St.

Xavier's Senior Secondary School

Ramnagar, Ambedkar Nagar

PRE-BOARD EXAMINATION 2024-2025 ( 2ND )

Class 12 - Chemistry
Time Allowed: 3 hours Maximum Marks: 70

General Instructions:

Read the following instructions carefully.

1. There are 33 questions in this question paper with internal choice.

2. SECTION A consists of 16 multiple-choice questions carrying 1 mark each.

3. SECTION B consists of 5 very short answer questions carrying 2 marks each.

4. SECTION C consists of 7 short answer questions carrying 3 marks each.

5. SECTION D consists of 2 case-based questions carrying 4 marks each.

6. SECTION E consists of 3 long answer questions carrying 5 marks each.

7. All questions are compulsory.

8. Use of log tables and calculators is not allowed.

Section A
1. Vinylic halides contain: [1]

a) a sp3-hybridized carbon atom, next to an b) a halogen atom bonded to an sp2-hybridized

aromatic ring, to which halogen atom is carbon atom of a carbon-carbon double

bonded. bond.

c) a halogen atom bonded to an sp3-hybridized d) a sp2-hybridized carbon atom of an aromatic

carbon atom next to carbon-carbon double ring which is bonded to a halogen.
bond.
2. Which of the following structures represents α-D-glucose? [1]

a) b)

c) d)

3. IUPAC name of the following compound is C H 3 − C H − OC H3 is ________. [1]

|

C H3

a) 2 – methoxy – 2 – methylethane b) 2 – methoxypropane

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 c) isopropylmethyl ether d) 1 – methoxy – 1 – methylethane
4. Compound 'A' undergoes the formation of cyanohydrins which on hydrolysis gives lactic acid [1]
(CH3CHOHCOOH). Therefore, compound 'A' is:

a) Acetone b) Benzaldehyde

c) Acetaldehyde d) Formaldehyde
5. The ionic reactions are generally very fast because [1]

a) It does not involve bond breaking b) The number of collisions between ions are
very large

c) Reactions are highly exothermic d) The energy of interaction between charged

ion is greater than between neutral
molecules
6. Match the items of column I with appropriate entries of column II. [1]

Column I Column II

(a) Non ideal solution with positive deviation (i) H2O (57%) + HI (43%)

(b) Maximum boiling azeotrope (ii) CHCl3 + (CH3)2CO

(c) Non ideal solution with negative deviation (iii) C2H5OH (95.4%) + H2O (4.6%)

(d) Minimum boiling azeotrope (iv) CCl4 + C6H5CH3

a) (a) - (iv), (b) - (i), (c) - (ii), (d) - (iii) b) (a) - (iv), (b) - (iii), (c) - (ii), (d) - (i)

c) (a) - (i), (b) - (ii), (c) - (iii), (d) - (iv) d) (a) - (ii), (b) - (iii), (c) - (i), (d) - (iv)
O

||
O

||
[1]
7. The IUPAC name of CH 3 − C − CH2 − C − H is:

a) 1-oxobutanal b) 3-oxobutanal

c) 1-oxobutanal-3-one d) 3-oxobutanone
8. The most common and stable oxidation state of a Lanthanoid is: [1]

a) +3 b) +4

c) +6 d) +2
9. As temperature increases, the reaction rate: [1]

a) First decreases then increases b) Increases

c) Decreases d) Stays the same

10. Which of the following is the strongest acid? [1]

a) Methyl alcohol b) Acetic acid

c) Phenol d) Water
11. Lucas reagent is? [1]

a) anhydrous PdCl2 and conc.HCl. b) anhydrous AlCl3 and conc.HCl.

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 c) anhydrous CaC2 and conc. HCl. d) anhydrous ZnCl2 and conc. HCl.

12. The source of nitrogen in Gabriel synthesis of amines is ________. [1]

a) Sodium nitrite, NaNO2 b) Potassium cyanide, KCN

c) Potassium phthalimide, C H (CO) N-K+ d) Sodium azide, NaN3

6 4 2

13. Assertion (A): β-pleated sheet structure of protein shows maximum extension. [1]
Reason (R): Intermolecular hydrogen bonding is present in them.

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

14. Assertion (A): α-Hydrogen atoms in aldehydes and ketones are acidic. [1]
Reason (R): The anion left after the removal of α-hydrogen is stabilised by inductive effect.

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

15. Assertion (A): Boiling point of alkyl halides increases with an increase in molecular weight. [1]
Reason (R): Boiling point of alkyl halides is in the order RI > RB > RCl > RF.

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

16. Assertion (A): Absolute ethanol can be obtained by simple fractional distillation of a mixture of alcohol and [1]
water.

Reason (R): The absolute alcohol boils at 78.3oC.

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

Section B
17. Using IUPAC norms, write the formulae for the following: [2]
i. Potassium trioxalatoaluminate (Ill)
ii. Dichlorido bis(ethane-1, 2-diamine) cobalt(Ill) ion
18. Account for the following: The second and third series members in each group of the transition elements have [2]
very similar atomic radii.
19. Answer the following: [2]
(a) Identify the reaction order if the unit of rate constant is sec-1. [1]
(b) a. In a reaction, if the concentration of reactant X is tripled, the rate of reaction becomes twenty- [1]
seven times. What is the order of the reaction?
b. State a condition under which a bimolecular reaction is kinetically a first-order reaction. Give an
example of such a reaction.

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20. Visha took two aqueous solutions — one containing 7·5 g of urea (Molar mass = 60 g/mol) and the other [2]
containing 42.75 g of substance Z in 100 g of water, respectively. It was observed that both the solutions froze at
the same temperature. Calculate the molar mass of Z.
OR
Why is liquid ammonia bottle first cooled in ice before opening it?
21. i. (CH3)3C - CHO does not undergo aldol condensation. Why? [2]

ii. Distinguish between Acetophenone and Benzophenone with the help of a chemical test.
Section C
22. In the button cell, widely used in watches, the following reaction takes place [3]
Zn (s) + Ag2 O (s) + H2 O (l) → Zn
2+
(aq) + 2Ag (s) + 20H
−
(aq) Given that
Θ Θ
E +
= 0.80V , E 2+
= −0.76 V
(Ag /Ag) (Zn /Zn)

Calculate standard emf and standard free Gibbs energy of the cell.
23. Consider the reaction: [3]
2A + B → C + D
Following results were obtained in experiments designed to study the rate of reaction:

Exp. No. Initial concentration (mol L-1 ) [A] [B] Initial rate of formation [D] (m/min)

1. 0.10 0.10 1.5 × 10

−3

2. 0.20 0.20 3.0 × 10

−3

3. 0.20 0.40 6.0 × 10

−3

i. Write the rate law for the reaction.

ii. Calculate the value of rate constant for the reaction.
iii. Which of the following possible reaction mechanism is consistent with the rate law?
I. A + B → C + E (slow)

A + E → D (fast)

II. B → C + E (slow)
A + E → F (fast)

A + F → D (fast)

24. Draw the structure and name the product formed if the following alcohols are oxidized. Assume that an excess [3]
of oxidizing agent is used.
i. CH3CH2CH2CH2OH

ii. 2-Butanol
iii. 2-methylpropanol
OR
Give equations of the following reactions:
i. Oxidation of propan-1-ol with alkaline KMnO4 solution.

ii. Bromine in CS2 with phenol.

iii. Dilute HNO3 with phenol.

iv. Treating phenol with chloroform in presence of aqueous NaOH.
25. Write the equations involved in the following reactions: [3]

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 i. Cannizzaro reaction
ii. Aldol condensation
iii. Hell-Volhard-Zelinsky reaction
26. When a certain conductance cell was filled with 0.1 M KCl, it has a resistance of 85 ohms at 25°C. When the [3]
same cell was filled with an aqueous solution of 0.052 M unknown electrolyte, the resistance was 96 ohms.
Calculate the molar conductance of the electrolyte at this concentration.
[Specific conductance of 0.1 M KCl = 1.29x 10-2 ohm" cm"]
27. An organic compound A on heating with NH3 and cuprous oxide at high pressure gives compound B. The [3]

compound B on treatment with ice-cold solution of NaNO2 and HCl gives C, which on heating with copper
turning and HCl gives A again. Identify A, B & C. compound.
28. Explain why electrolysis of aqueous solution of NaCl gives H2 at cathode and Cl2 at anode. Write overall [3]
reaction.
0 0
E +
= −2.71V ; E = −0.83V
Na /Na H2 O/H2
( )
0 0
E −
= +1.36V ; E +
= 1.23V
C l2 /2C l H +O2 /H2 O

Section D
29. Read the following text carefully and answer the questions that follow: [4]
The d-block of the periodic table contains the elements of the groups 3 to 12 and are known as transition

elements. In general, the electronic configuration of these elements is (n - 1)d1-10 ns1-2. The d-orbitals of the
penultimate energy level in their atoms receive electrons giving rise to the three rows of the transition metals i.e.
3d, 4d and 5d series. However, Zn, Cd and Hg are not regarded as transition elements. Transition elements
exhibit certain characteristic properties like variable oxidation stables, complex formation, formation of coloured
ions, alloys, catalytic activity etc. Transition metals are hard (except Zn, Cd and Hg) and have a high melting
point.
i. Why are Zn, Cd and Hg non-transition elements? (1)
ii. Which transition metal of 3d series does not show variable oxidation state? (1)
iii. Why do transition metals and their compounds show catalytic activity? (2)
OR
Why are melting points of transition metals high? (2)
30. Read the following text carefully and answer the questions that follow: [4]
Raoult's law for volatile liquids states that the partial vapour pressure of each component in the solution is
directly proportional to its mole fraction, whereas for a non-volatile solute, it states that the vapour pressure of a
solution of a non-volatile solute is equal to the vapour pressure of the pure solvent at that temperature multiplied
by its mole fraction. Two liquids A and B are mixed with each other to form a solution, the vapour phase
consists of both components of the solution. Once the components in the solution have reached equilibrium, the
total vapour pressure of the solution can be determined by combining Raoult's law with Dalton's law of partial
pressures. If a non-volatile solute B is dissolved into a solvent A to form a solution, the vapour pressure of the
solution will be lower than that of the pure solvent. The solutions which obey Raoult's law over the entire range
of concentration are ideal solutions, whereas the solutions for which vapour pressure is either higher or lower
than that predicted by Raoult's law are called non-ideal solutions. Non-ideal solutions are identified by
determining the strength of the intermolecular forces between the different molecules in that particular solution.

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 They can either show positive or negative deviation from Raoult's law depending on whether the A - B
interactions in solution are stronger or weaker than A - A and B - B interactions.
i. 20 mL of a liquid A was mixed with 20 mL of liquid B. The volume of resulting solution was found to be
less than 40 mL. What do you conclude from the above data? (1)
ii. Which of the following show positive deviation from Raoult's law? Carbon disulphide and Acetone; Phenol
and Aniline; Ethanol and Acetone. (1)
iii. The vapour pressure of a solution of glucose in water is 750 mm Hg at 100oC. Calculate the mole fraction of
solute. (2)
(Vapour pressure of water at 373 K = 760 mm Hg)
OR
The boiling point of solution increases when 1 mol of NaCl is added to 1 litre of water while addition of 1
mol of methanol to one litre of water decreases its boiling point. Explain the above observations. (2)
Section E
31. Attempt any five of the following: [5]
(a) Which of the two components of starch is water soluble? [1]
(b) i. Why do amino acids show amphoteric behaviour? [1]
ii. What happens when D-Glucose is treated with hydroxylamine?
(c) Give the reaction of glucose with acetic anhydride. Presence of which group is confirmed by this [1]
reaction?
(d) Write the full forms of DNA and RNA. [1]
(e) Write the products obtained after hydrolysis of lactose. [1]
(f) What are nucleic acids? Why two strands in DNA are not identical but are complementary? [1]
(g) Differentiate between [1]
a. Nucleotide and Nucleoside
b. Amylose and Amylopectin

32. [Fe(H2O)6]3+ is strongly paramagnetic whereas [Fe(CN)6]3+ is weakly paramagnetic. Explain. [5]

OR
Using valence bond approach, explain the shape and magnetic behaviour of [Ni(NH3)6]2+.

33. i. Write the structures of main products when benzene diazonium chloride (C +
6 H5 N2
−
Cl ) reacts with the [5]
following reagents :
a. HBF4/Δ
b. Cu /HBr
ii. Write the structures of A, B and C in the following reactions :
Sn/H C l NaN O2 + H C l H2 O

a. C6H5NO2 −−−−→ A −−−−−−−−→ B −−→ C

273K Δ
KC N LiAlH4 H NO2

b. CH3Cl −−−→ A −−−−→ B −−−−→ C

273K

OR
Give reasons:
i. Aniline does not undergo Friedal-Crafts reaction.
ii. Aromatic primary amines cannot be prepared by Gabriel’s phthalimide synthesis.

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iii. Aliphatic amines are stronger bases than ammonia.

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