Date :16.01.2023
No.of Pages: 07
BANGALORE SAHODAYA SCHOOLS COMPLEX
PRE BOARD EXAMINATION - JANUARY 2023
CHEMISTRY (Code – 043)
CLASS XII
Maximum Marks: 70
SET 1
Time : 3hrs
General Instructions:
Read the following instructions carefully.
1.
2.
3.
4.
5.
6.
7.
8.
There are 35 questions in this question paper with internal choice.
SECTION A consists of 18 multiple-choice questions carrying 1 mark each.
SECTION B consists of 7 very short answer questions carrying 2 marks each.
SECTION C consists of 5 short answer questions carrying 3 marks each.
SECTION D consists of 2 case-based questions carrying 4 marks each.
SECTION E consists of 3 long answer questions carrying 5 marks each.
All questions are compulsory.
Use of log tables and calculators is not allowed
SECTION A
(Q.No 1 – 14) The following questions are multiple choice questions with one correct answer.
Each question carries 1 mark. There is no internal choice in this section.
1. The molar conductivity of two electrolytes A and B (Λm) is being
1⁄
plotted against the square root of concentration 𝐶 2 as shown in
the graph. Λm becomes Λ0m (limiting molar conductivity)
When
a) c → 0
b) c → ∞
c) c → 1
d) c → 2
2. What is true about the cell constant of a conductivity cell?
a) It changes with change of electrolyte.
b) It changes with change of concentration of electrolyte.
c) It changes with temperature of electrolyte.
d) It remains constant for a given cell.
3. The rate constant of zero-order reactions has the unit
a) s-1
b) mol L-1 s-1
c) L2 mol-2 s-1
d) L mol-1 s-1
4. When temperature is increased by 20oC, the rate of reaction and the rate constant becomes
a) double
b) triple
c) quadruple
d) remains the same
Class XII – Chemistry – Set 1
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5. Activation energy of a chemical reaction can be determined by
a) determining the rate constant at standard temperature.
b) determining the rate constant at two different temperatures.
c) determining the probability of collision.
d) using catalyst.
6. Transition elements form alloys easily because they have
a) same atomic number
b) same electronic configuration
c) nearly same atomic size
d) none of the above
7. Write the IUPAC name for K2[PdCl4].
a) Potassium tetrachloropalladium(II)
c) Potassium tetrachloridopalladium(II)
b) Potassium tetrachloridopalladate(II)
d) Tetrachlorinepalladate(II)potassium
8. Which of the following biologically significant coordination molecules has Magnesium as its
core atom?
a) Vitamin B12
b) Haemoglobin
c) Chlorophyll
d) Carboxypeptidase-A
9. Choose the correct order of boiling points of isomeric dichlorobenzene.
a) para>ortho>meta b) meta>ortho>para c) ortho>para>meta d) para>meta>ortho
10. What is the correct order of reactivity of alcohols in following reactions?
(Anhy.ZnCl2)
R–OH + Conc.HCl
R–Cl + H2O
a) 10 >20 >30
c) 30 >20 >10
b) 10 <20 >30
d) 30 >10 >20
11. The reaction of C(CH3)3Br with NaOCH3(alc) forms the product
a) CH3OC(CH3)2Br
b) CH3C(CH3) = CH2 c) C(CH3)3ONa
d) CH3CH(CH3) CH=CH2
12. A single compound of the structure OHC - CH2 CH(CH3) CH2 CO CH3 is obtained from ozonolysis of
which of the following compounds?
a)
b)
c)
d)
13. IUPAC name of the product formed by the reaction of Methyl amine with two moles of
Ethyl chloride is
a) N,N–Dimethylethanamine
b) N,N–Diethylmethanamine
c) N–Methylethanamine
d) N–Ethyl–N–Methylethanamine
Class XII – Chemistry – Set 1
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14. The order of basic strength of amines in aqueous solution is
a) (CH3)3N > (CH3)2NH > CH3NH2 > NH3
b) CH3NH2 > (CH3)2NH > (CH3)3N > NH3
c) NH3 > (CH3)3N > (CH3)2NH > CH3NH2
d) (CH3)2NH > CH3NH2 > (CH3)3N > NH3
(Q. No. 15-18): Each of the following questions consist of two statements,
one is Assertion and the other is Reason. Choose the correct option.
(a) Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) Both Assertion and Reason are true but Reason is not the correct explanation of
Assertion.
(c) Assertion is true but Reason is false.
(d) Assertion is false but Reason is true.
15. Assertion(A): Sucrose is non reducing sugar.
Reason (R): Sucrose has glycosidic linkage.
16. Assertion(A): Tertiary amines do not react with CH3COCl.
Reason(R): Tertiary amines have highest boiling point among isomeric 10, 20 And 30 amines.
17. Assertion (A): Ethers are stored in dark coloured bottles.
Reason (R): In the presence of sunlight and air ethers form Peroxides which may cause
explosion.
18. Assertion (A): Thorium shows +4 Oxidation state.
Reason (R): Th+4 has noble gas configuration.
SECTION B
(Q. No. 19-25): This section contains 7 questions with internal choice in two questions.
The following questions are very short answer type and carry 2 marks each.
19. Consider the following equations
Au3+(aq) + 3e → Au(s) , E0 = 1.50 V
-
AuCl4 + 3e → Au(s) + 4Cl, E0 = 1.0 V
a) Which of these species is a better oxidising agent?
b) At which electrode would gold be deposited?
20.
21.
A first order reaction takes 69.3 minutes for 50% completion. What is the time needed for
80% of the reaction to get completed?
(Given; log 5 = 0.6990, log 8 = 0.9030, log 2 = 0.3010)
Identify the reaction order from each of the following rate constants.
a) k = 2.3 x 10-5 Lmol-1s-1
b) k = 3 x 10-4 s-1
Class XII – Chemistry – Set 1
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22.
What is spectrochemical series? Explain the difference between a weak field ligand and
strong field ligand.
23.
Write the formula of the main product formed in the following reactions
a) CH3Br + AgF →
b) CH3CH2Br + NaI →
OR
a) CH3CH2CH=CH2 + HBr →
b) C2H5OH + SOCl2 →
24.
Give simple chemical tests to distinguish between the following pairs of compounds:
a) Propanal and Propanone
b) Ethanal and Benzoic acid
25.
Give reason for the following observations:
a) pKb of aniline is lower than that of m-nitroaniline.
b) Aniline does not undergo Friedel-Crafts reaction.
OR
a) Aniline on nitration gives meta products in addition to ortho and para products.
b) Aromatic diazonium salts are more stable than alkyl diazonium salts.
SECTION C
(Q. No. 26-30): This section contains 5 questions with internal choice in one question.
The following questions are short answer type and carry 3 marks each.
26.
Using the Valence bond theory, explain the following in relation to the Complex [Ni (CN)4]2a) Type of hybridization b) Magnetic behaviour
c) Geometry of the complex.
27.
a) Write the Van’t Hoff’s factor for the complete dissociation of Aluminium chloride.
b) Henry’s constant for Argon is 40 Kbar in water. Determine molal concentration of
Argon in water when it is stored above water at 10 bar pressure.
(1+2)
28.
a) Write the mechanism of the following reaction:
CH3CH2CH2CH2Br + KCN (alc) → CH3CH2CH2CH2CN + KBr
b) How will you convert 2,4,6–trinitrochlorobenzene to Picric acid?
OR
(2+1)
a) Write the reaction mechanism of conversion of tertiary butyl chloride to tertiary butyl
alcohol.
b) How do you convert Chlorobenzene to Phenol?
29.
Explain the following with an example
(3)
a) Lucas Reagent Test b) Williamson’s Ether synthesis c) Manufacture of Phenol from Cumene
30.
a) Explain the following conversions.
i) Aniline to p-bromoaniline ii) Benzene diazonium chloride to p-hydroxyazobenzene
b) Write the structure of N,N–Diethylbutan-1-amine.
(2+1)
Class XII – Chemistry – Set 1
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SECTION D
(Q. No. 31-32): The following questions are case-based questions.
Each question has an internal choice and carries 4 (1+1+2) marks each.
31.
Read the passage given below and answer the following questions:
The solubility of gases increases with increase of pressure. William Henry made a systematic
investigation of the solubility of a gas in a liquid. According to Henry's law "the mass of a
gas dissolved per unit volume of the solvent at constant temperature is directly proportional
to the pressure of the gas in equilibrium with the solution". Dalton during the same period
also concluded independently that the solubility of a gas in a liquid solution depends upon
the partial pressure of the gas. Different gases have different KH values of the same
temperature suggests, KH is a function of nature of gas.
a) What is the slope of the line given in graph?
b) With respect to solubility, what is the significance of KH?
c) i) Why does solubility of a gas in liquid decreases with increase in temperature?
ii) Why do carbonated beverages fizz out rapidly when the sealed can is opened?
OR
(1+1+2)
c) i) What is the cause of anoxia at high altitude?
ii) Why do scuba divers carry air diluted with Helium?
32. There are 13 vitamins known till today. Let’s know the history about how vitamins are
discovered.
By the end of mid 1800 scientists had discovered that pathogens caused various diseases. It
was assumed that patchy skin, failing eye-sight etc. were also caused by germs instead of
vitamin deficiency. Dutch Bio- scientist Dr. Christiaan reported in 1895, that chickens that ate
polished rice developed beri-beri. He was awarded nobel prize in 1929 for his contribution i n
discovery of vitamins. In the beginning Vit- C was called scurvy vitamin and Vit – B was
called beri-beri vitamin. When a batch of rats were fed with a diet heavy in lard and olive oil,
they died but another batch that were fed with the addition of tiny amount of butter fat they
survived. McCollum identified vitamin in butter fat as Fat Soluble Vitamin A. Vitamin B12
and Vitamin D were discovered later. Now we also know vitamin E, K and H.
a) Name two vitamins that are stored in liver and adipose tissues.
b) Out of vitamin C and A which vitamin cannot be stored in our body and why?
c) Identify the Vitamin which helps in blood clotting and name the source of this vitamin.
Class XII – Chemistry – Set 1
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OR
(1+1+2)
c) Identify the vitamin which is fat soluble and anti-oxidant. What are the sources of this
vitamin and its deficiency disease?
SECTION E
(Q. No. 33-35): The following questions are long answer type and carry 5 marks each.
Two questions have an internal choice.
33.
a) State Kohlrausch’s law. Write its mathematical expression for salt AxBy.
b) Eocell of a given redox reaction is 2.71 V.
Mg(s) + Cu2+ (0.01M) → Mg2+ (0.001M) + Cu(s)
Calculate Ecell for the reaction. Write the direction of flow of current when an external
opposite potential applied is
i) Less than 2.71 V ii) Greater than 2.71 V
(2+3)
OR
a) On the basis of E0 values identify which amongst the following is the strong reducing agent?
Cl2(g) + 2 e– → 2ClEo = +1.36 V
MnO – + 8H+ + 5e- → Mn2+ + 4H O
Eo = +1.51 V
4
2–
Cr2O7
2
+ 14H+ + 6e– → 2Cr3+ + 7H2O
Eo = +1.33 V
b)
i)
ii)
iii)
Define molar conductivity.
Identify the nature of electrolyte on
the basis of the above plot. Justify
your answer.
Can we determine Λom of weak
electrolyte graphically? Give
reason.
(1+1+1+2)
34. a) Complete the following chemical equations:
i) MnO4 - + C2O4 2- + H+ →?
ii) KMnO4
Heat
?
b) Account for the following
i) Transition metals are less electropositive than s- block elements.
ii) Osmium shows up to +8 oxidation state.
iii) The third ionization enthalpy of Manganese (Z=25) is exceptionally high.
(2+3)
Class XII – Chemistry – Set 1
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35. a) An aromatic compound ‘A’ (Molecular formula C8H8O) gives a positive 2, 4-DNP test. It
gives a yellow precipitate of compound ‘B’ on treatment with iodine and sodium hydroxide
solution. Compound ‘A’ does not give Tollen’s or Fehling’s test. On severe oxidation with
potassium permanganate forms a carboxylic acid ‘C’ (Molecular formula C7H602). Identify
A, B and C and write all the reactions involved.
b) Can Gattermann-Koch reaction be considered similar to Friedel-Crafts acylation?
Discuss with chemical reactions.
OR
(3+2)
a) An organic compound ‘A’, having the formula, C3H8O, on treatment with copper at 573 K
gives ‘B’. ‘B’ does not reduce Fehling’s solution but gives a yellow precipitate of the
compound ‘C’ with I2/NaOH. Deduce the structure of A, B and C.
b) Give plausible explanation for each of the following.
i) There are two -NH2 groups in semicarbazide. However only one is involved in the
formation of semicarbazones.
ii) During esterification, the ester or water should be removed as soon as it is formed.
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Class XII – Chemistry – Set 1
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