)₆]³⁺ is:

(a) Hexamminecobalt(III) ion (b) Cobalt hexammine
(c) Hexacobaltammine (d) Tricobalthexammine

Answer: (a) Hexamminecobalt(III) ion

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Q5. Which of the following is an example of an addition polymer?

(a) Nylon-6,6 (b) Polyethylene (c) Bakelite (d) Terylene

Answer: (b) Polyethylene
(Formed by addition polymerisation of ethylene: nCH₂=CH₂ → (−CH₂−CH₂−)n)

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Q6. Lucas test is used to distinguish between:

(a) Primary and secondary alcohols only
(b) Primary, secondary and tertiary alcohols
(c) Aldehydes and ketones
(d) Alcohols and phenols

Answer: (b) Primary, secondary and tertiary alcohols

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Q7. The basicity of amines follows the order:

(a) 3° > 2° > 1° > NH₃ in gas phase
(b) 1° > 2° > 3° in aqueous solution
(c) NH₃ > 1° > 2° > 3°
(d) All have equal basicity

Answer: (a) 3° > 2° > 1° > NH₃ in gas phase

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Q8. Which biomolecule is the genetic material in most organisms?

(a) RNA (b) Protein (c) DNA (d) Lipid

Answer: (c) DNA

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SECTION B — Very Short Answer (2 Marks Each)

Q9. State Henry's Law. Write its mathematical expression.

Answer: Henry's Law states that at constant temperature, the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the solution.

Mathematical form: p = K_H × x
where p = partial pressure of gas, K_H = Henry's constant, x = mole fraction of gas in solution.

Applications: Carbonated drinks (CO₂ under high pressure), oxygen cylinders for deep sea divers.

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Q10. Define rate constant. How does temperature affect it?

Answer: The rate constant (k) is the proportionality constant in the rate law equation.
Rate = k[A]^m[B]^n
At a given temperature, k is constant for a specific reaction.

Effect of temperature: Rate constant increases with temperature.
Arrhenius equation: k = Ae^(−Ea/RT)
A = frequency factor, Ea = activation energy, R = gas constant, T = temperature
A 10°C rise approximately doubles the rate constant for most reactions.

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Q11. What are chelate compounds? Give one example.

Answer: Chelate compounds are coordination compounds in which a polydentate ligand (chelating agent) forms a ring structure by donating two or more lone pairs to the central metal ion.

Example: [Cu(en)₂]²⁺ — Bis(ethylenediamine)copper(II) ion
Here ethylenediamine (en = H₂N−CH₂−CH₂−NH₂) is a bidentate ligand that forms a 5-membered chelate ring.

Chelate compounds are more stable than similar non-chelate compounds (chelate effect).

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Q12. Write the mechanism for the preparation of ethanol from ethene.

Answer: Hydration of Ethene (Industrial method):

CH₂=CH₂ + H₂O → CH₃CH₂OH
Conditions: H₃PO₄ catalyst, 300°C, 70 atm pressure

Mechanism (acid catalysed):

1. Protonation of ethene: CH₂=CH₂ + H⁺ → CH₃CH₂⁺ (carbocation)
2. Nucleophilic attack of water: CH₃CH₂⁺ + H₂O → CH₃CH₂OH₂⁺
3. Deprotonation: CH₃CH₂OH₂⁺ → CH₃CH₂OH + H⁺

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SECTION C — Short Answer (3 Marks Each)

Q13. Explain electrochemical series and its applications.

Answer: The electrochemical series (activity series) is the arrangement of metals and non-metals in order of their standard reduction potentials (E°) from most negative to most positive.

Metal	E° (V)
Li	−3.05
Na	−2.71
Mg	−2.37
Zn	−0.76
Fe	−0.44
H₂	0.00
Cu	+0.34
Ag	+0.80
Au	+1.50

Applications:

1. Predicting whether a metal displaces another from its salt solution (higher activity displaces lower)
2. Predicting spontaneity of cell reaction (positive EMF = spontaneous)
3. Choosing electrode materials for galvanic cells
4. Predicting metal corrosion tendency

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Q14. Distinguish between SN1 and SN2 reactions. Which substrates favour each?

Answer:

Feature	SN1	SN2
Steps	Two (carbocation intermediate)	One (concerted)
Rate	Depends on [substrate] only	Depends on [substrate] and [nucleophile]
Stereochemistry	Racemisation	Inversion (Walden inversion)
Favoured by	Tertiary substrates, polar protic solvents	Primary substrates, strong nucleophile, polar aprotic solvents

Example SN1: (CH₃)₃CBr + H₂O → (CH₃)₃COH
Example SN2: CH₃Br + OH⁻ → CH₃OH + Br⁻

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SECTION D — Short Answer (4 Marks Each)

Q15. Explain the preparation, properties and uses of p-Block element compound: Sulphuric Acid (H₂SO₄).

Answer:

Preparation — Contact Process:

1. Burning sulphur: S + O₂ → SO₂
2. Catalytic oxidation: 2SO₂ + O₂ ⇌ 2SO₃ (V₂O₅ catalyst, 450°C, 1–2 atm)
3. Absorption: SO₃ + H₂SO₄ → H₂S₂O₇ (oleum)
4. Dilution: H₂S₂O₇ + H₂O → 2H₂SO₄

Properties:

• Colourless, oily, dense liquid (density 1.84 g/mL)
• Dehydrating agent: Removes water from organic compounds; chars sugar, paper
• Oxidising agent: Oxidises metals and non-metals (conc. H₂SO₄)
• Acidic properties: Strong diprotic acid, highly corrosive

Uses:

1. Manufacture of fertilisers (superphosphate of lime)
2. Storage batteries (lead-acid batteries)
3. Manufacture of explosives (TNT, nitroglycerine)
4. Petroleum refining and metallurgical processes

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SECTION E — Long Answer (5 Marks Each — Attempt 3 of 4)

Q16. Explain the mechanism of nucleophilic addition to carbonyl compounds with reference to the reaction of HCN with acetaldehyde.

Answer:

Nucleophilic Addition to Carbonyl Compounds:

The C=O group is polar due to the electronegativity difference between C and O. The carbon is electrophilic (δ+) and oxygen is nucleophilic (δ−).

Reaction: CH₃CHO + HCN → CH₃CH(OH)CN (Acetaldehyde cyanohydrin)

Mechanism:

Step 1 — Nucleophilic attack:
The cyanide ion (CN⁻) acts as nucleophile and attacks the electrophilic carbonyl carbon.
CH₃CHO + CN⁻ → CH₃CH(O⁻)(CN) (alkoxide ion intermediate)

Step 2 — Protonation:
The alkoxide ion accepts a proton from HCN.
CH₃CH(O⁻)(CN) + HCN → CH₃CH(OH)(CN) + CN⁻

Product: Acetaldehyde cyanohydrin — CH₃CH(OH)CN

Importance: Cyanohydrins are important synthetic intermediates:

• Hydrolysis gives α-hydroxy acids
• The CN group can be converted to COOH or CH₂NH₂

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Practice Problems (Self Test)

1. Calculate the freezing point depression when 9g of glucose is dissolved in 250g of water. (Kf = 1.86 K kg/mol)
2. Write the IUPAC name and draw the structure of [Fe(CN)₆]³⁻.
3. Distinguish between natural and synthetic polymers with two examples each.
4. Write the reaction of primary amine with HNO₂ (nitrous acid).

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Chapter-Wise Weightage

Chapter	Marks
Solutions	8
Electrochemistry	8
Chemical Kinetics	7
p-Block Elements	8
d and f Block + Coordination	10
Organic Chemistry (Haloalkanes, Alcohols, Carbonyl)	15
Amines	5
Biomolecules and Polymers	9

Tip: Maharashtra HSC Chemistry Section D (4 marks each) and Section E (5 marks each) together carry 31 marks. These require complete, structured answers with equations. Always write the chemical equation first, then explain — you get partial marks even if the explanation is incomplete.