Subject: Chemistry
Class XII
Time Allowed: 3 hours
Max. Marks: 70
General Instructions:
Read the following instructions carefully.
a. There are 35 questions in this question paper with internal choice.
b. SECTION A consists of 18 multiple-choice questions carrying 1 mark each.
c. SECTION B consists of 7 very short answer questions carrying 2 marks each.
d. SECTION C consists of 5 short answer questions carrying 3 marks each.
e. SECTION D consists of 2 case- based questions carrying 4 marks each.
f. SECTION E consists of 3 long answer questions carrying 5 marks each.
g. All questions are compulsory.
h. Use of log tables and calculators is not allowed
SECTION A
The following questions are multiple-choice questions with one correct answer. Each question carries 1 mark. There is no internal choice in this section. Q no. 15 to 18 are Assertion Reason type questions.
1. Arrange the following compounds in increasing order of their boiling points:
CH3CHO, CH3CH2OH, CH3OCH3, CH3CH2CH3
A. CH3CH2CH3 < CH3CHO< CH3OCH3 < CH3CH2OH
B. CH3CH2CH3 < CH3OCH3 < CH3CHO <CH3CH2OH
C. CH3CH2CH3 < CH3OCH3 <CH3CH2OH< CH3CHO
D. CH3CH2CH3 < CH3OCH3 < CH3CH2OH < CH3CHO
2. Choose a chemical test to distinguish between ethylamine and aniline.
A. Carbylamine test
B. 2,4-DNP test
C. Azodye test
D. Hinsberg test
3. For a reaction, A + B → Products, the rate law is given by: r = k [A]1/2[B]2. What is the order of reaction?
A. ½
B. 2
C. 2.5
D. 1
4. Write the IUPAC name of the following compound: (CH3)3 CCH2Br
A. 3-Bromo-2, 2-dimethyl propane
B. 1-Bromo-2,2,2-trimethyl ethane
C. 2-Bromo-1,1,1-trimethyl ethane
D. 1-Bromo-2, 2-dimethyl propane
5. When a coordination compound CoCl3.6NH3 is mixed with AgNO3, 3 moles of AgCl are precipitated per mole of the compound. The Structural formula of the complex is
A. [Co(NH3)3Cl3]. 3NH3
B. [Co(NH3)5 Cl]Cl2. NH3
C. [Co(NH3)4 Cl2]Cl.2NH3
D. [Co(NH3)6]Cl3
6. In a reaction, 2A —-> Products, the concentration of A decreases from 0.5 mol L-1 to 0.4 molL-1 in 10 minutes. Calculate the rate during this interval?
A. 0.5 molL-1min-1
B. 0.05 molL-1min-1
C. 0.005 molL-1min-1
D. 0.0005 molL-1min-1
7. The increasing order of basic strengths of given compounds in gaseous phase is
A. NH3, CH3NH2, (CH3)3N, (CH3)2NH
B. NH3, (CH3)2NH, (CH3)3N, CH3NH2
C. (CH3)3N, (CH3)2NH, CH3NH2, NH3,
D. NH3, CH3NH2, (CH3)2NH, (CH3)3N
8. The order of the reaction with value of the rate constant k = 2.3 × 10–5 L mol–1 s –1 is
A. Zero
B. One
C. Two
D. None of these
9. Write the formula of an oxo-anion of Chromium (Cr) in which it shows the oxidation state equal to its group number.
A, Cr2O3
B. CrO2
C. Cr2O7 2-
D.CrO3
10. Which acid from the following would you expect to be the strongest acid?
A. NO2CH2COOH
B. CH3COOH
C. CH3CH2COOH
D. CH2FCOOH
11. The IUPAC name of ionization isomer of [Ni(NH3)3NO2]Cl is
A. Triamminenitrito-O-nickel(II)chloride
B. Triamminenitrito-N-nickel(II)chloride
C. Triamminechloridonickel(II)nitrate
D. Triamminechloridonickel(II)nitrite
12. Which of the following is passed into the cathodic compartment of Hydrogen- Oxygen fuel cell?
A. Hydrogen
B. Oxygen
C. Nitrogen
D. Chlorine
13. Heating methoxybenzene with HI gives
A. Iodobenzene
B. Benzene
C. Iodoethane
D. Phenol
14. The addition of HCN to carbonyl compounds is an example of
A. Electrophilic addition
B. Electrophilic substitution
C. Nucleophilic addition
D. Nucleophilic substitution
15. Given below are two statements labelled as Assertion (A) and Reason (R)
Assertion: Addition of water to but-1-ene in acidic medium yields Butan-1-ol.
Reason: Addition of water in acidic medium to an alkene proceeds through formation of a secondary carbocation.
Select the most appropriate answer from the options given below:
(i) Both assertion and reason are true, and the reason is the correct explanation of the assertion.
(ii) Both assertion and reason are true but the reason is not the correct explanation of assertion.
(iii) Assertion is not true but the reason is true.
(iv) Both assertion and reason are false.
16. Assertion: Hofmann’s bromamide reaction is given by primary amines.
Reason: Primary amines on more basic than secondary amines.
(i) Both assertion and reason are true, and the reason is the correct explanation of the assertion.
(ii) Both assertion and reason are true but the reason is not the correct explanation of assertion.
(iii) Assertion is not true but the reason is true.
(iv) Both assertion and reason are false.
17. Assertion: Sucrose is a nonreducing sugar.
Reason: It has glycosidic linkage.
(i) Both assertion and reason are true, and the reason is the correct explanation of the assertion.
(ii) Both assertion and reason are true but the reason is not the correct explanation of assertion.
(iii) Assertion is not true but the reason is true.
(iv) Both assertion and reason are false.
18. Assertion: Separation of Zr and Hf is difficult.
Reason: Zr and Hf lie in the same group of the periodic table.
(i) Both assertion and reason are true, and the reason is the correct explanation of the assertion.
(ii) Both assertion and reason are true but the reason is not the correct explanation of assertion.
(iii) Assertion is not true but the reason is true.
(iv) Both assertion and reason are false. SE
SECTION B (2 marks)
19. In the following pair of compounds, which will react faster by SN1 mechanism and why?
Ans. reacts faster by SN1 mechanism
it is a tertiary halide and it produces a stable tertiary carbocation
20. Show that in a first order reaction, time required for completion of 99.9% is 10 times of halflife (t 1/2) of the reaction.
Ans.
21.A. Describe the following named reactions with chemical equations.
a. HVZ reaction b. Gattermann Koch reaction
Ans. Each name rn:. Explanation and eqn
OR
B. Describe the following named reactions with chemical equations.
a. Reimer Tiemann reaction b. Stephen reaction
Ans. Each name rn: Explanation and eqn
22. The rate constant for the first order decomposition of H2O2 is given by the following equation: log k = 14.34 – 1.25 × 104K/T
Calculate Ea for this reaction?
Ans.
23. Describe the shape and magnetic behaviour of the complex [CO(NH3)6] 3+
Ans.
24. Calculate ΔrG° and log K. for the following reaction at 298 K.
Ans.
25. Write equation to show what happens when D-glucose is treated with the following reagents.
(i) HI (ii) Bromine water
SECTION C
26. Calculate the boiling point of solution when 4 g of MgSO4 (molar mass =120 g mol-1) was dissolved in 100g of water, assuming MgSO4 undergoes complete ionization. (Kb for water = 0.52 K kg mol-1)
Ans.
27. i) Draw the geometrical isomers of complex [Pt(NH3)2Cl2].
Ans. structures of cis and trans isomers
(ii) On the basis of crystal field theory, write the electronic configuration for d4 ion if Δ0 < P.
Ans. Electronic configuration for d4 ion if Δ0 < P is t2g 3 eg 1 (high spin complex is formed)
(iii) Why a solution of [Ni(H2O)6] 2+ is green while a solution of [Ni(CN)4] 2- is colourless?
Ans. [Ni(H2O)6] 2+ is an outer orbital complex due to weak field ligand H2O and the presence of unpaired electrons undergoes d—d transition (by absorbing red light and shows green colour) while [Ni(CN)4] 2- is an inner orbital complex and has no unpaired electrons hence colourless…
28. Account for the following:
(a) The dipole moment of chlorobenzene is lower than that of cyclohexyl chloride.
Ans. Chlorobenzene has lower dipole moment than cyclohexyl chloride due to lower magnitude of -ve charge on the Cl atom and shorter C – Cl distance. Due to greater S-character, a sp2 -hybrid carbon is more electronegative than a sp3-hybrid carbon. Therefore, the sp2 -hybrid carbon of C – Cl bond in chlorobenzene has less tendency to release electrons to Cl than a sp3 hybrid carbon of cyclohexyl chloride.
(b) Alkyl halides, though polar, are immiscible with water.
Ans. Alkyl halides and polar molecules are held together by dipole-dipole interaction. The molecules of H2O are held together by H- bonds. Since the new forces of attraction between water and alkyl halide molecules are weaker than the forces of attraction already existing between alkyl halide-alkyl halide molecules and water water molecules, therefore alkyl halides are immiscible (not soluble) with water.
(c) n-Butyl bromide has higher boiling point than 30 butyl bromide.
Ans. n-Butyl bromide has higher boiling point than 3 0 -Butyl bromide because it has larger surface area hence have more Van der Waals’ forces.
29. a. Out of CH3—NH2 and (CH3)3N, which one has higher boiling point? Why?
Ans. CH3—NH2 has higher boiling point than (CH3)3N
Reason: CH3—NH2 shows strong intermolecular H bonding whereas (CH3)3N has weak dipole dipole forces.
b. Identify A and B in each of the following:
Ans. A = CH3-CH2-CN, Propanenitrile
B = CH3-CH2– CH2– NH2, Propanamine
30. Explain with the help of equations, the mechanism of acid catalysed hydration of Ethene to form Ethanol.
Ans. mechanism with three steps:
SECTION D
31. Read the passage below and answer the following questions:
Biomolecules are complex molecules that build up living organisms and are required for their growth, maintenance, and ability to reproduce. Carbohydrates are polyhydroxy aldehydes and ketones which are major sources of energy. Proteins are complex nitrogenous polymers of amino acids. Enzymes are highly specific, work at specific pH, moderate temperature, and catalyze biochemical reactions. Hormones perform specific functions and are secreted by endocrine glands. Vitamins are essential for a healthy body. Nucleic acids are polymers of nucleotides and transfer genetic characteristics.
1. Name a disaccharide which on hydrolysis give glucose and galactose.
Ans. Lactose.
2. What type of protein is albumin based on secondary structure?
Ans. Globular protein
3. Mention the linkage by which nucleotides are joined together between 5′ and 3′ atoms of pentose sugar
Ans. Phosphodiester linkage
4. Which vitamin helps in the coagulation of blood?
Ans. Vitamin K
32. At 298 K, the vapour pressure of pure benzene, C6H6 is 0.256 bar and the vapour pressure of pure toluene C6H5CH3 is 0.0925 bar. Two solutions I and II were prepared as follows:
(I) 7.8 g of C6H6 + 9.2 g of toluene
(II) 3.9 g of C6H6 + 13.8 g of toluene The following questions are multiple-choice questions. Choose the most appropriate answer:
(i) The total vapour pressure (bar) of solution 1 is
a. 0.128
b. 0.174
c. 0.198
d. 0.258
(ii) Which of the given solutions has higher vapour pressure?
a. I
b. II
(iii) Solution II is an example of a/an
a. Ideal solution
b. non-ideal solution with a positive deviation
c. non-ideal solution with a negative deviation
d. can’t be predicted
(iv)Mole fraction of benzene in vapour phase in solution 1 is
a. 0.128
b. 0.174
c. 0.734
d. 0.266
SECTION E
33. A. Calculate the time to deposit 1.5 g of silver at cathode when a current of 1.5 A was passed through the solution of AgNO3. (Molar mass of Ag = 108 g mol-1 , 1 F = 96500 C mol -1
Ans.
B. Calculate emf of the following cell at 25 °C: Fe/Fe2+(0.001 M) // H+ (0.01 M)/H2(g) (1 bar)/Pt(s) E°(Fe2+/Fe) = -0.44V, E°(H+ /H2) = 0.00 V
Ans.
C. What type of cell is mercury cell? Why is it more advantageous than dry cell?
Ans. Primary cell. It has more efficiency and its voltage remains constant over a longer period of time…..1m
34. A. The enthalpies of atomization of transition metals are quite high. Why?
Ans. In transition elements, there are large number of unpaired electrons in their atoms, thus they have a stronger inter atomic interaction and thereby stronger bonding between the atoms. Due to this they have high enthalpies of atomization.
B. The transition metals and many of their compounds act as good catalysts. Give reason.
Ans. Due to variable valency and the availability of d-orbitals, they can easily form intermediate products which are converted to products. The sizes of transition metal atoms and ions are also favourable for transition complex formation with the reactants. They can adsorb reactants on their surface and catalyze reactions.
C. Calculate the magnetic moment of a divalent ion in aqueous medium if its atomic number is 26.
Ans. Divalent ion with atomic number 26 is Fe2+
Electronic conf of Fe2+ – [Ar] 3d6
No. of unpaired e (n) = 4
µ = √𝑛(𝑛 + 2) = √24 =4.9 BM …………1m
D. Complete the following equations:
Ans.
35. A. a. An organic compound with the molecular formula C9H10O forms 2,4-DNP derivative, reduces Tollen’s reagent, and undergoes Cannizzaro reaction. On vigorous oxidation, it gives 1,2-benzenedicarboxylic acid. Identify the compound. Write chemical equations for the reactions involved.
Ans. The only o-substituted aromatic aldehyde having molecular formula which show the given reactions is C9H10O is o-ethyl benzaldehyde or 2-Ethyl benzaldehyde….. 1m
Eqn for reaction with Tollen’s reagent ……………..1/2m
Eqn for reaction with 2,4-DNP …………………1/2m
Eqn for Cannizaro reaction of the identified compound …………….1m
b. Carryout the following conversions:
(i) Propanone to Propene
(ii) Benzoic acid to Benzaldehyde
OR
B. a. An organic compound (A) (molecular formula C8H16O2) was hydrolysed with dilute sulphuric acid to give a carboxylic acid (B) and an alcohol (C). Oxidation of (C) with chromic acid produced (B). ‘C’ on dehydration gives But-l-ene. Identify A, B, C and Write equations for the reactions involved.
Ans. A – Butyl butanoate CH3CH2CH2COOC4H9 ….1/2 m
B – Butanoic acid C3H7COOH ….1/2 m
C – But-l-ene CH3CH2CH= CH2 ….1/2 m
b. Give simple chemical tests to distinguish between the following pairs of compounds.
(i) Propanal and Propanone
Ans. i) Iodoform test- Propanone gives yellow ppt with NaOH and I2 whereas propanal does not react. (1m)
(ii) Phenol and Benzoic acid
Ans. ii) NaHCO3 test / Neutral FeCl3 test- mention the characteristic change observed. (1m)