Class 12 Chemistry — CBSE Board Sample Paper

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Class 12 Chemistry — CBSE Board Sample Paper — solved practice questions

8 Class 12 Board Sample Papers (CBSE) questions with step-by-step solutions. Attempt each, then reveal the answer.

1. Q1hard

   Ammonolysis of ethyl chloride followed by reaction of the amine so formed with 1 mole of methyl chloride gives an amine that

   • Areacts with Hinsberg reagent to form a product soluble in an alkali.
   • Bon reaction with Nitrous acid, produced nitrogen gas.
   • Creacts with Benzenesulphonyl chloride to form a product that is insoluble in alkali.
   • Ddoes not react with Hinsberg reagent.
   Show answer & solution

   Correct answer: (C) reacts with Benzenesulphonyl chloride to form a product that is insoluble in alkali.

   Ammonolysis of ethyl chloride gives ethylamine (a primary amine); reaction with 1 mole of methyl chloride converts it to a secondary amine (N-methylethylamine). A secondary amine reacts with Benzenesulphonyl chloride (Hinsberg reagent) to form a product that is insoluble in alkali.

2. Q2medium

   Which one of the following has the highest dipole moment?

   • ACH3F
   • BCH3Cl
   • CCH3I
   • DCH3Br
   Show answer & solution

   Correct answer: (B) CH3Cl

   The order is CH3I < CH3Br < CH3F < CH3Cl. Although F is the most electronegative, the C-F bond length is small compared to C-Cl. Since dipole moment is the product of charge and bond length, CH3Cl has the highest dipole moment.

3. Q3medium

   Match the properties given in column I with the metals in column II. Column I: (i) Actinoid having configuration [Rn] 5f7 6d1 7s2 (ii) Lanthanoid which has 4f14 electronic configuration in +3 oxidation state (iii) Lanthanoid which shows +4 oxidation state ; Column II: (A) Ce (B) Lu (C) Cm

   • A(i)-(C), (ii)-(B), (iii)-(A)
   • B(i)-(C), (ii)-(A), (iii)-(B)
   • C(i)-(A), (ii)-(B), (iii)-(C)
   • D(i)-(B), (ii)-(A), (iii)-(C)
   Show answer & solution

   Correct answer: (A) (i)-(C), (ii)-(B), (iii)-(A)

   Cm (Curium) has the configuration [Rn]5f7 6d1 7s2; Lu (Lutetium) has 4f14 in its +3 state; Ce (Cerium) shows the +4 oxidation state. Thus (i)-(C), (ii)-(B), (iii)-(A).

4. Q4medium

   Which of the following haloalkanes has the highest boiling point?

   • A2-Bromo-2-methylpropane
   • B2-Bromobutane
   • CBromomethane
   • D1-Bromobutane
   Show answer & solution

   Correct answer: (D) 1-Bromobutane

   Among these bromoalkanes, 1-Bromobutane is a straight-chain isomer with the largest surface area for van der Waals interactions, giving it the highest boiling point.

5. Q5medium

   The initial concentration of R in the reaction R → P is 4.62 x 10-2 mol/L. What is the half life for the reaction if k = 2.31 x 10-2 molL-1s-1?

   • A30 s
   • B3 s
   • C1 s
   • D10 s
   Show answer & solution

   Correct answer: (C) 1 s

   The unit of k (molL-1s-1) indicates a zero order reaction. Half life = [R]o / 2k = (4.62 x 10-2) / (2 x 2.31 x 10-2) = 1 s.

6. Q6medium

   When C6H5COOCOCH3 is treated with H2O, the product obtained is:

   • ABenzoic acid and ethanol
   • BBenzoic acid and ethanoic acid
   • CAcetic Acid and phenol
   • DBenzoic anhydride and methanol
   Show answer & solution

   Correct answer: (B) Benzoic acid and ethanoic acid

   The mixed anhydride C6H5COOCOCH3 on hydrolysis with water gives the two corresponding carboxylic acids: benzoic acid (C6H5COOH) and ethanoic acid (CH3COOH).

7. Q7hard

   'X' and 'Y' in the given table (complex and its ratio of ions in solution) are:

   • AX=[Co(NH3)6]2+ 3Cl-, Y= 1:3
   • BX=[Co(NH3)4Cl2]+Cl-, Y= 1:3
   • CX=[Co(NH3)4Cl2]+Cl-, Y= 1:1
   • DX=[Co(NH3)4Cl2]3+ 3Cl-, Y= 1:1
   Show answer & solution

   Correct answer: (B) X=[Co(NH3)4Cl2]+Cl-, Y= 1:3

   The complex [Co(NH3)4Cl2]+Cl- ionises to give one complex cation and one chloride ion, giving X=[Co(NH3)4Cl2]+Cl- with a ratio Y = 1:3 (as required by the tabulated data).

8. Q8medium

   Which of the following contains only β-D-glucose as its monosaccharide unit:

   • ASucrose
   • BCellulose
   • CStarch
   • DMaltose
   Show answer & solution

   Correct answer: (B) Cellulose

   Cellulose is a polymer of β-D-glucose. Starch contains only α-glucose, sucrose contains α-D-glucose and β-D-fructose, and maltose contains α-D-glucose.

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