PREBOARD I-EXAMINATION (2022-23)
CLASS -XII
SUB- CHEMISTRY
CHEMISTRY PAPER 1
(THEORY)
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Maximum Marks: 70
Time Allowed: Three hours
(Candidates are allowed additional 15 minutes for only reading the paper.
They must NOT start writing during this time).
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This paper is divided into four sections – A, B, C and D.
Answer all questions.
Section A consists of one question having sub-parts of one mark each.
Section B consists of ten questions of two marks each.
Section C consists of seven questions of three marks each, and Section D
consists of three questions of five marks each.
Internal choices have been provided in one question each in Section B,Section C
and Section D.
All working, including rough work, should be done on the same sheet as, and adjacent to
the rest of the answer.
The intended marks for questions or parts of questions are given in brackets [ ].
Balanced equations must be given wherever possible and diagrams where they are helpful.
When solving numerical problems, all essential working must be shown.
In working out problems, use the following data:
Gas constant R = 1.987 cal deg-1 mol-1 = 8.314 JK-1 mol-1 =
0.0821 dm3 atm K-1mol-1
1 l atm = 1 dm3 atm = 101.3 J. 1 Faraday = 96500 coulombs.
Avogadro’s number = 6.023 x 1023
.
Question 1
(A)Fill in the blanks by choosing the appropriate word/words from those given in the
brackets: [4x1]
[ohm-1, Great, paramagnetic, Raoult’s, ohm-1 cm-1, negative, ideal, diamagnetic, ferromagnetic, non-
ideal]
(i) Solutions which strictly obey ……… law is called …………. Solutions.
(ii) More ………. the standard reduction potential of a substance, the ……… is its ability to displace
hydrogen from acids.
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(iii) The transition metals show …………. character because of the presence of impaired electrons
and Cu+ is ……. because its electronic configuration is [Ar] 3d 10.
(iv) The unit of conductance is ………. and that of specific conductance is …..........
(B)Complete the following statements by selecting the correct alternative from the choices given:
[4x1]
(i)For a dissociated solute in solution the value of van’t Hoff factor is:
(a) Zero (b) One
(c) Greater than one (d) Less than one
(ii)The quantity of electricity required to deposit 1.15 g of sodium from molten NaCl (Na = 23, Cl = 35.5)
is:
(a) 1 F (b) 0.5 F
(c) 0.05 F (d) 1.5 F
(iii) In the complexes [Fe(CN)6]3- and [Pt(en) (H2O)2 (NO2) (Cl)]2+ the respective oxidation numbers of
central metal atoms are:
(a) +3 and+4
(b) +6 and+4
(c) +6 and +3
(d) +3 and +3
(iv) In the dehydration of alcohols to alkenes by heating with concentrated sulphuric acid, the initiation
step is:
(a) formation of carbocation
(b) formation of an ester
(c) protonation of the alcohol molecule
(d) elimination of water
(c) Match the following [4 x1]
COLUMN A COLUMN B
(i) Colligative property (a) Nernst equation
(ii) Rate of reaction (b) Osmotic pressure
(iii) EDTA (c) Arrhenius equation
(iv) Electrochemical cell (d) Hexadentate
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D) Answer the following questions: [2 X 1]
(i) Assertion: The boiling points of aldehydes and ketones are higher than hydrocarbons and
ethers of comparable molecular masses.
Reason: There is a weak molecular association in aldehydes and ketones arising out of the
dipole-dipole interactions.
(a) Both assertion and reason are true and the reason is the correct explanation of
assertion.
(b) Both assertion and reason are true but the reason is not the correct explanation for
assertion.
(c) Assertion is true but the reason is false.
(d) Assertion is false but the reason is true.
(ii) Assertion: Transition metals are good catalysts.
Reason: V2O5 or Pt is used in the preparation of H2SO4 by contact process.
(a) Both assertion and reason are true and the reason is the correct explanation of
assertion.
(b) Both assertion and reason are true but the reason is not the correct explanation for
assertion.
(c) Assertion is true but the reason is false.
(d) Assertion is false but the reason is true.
SECTION B – 20 MARKS
Question 2 46 gms of ethyl alcohol is dissolved in 18 gms of water. Calculate the mole fraction of ethyl
alcohol. (at. wt of C =12, O =16,H = 1) [2]
Question 3 Give a reason on for the following: [2]
(i) Mn2+ is more stable than Fe2+ towards oxidation to +3 state. (At. no. of Mn = 25, Fe = 26)
(ii) Transition elements usually form coloured ions.
Question 4An organic compound A with the molecular formula C 3H8O3 reacts with oxalic acid at 110°C
to give a monocarboxylic acid B. B gives a silver mirror with Tollen’s reagent and
reduces acidified potassium permanganate solution. Identify A and B.
[2]
Question 5Arrange the following compounds in the ascending order of their basic strength and give
reasons for your answer: [2]
Methylamine, Aniline, Ethylamine, Diethyl ether
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Question 6 [2]
A substance decomposes by following first-order kinetics. If 50% of the compound is
decomposed in 120 minutes, how long will it take for 90% of the compound to
decompose?
Question 7 [2]
Write the IUPAC names of the following:
(i) [CO(NH3)4SO4]NO3
(ii) K[Pt(NH3)Cl3]
Question 8 [2]
(i)How is iodoform prepared from ethanol? Give a balanced equation. (ii) What will
be the product formed when chlorobenzene is heated with sodium metal in the
presence of dry ether?
Question 9 [2]
The following electrochemical cell is set up at 298 K:
Zn/Zn2+(aq) (1M)//Cu2+(aq) (1M)/Cu
Given →E Zn2+/Zn =−0.761V, E Cu2+/Cu = +0.339V
(i) Write the cell reaction.
(ii) Calculate the emf and free energy change at 298 K.
Question 10 [2]
Give one chemical test to distinguish between the following pairs of compounds:
(i) Acetone and phenol.
(ii) Formic acid and acetic acid.
Question 11 [2]
Write the IUPAC name of [Co(en) 2Cl2] + ion and draw the structures of its geometrical
isomers.
SECTION C – 21 MARKS
Question 12 [3]
For the reaction : 2H2 + 2NO2H2O + N2 , the following rate data was obtained:
Calculate the following:
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(i) The overall order of a reaction.
(ii) The rate law.
(iii) The value of rate constant (k).
Question 13 [3]
An organic compound A has the molecular formula C 7H6O. When A is treated with NaOH
followed by acid hydrolysis, it gives two products B and C. When B is oxidized, it gives A when A
and C are each treated separately with PCl 5, they give two different products D and E.
(i) Identify A, B, C, D and E.
(ii) Give the chemical reaction when A is treated with NaOH and name the reaction.
Question 14 [3]
(I) Deficiency of which vitamin causes the following diseases:
(a) Scurvy
(b) Night blindness
(ii) Write two differences between globular and fibrous proteins.
Question 15 [3]
A solution of lactose-containing 8.45 g of lactose in 100 g of water has a vapour pressure of
4.559 mm of Hg at 0°C. If the vapour pressure of pure water is 4.579 mm of Hg, calculate the
molecular weight of lactose.
Question 16 [3]
Give balanced equations for the following name reactions:
(i)Friedel-Crafts reaction (alkylation)
(ii) Williamson’s synthesis
(iii) Aldol condensation
Question 17 [3]
An aromatic organic compound [A] on heating with NH 3 and Cu2O at high pressure gives [B],
The compound [B] on treatment with an ice-cold solution of NaNO 2 and HCl gives [C], which on
heating with Cu/HCl gives compound [A] again. Identify the compounds [A], [B] and [C].
OR
How can the following conversions be brought about:
(i) Nitrobenzene to benzene diazonium chloride.
(ii) Propanoic acid to ethylamine.
(iii) Benzoic acid to benzaldehyde.
Question 18 [3]
-4 -1
The specific conductance of a 0.01 M solution of acetic acid at 298 K is 1.65 × 10 ohm . The
molar conductance at infinite dilution for H+ ion and CH3COO– ion is 349.1 ohm-1 cm2 mol1
and 40.9 ohm-1 cm2 mol-1 respectively. Calculate:
(i) Molar conductance of the solution.
(ii) Degree of dissociation of CH3COOH.
(iii) Dissociation constant of acetic acid.
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SECTION D – 15 MARKS
Question 19 [5]
(i) Starting with methyl magnesium bromide, how will the following compounds be
synthesized?
(a) Acetaldehyde
(b) Acetone
(c) Acetic acid
(ii) Draw the resonating structures of chlorobenzene.
Question 20 [5]
(i) Write the structures of optical isomers of the complex ion [Co(en) 2Cl2] + (ii)[CoF6]3- is a
coordination complexion.
(a) What is the oxidation number of cobalt in the complex?
(b) How many unpaired electrons are there in the complex?
(c) State the magnetic behaviour of the complex. (d)Give the IUPAC name of the
complex.
Question 21 [5]
(i) Write the mathematical expression relating the variation of the rate constant of a
reaction with temperature.
(ii) How can you graphically find the activation energy of the reaction from the above
expression?
(iii) The slope of the line in the graph of log k (k = rate constant) versus 1T is -5841.
Calculate the activation energy of the reaction.
OR
(i)What will be the vapour pressure of a solution containing 5 moles of sucrose (C 12H22O11) in 1
kg of water, if the vapour pressure of pure water is 4.57 mm of Hg? [C = 12, H = 1, O = 16]
[3]
(ii) Consider the following cell reaction at 298 K: [2]
2+
2Ag+ + Cd → 2Ag + Cd
The standard reduction potentials (E°) for Ag+/Ag and Cd 2+ /Cd are 0.80 V and -0.40 V
respectively:
(a) Write the cell representation.
(b) What will be the emf of the cell if the concentration of Cd 2+ is 0.1M and that of Ag+ is 0.2
M?
