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XII CBSE
TM
CHEMISTRY
Path to success KOTA (RAJASTHAN )
Important Questions 2015
1.
Crystalline solid are anisotropic in nature. What does this statement mean?
2.
Which is stoichiometric defect in crystals increases the density of a solid?
3.
Calculate the packing efficiency of a metal crystal for a simple cubic lattice.
4.
Silver crystallizes in face-centered cubic unit cell. Each side of this unit cell has a length of 400 pm. Calculate
the radius of the silver atom. (Assume the atoms just touch each other on the diagonal across the face of the
unit cell. That is each face atom is touching the four corner atoms.)
5.
In an ionic compound the anion (N −) from cubic close type of packing. While the cation (M+) ions occupy one
third of the tetrahedral voids. Deduce the empirical formula of the compound and the coordination number
of (M+) ions.
6.
The density of copper metal is 8.95 g cm⎯3. If the radius of copper atom be 127.8 pm, is the copper unit cell
simple cubic, body centered cubic or face-centered cubic? (Given: atomic mass of Cu = 63.54 g mol⎯1 and NA =
6.02 X 1023 mol⎯1)
7.
8.
How would you account for the following?
(i)
Frenkel defects are not found in alkali metal halides.
(ii)
Schottky defects lower the density of related solids.
(iii)
Impurity doped silicon is a semiconductor
An element has a body – centered cubic (bcc) structure with a cell edge of 288 pm. The density of the element
is 7.2g/cm3. How many atoms are present in 208 g of the element?
9.
Calculate the distance between Na+ and cl- ions in NaCl crystal if its density is 2.165gcm-3
10.
Silver crystallizes in face-centered cubic unit cell. Each side of this unit cell has a length of 400 pm.
Calculate the radius of the silver atom (Assume the atoms just touch each other on the the diagonal across
the face of the unit cell. That is each face atom is touching the four corner atoms.
11.
The density of copper metal is 8.95 g cm-3. If the radius of copper atom be 127.8 pm, is the copper unit
cell simple cubic, body centered cubic or face-centered cubic?( Given: Atomic mass of Cu=63.54 g mol-1 and
NA= 6.02 X 1023mol-1)
12.
How would you account for the following(i)
Frenkel defects are not found in alkali metal halides.
(ii)
Schottky defects lower the density of related solids.
(iii)
Impurity doped silicon is a semiconductor.
(iv)
Crystalline solid are anisotropic in nature.
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13.
14.
Explain the following properties giving suitable examples:
(i)
Ferromagnetism
(ii)
(iv)
n-type semiconductors (v)
Paramagnetism
(iii)
Ferrimagnetisms
F-centers
(vi)
Forbidden zone of an insulator
Which point defect of its crystal (i) decreases the density of a solid (ii) increases the density of a solid(iii) does
not change the density of the solid?
15.
Name the non-stoichometric point defect responsible for colour in alkali halides.
16.
Calculate the packing efficiency of a metal crystal for a simple cubic lattice & BCC.
17.
What is the number of atoms per unit cell in a face-centered cubic (fcc) structure?
18.
What mass of NaCl (molar mass = 58.5 g mol ⎯1) must be dissolved in 65 g of water to lower the freezing point
by 7.5 ͦ C ? The freezing point depression constant, Kf for water is 1.86 kg mol⎯1. Assume van’t Hoff factor for
NaCl is 1.87.
19.
Define ‘ebulioscopic constant’
[
20.
Non-ideal solutions exhibit either positive or negative deviations from Raboult’s law. What are these
deviations and why are they caused? Explain with one example for each type.
21.
A solution prepared by dissolving 1.25 g of oil of winter green (methyl salicylate) in 99.0 g of benzene has a
boiling point of 80.31 ͦ C. Determine the molar mass of this compound. (B.P. of pure benzene = 80.10 ͦ C and Kb
for benzene = 2.53 ͦ C kg mol ⎯1)
22.
Calculate the freezing point of an aqueous solution containing 10.50g of MgBr2 in 200 g of water.(Molar
mass of MgBr = 184 g) (Kf for water =1.86 k kg mol-1)
23.
Explain- What will be happen when red blood cells are placed in water?
Why is an increase in temperature observed on mixing chloroform with acetone?
Two liquids A and B boil at 145°C and 190° C respectively. Which of them has a higher vapour
pressure at 80° C?
24.
State Henry’s law correlating the pressure of a gas and its solubility in a solvent and mention two applications
of the law.
25.
Define osmotic pressure. How it is that measurement of osmotic pressure is more widely used for determining
molar masses of macromolecules than the rise in boiling point or fall in freezing point their solutions?
26.
27.
Explain the following:
(i)
Two liquids A and B are mixed. The resulting solution is found to be colour.
(ii)
Raoult’s law in its general form in reference to solutions.
(iii)
Abnormal molecular mass.
Differentiate between molarity & molality in a solution. What is the effect of temperature change on molarity
and molality in a solution?
28.
The vapour pressure of ethanol and methanol are 44.5 and 88.7 mm Hg respectively. An ideal solution is
formed at the same temperature by mixing 60g of ethanol and 40g of methanol. Calculate the total vapour
pressure of the solution and the mole fraction of methanol in the vapour phase.
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29.
The degree of dissociation of Ca(NO3)2 in dilute aqueous solution contain 7.0 g of the salt per 100g of water at
100° C. is 70%. If vapor pressure of water at 100°C is 760mm, calculate the vapor pressure of the solution.
30.
(a) A current of 1.50 A was passed through an electrolytic cell containing AgNO3 solution with inert electrodes.
The weight of Ag deposited was 1.50g. How long did the current flow?
(b) Write the reactions taking place at the anode and cathode in the above cell.
(c)Give reactions taking place at the two electrodes if these are made up of Ag.
31.
(a) State the relationship amongst cell constant of a cell, resistance of the solution in the cell and conductivity
of the solution. How is molar conductivity of a solute related to conductivity of its solution?
(b) A voltaic cell is set up at 25° C. with the following half-cells: Al |Ag3+ (0.001 M) and Ni|Ni2+ (0.50 M)
Calculate the cell voltage [
32.
°
|
°
= −0.25 ,
= −1.66 ]
3+|
The resistance of a conductivity cell containing 0.001 M KCl solution at 298 K is 1500 what is the cell constant if
conductivity of 0.001 M KCl solution at 298 K is 0.146× 10
33.
−1
What is the principle of fuel cell. Write the recharging reactions occurring in (i) a lead storage battery
(ii) Nicad cell.
34.
Write the chemical equations for all the steps involved in the rusting of iron. Give any one method to prevent
rusting of iron. Explain Cathodic/Electrical protection
35.
Two half reactions of an electrochemical cell are given below:
(
). +8
(
(
)+5
)→
→
(
(
)+2
)+4
,
°
( ),
°
= +1.51
= +0.15
Construct the redox equation from the standard potential of the cell and predict if the relation is reactant
favoured or product favoured
36
Given that the standard electrodes potentials ( ° ) of metals are
K+/K= -2.93 V,Ag+/Ag=0.80 V,Cu2+/Cu=0.34 V
Mg2+/Mg=-2.37V,Cr3+/Cr = -0.74 V, Fe2+/Fe = -0.44 V
Arrange these metals in an increasing order of their reducing power.
37.
Define- (i) Order of reaction (ii) Activation energy of a reaction (iii) a pseudo first order reaction (iv) rate law.
38.
A certain reaction is 50% complete in 20 minutes at 300 K and the same reaction is again 50% complete in 5
minutes at 350K.calcualte the activation energy if it is a first order reaction. (R = 8.314 JK-1 mol-1: log 4 = 0.602)
39.
Decomposition of phosphate (PH3) at 120° . proceeds according to the equation:
4
( ) → ( ) +6
(
)
It is found that this reaction follows the following rate equation: Rate = k [PH3]. The half life of PH3 is 37.9 s at
120° . How much time will be required for ¾ of PH3 to decompose? What fraction of the original amount of
PH3 will be remain unrecompensed after 1 minute
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40.
The reaction, 2NO + Br2 → 2NOBr proceeds by the following mechanism:
(i)
+
+
(ii)
2
Suggest a rate law constant with the mechanism.
41.
The thermal decomposition of HCO2H is a first order reaction with rate constant of 2.4 × 10⎯3 s⎯1 at a certain
temperature. Calculate how long will it take for three-fourths of initial quantity of HCO2H to decompose. (log =
0.25 = ⎯0.6021)
42.
Explain what is observed when
(i) An electric current is passed through a sol
(ii) A beam of light is passed through sol
(iii) An electrolyte (say NaCl) is added to ferric hydroxide sol.
(iv) Controll’s smoke prepecitator is fitted at the mouth of the chimney used in factories.
43.
What is the difference between multimolecular and macromolecular colloids? Give one example of
each type. How are associated colloids different from these two types colloids ?
44.
Why is ferric chloride preferred over potassium chloride in case of a cut leading to bleeding ?
45.
What are lyophillic and lyophillic sols? Give one example of each type. Which one of these two types Of
sol is easily coagulated and Why?
46.
Explain- (a) Adsorption of a gas on the surface of solid is generally accompanied by a decrease in
entropy. Still it is spontaneous process
(b)How does an increase in temperature affect both physical as well as chemical adsorption?
47.
Define the following- (i) Peptization (ii) Reversible sols (iiii) shape-selective catalysis (iii) Electrophoresis
(vi) Brownian movement (vi) Tyndal effect (viii) Coagulatation of colloids
48.
Explain the role of each of the following in the extract of the metals from their ores:
(i) CO in the extraction of nickel
49.
(ii) Zinc in the extraction of silver
(iii) Silica in the extraction of copper
(iv) Cryolite in the electrolyte reduction of alumina
(v) Pine oil in froth floatation method
(vi) NaCN in the extraction of silver from silver ore
Describe the principal controlling each of the following processes:
(i) Preparation of cast iron from pig iron
(ii) Preparation of pure alumina (Al 2O3) from bauxite ore
(iii) Vapour phase refining of titanium metal (iv)Froth floatation method of concentration of a sulphide ore
(v)Electrolytic refining of a metal
(vi) Recovery of silver after silver ore was leached with NaCN.
50.
The extraction of Au by leaching with NaCN involves both oxidation and reduction. Justify giving equations.
51.
What is a slag? What are fluxes? How are the useful?
52.
What name is given to carbon reduction process for extracting the metal?
53.
What is meant by the term pyrometallurgy ?
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54.
55.
Explain the following :
XeF2 is a linear molecule without a bent

Nitrogen is relatively inert as compared to phosphorus

H2S is less acidic than H2Te

The electrolyte gain enthalpy with negative sign is less for oxygen than that sulphur

Phosphorus shows greater tendency for catenation then nitrogen.

Fluorine never acts as the central atom in polyatomic interhalogen compounds.

Fluorine does not exhibit any positive oxidation state

The majority of known noble gas compounds are those of Xenon

Red Phosphorus less reactive than white phosphorus

NF3 is an exothermic compound but NCl3 is not

Nitrogen does not form pentahalides

In aqueous solution HI is a stronger acid than HCl

Ammonia is a stronger bases then phosphine

Sulphur in vapour state exhibits a paramagnetic behaviour

Bond angle in PH3 molecules lesser than that in NH3 molecule

Bi(v) is a stronger oxidising agent than Sb(v)

Bond dissociation energy of F2 is less than that of Cl2

All the P-Cl bonds in PCl5 are not equivlent

SF6 is kinetically inert

All the P-Cl bonds in PCl5 molecule are not equivalent.

Solid phosphorus pentachloride behave as an ionic compound.
Write balanced chemical equation for the following reactions(i) Chlorine is passed through hot concentrated NaOH solutions
(ii) XeF6 is hydrolysed.
(iii) Excess of SO2 reacts with sodium hydroxide solutions.
(iv) Orthophosphorus acid is heated.
(v) PtF6 and Xenon are mixed together.
56.
Complete the following chemical reaction equations
(i) HgCl2 (aq)+PH3
(ii) Si
(iii) Ca3P2 +H2O
(iv)XeF2+H2
(v) XeF2 +H2O
(vi) PH3+HgCl2
2+
(vii) Cu (aq) + NH3(aq)
(x) I-(aq)+H2O(l)+O3
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(viii) F2(g)+H2O(l)
(ix)P4(s)+NaOH(aq)+H2O(l)
57.
Draw the structure of –
(i) H3PO4 (ii)XeF4 (iii)H2S2O8 (iv)HClO4 (v)N2O5 (vi)XeOF4 (vii)H2S2O7 (viii)BrF3 (ix) XeF2 (x)XeO3
58.
Assign reason for each of the following:
Transition metals act as catalysts.

Chromium group elements have the highest melting point in their respective series.

Transition metals from coloured complexes

The metallic radii of the third (5d) series of transition elements are virtually the same as those of the
corresponding members of the second series.

There is greater range of oxidation states among the actinoids than the lanthanoids.

Copper(I) has d10 configuration, while copper (II) has d9 configuration, still copper(II) is more stable in
aqueous solution than copper(I)

Among the lanthanoids, Ce(II) is easily oxidixed to Ce(IV).

Fe3+|Fe2+ redox couple has less positive electrode potential than Mn3+|Mn2+ couple.

CrO42- is a strong oxidising agent while MnO42- is not.

The lowest oxidation state of manganese is basic while the highest is acidic.

Mn(II) shows maximum paramagnetic character amongst the divalent ions of the first transition series.

The enthalpies of atomization of transition elements are high.

The greatest numbers of oxidation states are exhibited by the members in the middle of a transition
series.
59.
60.
61.

Although Co2+ ion appears to be stable , it is easily oxidised to Co3+ ion in the presence of a strong ligand

The highest oxidation state of a metal is exhibited in its oxides or fluoride
Complete the following chemical equation for reactions:

MnO4-(aq)+C2O42-+H+(aq)

Cr2O72-+Fe2+(aq)+H+(aq)

MnO4-(aq)+S2O32-(aq)+H2O(l)

Cr2O72-+H2S(g)+H+(aq)

Cr2O72-+I-(aq)+H+(aq)

MnO4-(aq)+Fe2+(aq)H+(aq)
What happen when :
Pyrolusite is fused with K2CO3 in the presence of air.

Ln (lanthanoid )reacts with water

K2Cr2O7 is heated with NaCl and Conc. H2SO4.

KMnO4 is heated.
Describe the preparation of K2Cr2O7 from iron chromite one what is effect of increasing pH on solution of
K2Cr2O7
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62.
A mixed oxide of iron and chromium FeO.Cr2O3 is fused with sodium carbonate in the presence of air to
Form a yellow coloured compound (A).On acidification of the compound (A) from an orange coloured
Compound (B).Which is a strong oxidising agent. Identify A and B, also write the chemical reactions
63.
Explain the following terms giving a suitable example in each case: Ambient ligand, Denticity of a ligand,
Linkage isomerism, An outer orbital complex, A bidentate ligand, Hydrate isomerism.
64.
For the complex [Fe(en)2Cl2]Cl , identify the following: Oxidation number of iron
Hybrid orbitals and shape of the complex.
65.
Explain the following:
(i) CO is stronger ligand than NH3 for many metals
(ii) Square planar complexes with coordination number of four exhibit geometrical isomerism whereas
Tetrahedral complexes do not
(iii) Synergic bonding in metal carbonyls
66.
Explain Crystal field splitting in an octahedral field, draw a sketch of show the splitting of d-orbital’s in an
Octahedral crystal field. State for a d6 ion the actual configuration in an octahedral crystal field is decided
by the magnitude of ∆0 and P.
67.
Write IUPAC Names of the following coordination compounds
(a)[CO (NH3)6]Cl3
68.
(b)[Co(NH3)5Cl]Cl2 (c) K3[Fe(CN)6] (d)K3[Fe(C2O4)3] (e) K2[PdCl4] (f) [Pt(NH3)2Cl(NH2CH3]Cl.
Write the state of hybridisation, shape and the magnetic behaviour of the following(i) [Cr(NH3)4Cl2] Cl(ii) [Co(en)3]Cl3 (iii) K2[Ni(CN)4]
69.
Explain the following(i) Hofmann Degradation Reaction (ii) Kolbe’s Reaction
(iii) Wolff Kishner
(iv) Cannizzaro
(v) Clemmensen reduction
(vi) HVZ reaction
(vii) Etard’s reaction (viii) Coupling reaction
(ix) Gattermann reaction
(x) Cross Aldol condensation
(xi) Carbylamine reaction
70. Give chemical tests to distinguish between the following pairs of compounds –
71
(i)
(i)Acetone and Propionaldehyde
(ii) Ethanol and Methanol
(iv) Benzoic acid and ethyl benzoate
(v) Benzaldehyde and acetophenone
(vi) Ethylamine and aniline
(vii) Acetaldehyde and Benzaldehyde
(viii) Sec. and Tertiary Amine
(ix) Phenol & Benzyl Alcohol
(x) Ethoxy Ethane & Ethanol
(xi) Formic Acid & Acetic Acid
State reason for the following:
Gabriel phthalimide is not used for the preparation of aromatic amines.
(ii) Primary amines have higher boiling point than tertiary amines
(iii) pkbvalue for aniline is more than that for methylamine.
(iv) Ethylamine is soluble in water whereas aniline is not soluble in water.
(v) Aldehyde are more reactive than ketones towards nucleophiles.
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(iii) Phenol and Benzoic Acid
(vi) The boiling points of aldehyde and ketones are lower than of the corresponding acids.
(vii) The aldehyde and ketones undergo a number of addition reactions but carboxylic acids does not
(viii) Ortho-nitro phenol is more acidic than ortho-methoxyphenol
(ix) Phenol is more acidic than ethanol.
(x) Amines are less acidic than alcohols of comparable molecular masses
(xi) There are two NH2 groups in semicarbazide,however only one is involved in the formation of semicarbazone
72
How will you bring about the following conversions?
(i) Propanone to propene
(ii) Benzaldehyde to benzophenone
(iii) Ethanol to 3-hydroxybutanal
(iv) Phenol to asprin
(v) Phenol to Picric acid
(vi) Aniline to Iodobonzene
(vii) Benzoquinone from phenol (viii) Benzoic acid from ethylbenzene
(x) Ethanenitrile to ethanol
(ix) Acetaldehyde to Lactic Acid
(xi) Aniline to nitrobenzene (xii) Bromobenzene to 1-phenyl ethanol
(xi) p-Fluorotoluens to p-fluorobenzaldehyde (xiv) Benzyl chloride to benzyl alcohol,
73
An organic compound (A)on treatment with acetic acid in presence of sulphuric acid produces an ester (B).
A on mild oxidation gives C. C with 50% KOH followed by acidification with dil HCl gives A and D. D with PCl5
followed by reaction with ammonia gives E. E on dehydration produces hydrocyanic acid. Identify A,B,C,D,E.
Write the equations for the reactions involved.
74
An unknown Aldehyde ‘A’ on reacting with alkali gives a β-hydroxy- aldehyde, which losses water to from an
unsaturated aldehyde ,2-butenal. Another aldehyde with the formula C7H8O
(i) Identify A and B. (ii) Write the sequence of reaction involved
(iii) Name the product when ‘B’ reacts with Zinc amalgam and hydrochloric acid
75
An organic compounds A has molecular formula C8H16O2. It gets hydrolysed with dilute sulphuric acid and gives
a carboxylic acid B and an alcohol C. with chromic acid also produced B. C on dehydration reaction gives But-1ene. Write equations for the reation involved
76
An organic compound ‘A’ with molecular formula C5H8O2 is reduced to n-pentane on treatment with Zn –
Hg/HCl. ‘A’ forms a dioxime with hydroxylamine and gives a positive idoformtest. Identify the compound A
and deduce its structure.
77
Arrange the following compounds
(i) in an increasing order of their acids strengths: (CH3)2CHCOOH,CH3CH2CH(Br)COOH,CH3CH(Br)COOH
(ii) in the increasing order of their boiling points: CH3CH2CH2CHO,CH3CH2CH2CH2OH,H5C2-O- C2H5,
CH3CH2CH2CH2CH3
(iii) in an increasing order of their basic strengths: C6H5NH2,C6H5N(CH3)2,(C6H5)2NH and CH3NH2
(iv) in an increasing order of their basic strength in aqueous solution 1°2°,3° amines
(v) in an increasing order of SN2 displacement: 1-Bromopentane or 2-bromo-2 methylbutane
78
Write the structural formula of 3-oxopentanal, 4-chloropentan-2-one
79
Write the IUPAC name of : CH3CH(Br)CH2CONHCH3
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80
Describe the mechanism of the formation of diethyl ether from ethanol in the presence of concentrated
Sulphuric acid or Dehydration of Alcohol in the presence of concentrated Sulphuric acid
81
Write the mechanism of reaction of HI with ether.
82
State one uses each of DDT and iodoform.
COOH
(i)
SOCl2
COOH
(ii)
(iii)
(iv)
CH2
CH2
C6H5CHO
CH3CH2Cl
Heat
CHO
H2NCONHNH2
NaCN
(A)
reduction
(B)
Ni/H2
(v)
C6H5N2Cl + H3PO2 + H2O
O
(v)
R
C
NH2
LiAlH4
H2O
83
Explain the meanings of the following terms- (i) Invert sugar (ii) Peptide linkage (iii) Denaturation of proteins
(iv) Phosphodiester linkage (v) Pyranose structure of glucose (vi) Anomers of glucose (vii) glycosidlc linkage
(viii) Pernicious anaemia(ix) DNA strands are complementary
84
Mention three such facts/ reactions about glucose which cannot be explained by its open and structure
85
Name the four base present in DNA .Which one is not present in RNA
86
Name the products of hydrolysis of sucrose, cellulose, starch. Why is sucrose not a reducing sugar
87
Differentiate between fibrous proteins & globular proteins
88
What happens when glucose is treated with bromine water, HI, Hydroxyl amine? What these reactions tell
about the structure of glucose?
89
What is essentially the differences between - from of glucose and - form of glucose? Explain.
90
Describe what you understand by primary structure and secondary structure of proteins.
91
State clearly what are known as nucleosides and nucleotides. What is meant by reducing sugar?
92
Name two water soluble vitamins ,their sources and the diseases caused due to their deficiency in diet
93
Write the names and structure of the monomer of the following polymer and one uses: Buna-S, Neoprene,
Nylon-6, Nylon-2--nylon-6, Teflon , Bakelite, Dacron, PHBV, Melamine, Natural rubber, Glyptal, PMMA
94
Name the sub- group into which polymers are classified on the basis of magnitude of intermolecular forces.
Give an example of elastomers
95
What is meant by copolymerisation? What are biodegradable polymers .Give an example
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96
Differentiate the following pairs of polymers based on the property mention against each- Novalac and
Bakelite (structure ) : Buna-N and Terylene (intermolecular forces of attraction)
97
Explain HDP and LDP?
98
Give one example of an artificial sweetners used by the diabetic patients
99
Name the substance that can be used as an antiseptics as well as a disinfectant. What is tincture of iodine
100
Do as directed What is meant by the ‘ broad spectrum antibiotics’
 In order to wash clothes with water containing dissolved calcium bicarbonate ,which agent will you prefer and
why- soaps and synthetics detergents ?Give one advantage of soap over synthetics detergents
 Name one substance which can act as both: (i)Analgesic and antipyretic
 Agonist and antagonist, Competitive and non-competitive inhibitors.
 What are the main constituents of dettol?
 Explain the following types of substances with one suitable example, for each case-Cationic detergents, Food
Preservatives ,Analgesics, Non-ionic detergent, Antifertility drugs
 What are analgesics drugs? How are they classified and when are they usually recommended for use ?
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