SAMPLE PAPER -4 Time Allowed: 3 Hrs

SAMPLE PAPER -4
CLASS-XII
SUB - CHEMISTRY
Time Allowed: 3 Hrs
Maximum Marks: 70
General Instructions:
1. All questions are compulsory.
2. Question No. 1-8 are very short answer questions and carry 1 mark each.
3. Question No. 9-18 are short answer questions and carry 2 marks each.
4. Question No. 19-27 are also short answer questions and carry 3 marks each.
5. Question No. 28-30 are long answer questions and carry 5 marks each.
6. Use log tables if necessary, use of calculators is not allowed.
Q1 Identify the reaction order from the rate constant value = 3.2  10-5 litre mol-1 sec-1.
Q2 Write ant two features which distinguish physisorption from chemisorption.
Q3 Write IUPAC name of ionization isomer of [Cr(H2O)5SO4]Br.
Q4Complete the following reaction:
Peroxide NaI
CH3-CH=CH2 + HBr X
Y
Acetone
Q5 Chloroacetic acid is more acidic than acetic acid. Give reason.
Q6Write the IUPAC Name of
CH2ClCOCH(CH3)CONH2
Q7What are the ultimate products of digestion of proteins?
Q8 Arrange the following in the order of their increasing basic character:
C6H5NH2, (C2H5)2NH, (C2H5)3N and NH3.
Q9Gold (atomic mass = 197, atomic radius = 0.144 nm) crystallizes in a face centered unit
cell. Determine the
density of gold. (NA = 6.022  1023 )
Q10 What is H2-O2 fuel cell? Write the reactions occurring at cathode and anode.
Q11 a) Explain the F- centres with suitable example.
www.cpprashanthschemistry.com
Page 1
b) A compound formed by element A and B crystallizes in the cubic structure where A
atoms are at the corner
of a cube and B atoms are at the face centres. Find out the formula of the compound.
Q12a) State Kohlrausch law of independent migration of ions.
b) Calculate Λm 0 for acetic acid. Given that:
Λm 0(HCl) = 426Scm2mol-1, Λm 0(NaCl) = 126 Scm2mol-1,
Scm2mol-1.
Λm 0(CH3COOH) = 91
Q13 (a) Complete the following reactions.
(a) XeF4 + H2O →
(b)HgCl2 + PH3
Q14 Explain the following name reactions .
(a) Diazotization Reaction (b) Carbylamine reaction.
Q15How are the following conversions carried out?
(a) Propene to 2-Propanol.
(b) Phenol to Toluene
Q16 For the reaction
N2(g) + 3H2(g)  2NH3(g)
If [NH3] / t = 4  10-8 mol L-1 Sec-1, what is the value of - [H2] / t ?
OR
The rate constant for the decomposition of ethyliodide in the reaction
C2H5I(g)  C2H4(g) + HI(g)
At 600K is 1.60  10-5 s-1 . Its energy of activation is 209kj/mol. Calculate the rate
constant
of the reaction at 700K.
Q17 a) What is ambidentate ligand? Give one example.
b) A solution of [Ni(H2O)6]2+ is green colour. Explain.
Q18Explain the mechanism of hydration of ethene to yield ethanol.
Q19a)In the Button cell, widely used in watches, the following reaction takes place:
Zn(s) + Ag2O(s) + H2O → Zn+2(aq) + 2Ag(s)+ 2OH-(aq)
CalculateE0cell and standard Gibbs energy for the reaction.
www.cpprashanthschemistry.com
Page 2
(Given: E0Ag+ / Ag = + 0.80 V ; E0Zn+ / Zn = - 0.76 V )
b) Why does molar conductivity of a strong electrolyte like KCl decrease slightly with
increasing concentration?
Q20 a) Explain the following observations:
i) An emulsion is subjected to high speed centrifuging.
ii) Ferric hydroxide sol coagulates on addition of a solution of potassium sulphate.
b) What is shape selective catalysis? Write one example.
Q21 a)Describe the role of the following:
i)
NaCN in the extraction of silver from a silver ore.
(ii) Iodine in the refining of titanium.
(iii) Cryolite in the metallurgy of aluminium.
OR
Describe the principle involved in each of the following processes of metallurgy :
(i) Froth floatation method
(ii) Electrolytic refining of metals
(iii) Zone refining of metals
Q22 Give reasons for the following:
a) H3PO3 is diprotic(dibasic).
b) The electron gain enthalpy with negative sign for fluorine is less than that for
chlorine, still fluorine is a stronger oxidising agent than chlorine.
c) Sulphur exhibit tendency of catenation but Oxygen does not.
Q23Draw the structure of the following :
(a) XeOF4 (b) H2S2O8 d) HOClO
Q24 a) Account for the followings:
(i) Dipole moment of chlorobenzene is lower than that of cyclohexyl chloride.
(ii) Grignard reagent should be prepared under anhydrous conditions.
b) Which one of the following pairs of halogen compounds undergo S N2 faster and Why?
Q25Nita’s mother is suffering from pernicious aneamia. She gets tired & is not able to do her work properly.
Nita helps her in the household works.
i) Name the vitamin which caused the deficiency disease.
ii)Give two sources for that vitamin.
www.cpprashanthschemistry.com
Page 3
iii) What values are shown by Nita?
Q26a) Give an example of a synthetic rubber and mention its main advantage.
b) What is a Biodegradable polymer? Give an example of biodegradable aliphatic polyester.
c) Write the structure of monomers of the following polymers.
i) Teflon
ii) Dacron
Q27Explain the following terms with one example in each case:
a) Broad spectrum antibiotics
b) Trasquilizers
c) Food Preservatives
Q28a) State the condition resulting in reverse osmosis.
b) Mention a large scale use of phenomenon called reverse osmosis?
c) On dissolving 3.24 g of sulphur in 40 gof benzene. Boiling point of solution was higher than
that of benzene by 0.81 K. Kb value for benzene is 2.53 K kg mol-1.
What is the molecular formula of sulphur? (Atomic mass of S = 32 g mol-1)
OR
(a) Show that relative lowering in vapour pressure is a colligative property.
(b) Calculate molarity, molality and mole fraction of KI, if the density of 20% (mass/mass)
aqueous KI is 1.202 gm/ml. ( K = 39, I = 127).
Q29 (a) Complete the following reactions:
i)
Cr2O72- (aq) + H2S (g) + H+ (aq)
ii)
MnO4- + H2O + I-
(b) Explain the following:
(i)Actinoids show large number of oxidation state.
(ii)Cr2+ is reducing in nature while with the same d-orbital configuration (d4)
Mn3+ is an oxidising agent.
(iii) Cu+ ion is not stable in aqueous solutions.
OR
(a) Write the steps involved in the preparation of :
i)
KMnO4 from K2MnO4
ii)
K2CrO7 from Na2CrO4
(b) Complete the following reactions:
i)
Cr2O72- (aq) + Fe2+(g) + H+ (aq)
ii)
Cu2+ (aq) + I- (aq)
(c) Whytransition metals exhibits highest oxidation state in oxides & fluorides.
Q30a) Give chemical tests to distinguish between the following:
www.cpprashanthschemistry.com
Page 4
i) Benzoic acid and ethyl benzoate
ii) Benzaldehyde and acetophenone.
b) An organic compound (A) has molecular formula C5H10. It does not reduce Tollen’s
reagent but forms an orange precipitate with 2,4- DNP reagent. It forms a carboxylic
acid (B) with molecular formula C3H6O2 when treated with alkaline KMnO4, yellow
precipitate on treatment with NaOH and I2, under vigorous conditions
On oxidation it gives ethanoic acid and propanoic acid. Sodium salt of (B) gave a
hydrocarbon (c) in
Kolbe’s Electrolytic Reduction. Identify (A),(B) and(C) and write the reaction involved.
OR
a) Completeeachsynthesisbygivingmissingreagentsorproducts inthefollowing:
i)
CONHNH2
(ii )C6 H 5CHO NH
2

b) An organic compound A(C3H6O) is resistant to oxidation but forms compound B(C 3H8O)
on reduction which reacts with HBr to form bromide C. C forms a Grignard reagent which
reacts with A to give D (C6H14O).Identify the compounds A, B, and C and give their structures
Explain the reactions involved.
www.cpprashanthschemistry.com
Page 5
SAMPLE PAPER -4
ANSWER KEY
Time Allowed: 3 Hrs
Maximum Marks: 70
1 Second order
1
2 Any two features which distinguish physisorption from chemisorption.
½+½
3 [Cr(H2O)5 Br] SO4 , pentaaquabromidochromium(III) sulphate
½
½+
4 X= CH3CH2CH2Br ; Y = CH3CH2CH2I + NaBr ½ + ½
5 Due to presence of electron withdrawing chlorine atom(-I effect) in chloroacetate ion,
H+ions are easily formed.
1
6 4- Chloro-2-methyl-3-oxobutanamide
1
7- Amino acids
½+½
8 C6H5NH2 NH3 (C2H5)3N  (C2H5)2NH
9Given:M = 197, Z = 4, r = 0.144nm, NA = 6.022 x 1023
For fcc:4r = 2 a ; a = 4r2 = 4  1.414 0.144 1 + 1
= 0.407 nm = 0.407 10-7 cm
d = ZM/a3 NA
d= 4 x 197 / (0.407 10-7 )3
= 19.4 g/ cm3.
1
10Cells which produce electrical energy directly from the combustion of fuels1 + ½ + ½
such as H2. CO, CH4.
Anode: 2H2(g) + 4OH- (aq) 
4H2O(l)
+ 4eCathod: O2(g) + 2H2O(l) + 4e-
4OH- (aq)
www.cpprashanthschemistry.com
Page 6
11a)The electrons entrapped in anion vacancies.
Example : Due to F- centres the excess of LiCl makes it pink or any other example.
1
b) AB3
½+½+
12a) The law states that limiting molar conductivity of an electrolyte can be represented1 + ½
+½
as the sum of the individual contributions of the anion and cation of the electrolyte.
b)
Ë°m (HAc) = 0H+ + 0Ac
0CH3COOH = 0 CH3COONa + 0 HCI - 0 NaCI
=
( 91 + 426 – 126 )S cm2 mol-1
=
391cm2mol-1
13a) 6XeF4 + 12H2O 2XeO3+ 4Xe + 24HF + 3O2 1 + 1
b)3HgCl2 + 2PH3Hg3P2 + 6HCl
273-2780C
14 a) C6H5NH2 + NaNO2 +2 HCl C6H5N2X + NaCl + 2H2O1 + 1
b) R-NH2(10 amine) + CHCl3 + 3KOH(alc.) R – NC + 3KCl + 3H2O
H2O/H+
15 a) CH2 = CH– CH3
1+1
CH3 – CH – CH3
І
OH
b) C6H5OH
C6H6C6H5CH3
Zn dust
F.C. A
16-[N2] / t = - 1/3 [H2] / t =
+1/2 [NH3] / t
1+1
[NH3] / t = - 1/3 [H2] / t = ½  4  10-8 × 8
= 6 10-8 mol L-1 sec-1
OR
log K2/K1 = Ea/2.303R [1/T1 – 1/T2 ]
log K2 = log K1 + Ea/2.303R [1/T1 – 1/T2 ]
= -4.796 + 2.599 = -2.197
K2 = 6.36 X 10-3
www.cpprashanthschemistry.com
Page 7
17a)Ambident ligand: a unidentate ligandwhich can co-ordinate to the centralmetal
½+½+1
atomthroughmore than one co-ordinating bond.e.g.NO2- or any other.
b) Hybridization is sp3d2and presence of two unpaired electrons.
18 i) Protpnation of water to formed hydronium ion.
+½+½ +½
ii) Formation of carbocation intermediate.
iii) Nucleophilic attack by water on carbication
iv) Deprotanation.
½
19a) E0cell = E0cathod -E0anode = + 0.80 + 0.76= + 1.56 V ; n = 2½ + ½ + ½ + ½ + 1
∆rG0= -nFE0cell = - 2 x 96500 x 1.56 = -301080 j mol-1 = -301.08 kj mol-1
b) Because greater number of ion-pairs(K+ and Cl-) are formed per unit volume due to
greater
increase in interionic attractions.
20 a) i) Demulsificarion occurs.1 + 1 + ½ + ½
ii) Due to oppositely charged ions, coagulation take place.
b) Shape selective catalysis: A catalyst whose catalytic action depends upon its pore
structure
And molecular sizes of the reactants as well as the products is called shape selective
Catalysts and the catalytic action is called shape selective Catalysis.
For example Zeolites ( ZMS-5)
21(i) Role of NaCN in the extraction of silver is to do the leaching of silver ore in
+1+1
the prescence of air from which the silver is obtained later by replacement.
or
4Ag(s) + 8CN–(aq) + 2H2O + O2(g) 4[Ag(CN)2]– + 4OH–
(ii) Iodine is heated with titanium to form a volatile compound which on further
heating decomposes to give pure titanium.
Or
Ti(impure) + 2I2TiI4

TiI4 Ti(pure) + 2I2
(iii) Cryolite lowers the melting point of mixture of alumina in the extraction of
aluminium / increase the conductivity of mixture.
www.cpprashanthschemistry.com
1
Page 8
OR
(i) Froth Floatation method:- The mineral particles become wet by oils while
the gangue particles by water.
(ii) Electrolytic refining: Crude metal is made as anode and pure metal as cathode.
When current is passed through electrolyte of same metal ions then pure
metal gets deposited at cathode and impurities settle at bottom of anode.
(iii) Zone Refining:- The impurities are more soluble in the melt than in the solid
state of the metal.
22 (a)Due to presence of two P-OH bonds.
1+1+1
(b) Because of lower bond dissociation enthalpy of F 2 and high hydration enthalpy of F.
(c ) S-S bond strength is stronger than O-O. Catenation property α M-M bond strength.
23 Correct structure of a, b and c
1+1 + 1
24 (a) i) Chlorobenzene has sp2 hybridisation whereas cyclohehylchloride has sp3. 1 + 1 + ½ + ½
Therefore chlorobenzene hasgreater S character and is less polar.
ii) Because Grignard reagent reacts with water to form alkanes
RMgX +H2O  R-H + Mg(OH)X
(c) i) Cyclohexyl chloride, because it is 20 alkyl halides.
ii) Pentyl iodide, because Iodine is good leaving group.
25 a) i) vitamin-B 12, ii)meat,fish & curd., iii) love & affection for mother
.
26 a) Neoprene 1 + 1 + ½ + ½
Used in making conveyor belts in coal mines. (any other example)
c) Polymerswhich undergo bacterial degradation in the environment and
are thus ecofriendly. Example PHBV
d) Correct structure of monomer of Dacron and Teflon
27 (a) An antibiotics which is effective in inhibiting the growth of several types ½ + ½ + ½ +
½+½+½
of organism simultaneously. Tetracylin or any other example..
(b) Those chemicals which are used to remove mentle stress are called tranquilizers.
Equanil or any other example.
(c) Food preservatives: are the compounds which prevent spoilage of food due
to microbial growth. eg: sodium benzoate, vinegar (any one example)
www.cpprashanthschemistry.com
Page 9
28 (a) Pressure larger than osmotic pressure is applied to the solution side, i.e, 1 + 1
P > (osmotic pressure).
(b) Desalination of sea water
(c )
MB = Kb WB 1000 / Tb WA ½ + ½ + 1 +1
= 2.53  3.24  1000 / 0.81  40
= 253 g mol-1
32 g mol-1 have sulphur = 1 atom
253 g mol-1 have sulphur = 1  253/32 = 7.8 8
Hence molecular formula of sulphur is S 8
OR
(a) Psolution = Xsolvent x P0solvent;
Psolution
Xsolvent
----------------- =
0
P solvent
Subtract each side from 1 ,
Psolution
1------------------ = 1--Xsolvent = Xsolute
P0solvent
P0solvent -- Psolution
________________
= Xsolute
0
P solvent
(b) Mass of solvent H2O = 100—20 = 80 gm 0.08 kg,
Molar mass of KI = 166,
20 / 166
m = --------------- = 1.5 Ans.
0.08
Volume of solution = M/d = 100 / 1.202 = 83.2 ml = 0.0832 L
20 / 166
M = ---------------- = 1.44 Ans
0.0832
www.cpprashanthschemistry.com
Page 10
Moles of KI
20/166
Mole fraction = ---------------- = -------------------- = 0.0263 Ans
Total moles
20/166 + 80/18
29(a) i) Cr2O72- (aq) + 3H2S (g) + 8H+ (aq) 2Cr2+ + 3S + 7H2O1 +1
(ii) 2MnO4- +2 H2O +I- 2 MnO2 + IO3- + 4OHb) i) Electrons from ns orbitals as well as (n-1)d-orbitals take part in bond formation. 1
+1+1
This is possible due to small energy difference between ns and (n-1)d- orbitals.
ii)Cr2+is reducing as its configuration changes from d4 to d3, the latter having
half filled t2g levelwhereas Mn3+ to Mn2+ results in half filled orbitals (d5).
d5 stable confriguration for Mn2+.
iii) Because Copper(I) ion is unstable in aqueous solution and undergoes
disproportionation reaction.
OR
(a)
i) 3MnO42- +4H+ MnO2 + 2MnO4- + 2H2O
Electrolytic oxidation
MnO42in alkaline medium
MnO4-
ii) Na2CrO7+ 2KCl K2Cr2O7 + 2NaCl.
b) i)Cr2O72- (aq) + 6Fe2+ (aq) + 14H+ (aq) 2Cr2+ + 6Fe3+ + 7H2O
ii)2Cu2+ + 4I– Cu2I2 + I2
c)Oxygen and fluorine are most electro-negative elements.
30 ( a) (i) Sodium bicarbonate test: Warm each compoundwithNaHCO3,1 + 1
Benzoic acid gives brisk effervescence ofCO2 gaswhereas ethyl benzoate does not
respond to this test
(Other relevant test)
(ii) Iodoform test.Warm each organic compound with I2 and NaOH solution.
Acetophenone (C6H5COCH3)Yellow precipitates of iodoform are formed
With Benzaldehyde does not respond to this test.(Other relevant test )
www.cpprashanthschemistry.com
Page 11
b) (A) Phenyl methyl ketone (B) Benzoic acid 1 + 1 +1
H2O
Reactions: C6H5COCH3 + 2, 4- DNP
2,4- DNP derivative
C6H5COOH 
C6H5COCH3
C6H5COONa + CHI3
H2CrO4I2 + NaOH
(B)
(B)
OR
(a) (i)a) B2H6. H2O2 / OH- b) PCC
ii) C6H5CHO + NH2CONHNH2 C6H5CH=NNHCONH2 + H2O
OH
OR
RedІ
HBr
Mg CH3COCH3
(b) CH3COCH3 ----- CH3CHCH3 -------------- CH3-CH-CH3 ------------CH3-CH-CH3 ----------------
A
(B)
- H2O
I (C) I
Br
MgBr
OMgBr
OH
I
H2 O
I
CH3-C-CH3 --------------------- CH3-C-CH3 (D) 2.3 dimethyl butan-2-ol
I
I
CH(CH3)2
CH(CH3)2
www.cpprashanthschemistry.com
Page 12