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Important Questions

Topic wise important questions for CBSE 12 Chemistry Board Exam 2017 are given below.

SOLID STATE

1) Explain the terms

a) lattice point
b) crystal lattice
c) unit cell.

2) Account for the following:

a) Glass panes fixed to windows of old buildings becomes slightly thicker at the bottom than at the top.
b) NaCl(s) does not conduct electricity but it conducts either in molten state or in aqueous solution.
c) Diamond is a non conductor while graphite is a conductor of electricity.
d) Diamond is hard while graphite is soft.
e) Graphite is a lubricant.
f) Ionic solids are hard and brittle.
g) MgO and NaCl are ionic solids but MgO has higher melting point than NaCl.
h) NaCl exhibit schottky defect and not frenkel defect.

3) Account for the following:

a) Glass panes fixed to windows of old buildings becomes slightly thicker at the bottom than at the top.
b) NaCl(s) does not conduct electricity but it conducts either in molten state or in aqueous solution.
c) Diamond is a non conductor while graphite is a conductor of electricity.
d) Diamond is hard while graphite is soft.
e) Graphite is a lubricant.
f) Ionic solids are hard and brittle.
g) MgO and NaCl are ionic solids but MgO has higher melting point than NaCl.
h) NaCl exhibit schottky defect and not frenkel defect.
4)Explain the terms a) anisotropy b) isotropy. Why is crystalline solid anisotropic while amorphous solid isotropic in nature?

5) In terms of band theory explain the differences between conductor , insulator, and semi conductor. Draw a neat diagram to show the valence band and conduction band in conductor, insulator and semi conductor.

6)Silver chrysalises in FCC with an edge length 409 pm and density 10.5g/cm3. Calculate the Atomic mass of silver.

7)An element crystallizes in bcc. a = 288 pm. How many atoms are there in 208 grams of this elements?

SOLUTIONS

1) Give two examples each of a solution :

(a)showing positive deviation from Raoult’s Law.
(b)showing negative deviation from Raoult’s Law

2) What is the maximum value of van’t Hoff factor (i) for Na2SO4. 10H2O?
3) How much urea (mol. mass 60 g mol–1) must be dissolved in 50g of water so that the vapour pressure at the room temperature is reduced by 25%? Also calculate the molality of the solution obtained.

4) Why is the freezing point depression considered as a colligative Property?
5) Osmotic pressure of a 0.0103 molar solution of an electrolyte was found to be 0.75 atm at 27°C. Calculate Van’t Hoff factor.

ELECTROCHEMISTRY

1) Write short notes on reduction and oxidation potentials

2) What is cell constant? How it is determined?

3) What do you mean by

( i) negative standard electrode potential and
(ii) positive standard electrode potential ?

4) Zinc electrode is constituted at 298 K by placing Zn rod in 0.1 M aq solution of zinc sulphate which is 95 % dissociated at this concentration. What will be the electrode potential of the electrode given that EθZn2+/Zn= – 0.76 V.

5) Calculate the pH of following cell: Pt, H2/ H2SO4, if its electrode potential is0.03V.

CHEMICAL KINETICS

1) Give one example of pseudo first order reaction

2) What do you understand by ‘rate of reaction’?How it is expressed?How it is the rate of reaction determined?

3) If the decomposition of nitrogen oxide as 2N2O5 ────> 4NO2 + O2 follows a first order kinetics.

(i) Calculate the rate constant for a 0.05 M solution if the Instantaneous rate is 1.5 x 10-6 mol/l/s?
(ii) What concentration of N2O6 would give a rate of 2.45 x 10-5 mol L-1s-1 Rate = 2.45 x 10-5 mol L-1s-1

4) The half-life period of two samples are 0.1 and 0.4 seconds. Their initial Concentrations are 200 and 50 mol L-1 respectively. What is the order of reaction?

5) Derive the equation for the rate constant for a first order reaction. What would be the units of the first order rate constant if the concentration is expressed in mole per litre and time in seconds

SURFACE CHEMISTRY

1) Name the catalyst used in the following process :

(a) Haber’s process for the manufacture of NH3 gas.
(b) Ostwald process for the manufacture of nitric acid.

2) Why do colloidal particles show Brownian movement?

3) Write the differences between adsorption and absorption?

4) Define the term peptization and mention its cause.

5) State “Hardy Schulze Rule” with one example.

ISOLATION OF ELEMENTS

1) Write the reaction involved in the extraction of copper from low grade ores.

2) Zinc is used but not copper for the recovery of metallic silver from the complex [Ag(CN)2]–, although electrode potentials of both zinc and copper are less than that of Ag. Explain why?

3) State the principles of refining of metal by the following methods.

(a)Zone refining
(b) Electrolytic refining
(c) Vapour phase refining

4) What is hydrometallurgy? Give one example where it is used for metal Extraction

5) Although aluminium is above hydrogen in the electrochemical series, it is stable in air and water. Why?

p-BLOCK ELEMENTS

1) In group 15 elements, there is considerable increase in covalent radius from N to P but small increase from As to Bi. Why

2) The boiling point of PH3 is lesser than NH3. Why?

3) Why HF is the weakest acid and HI is the strongest.

4) Draw the structures of BrF3, XeOF4, XeO3 using VSEPR theory

5) Write the conditions that favour the formation of ammonia gas along with the reactions involved in Haber’s Process.

6) (a)Hydrolysis of XeF6 is not regarded as a redox reaction. Why?
(b) Write a chemical equation to represent the oxidising nature of XeF4.

d- and f-BLOCK ELEMENT

1) How do acidified KMnO4 and acidified K2Cr2O7 reacts separately with (a)SO2, (b) H2S (c) FeSO4?

2) Write the ionic equations of KMnO4 (acidified) with (a) oxalate ion (b) Mohr salt (c) NO2– and (d) Iron (II) oxalate.

3) Why Mn2+ compounds are more stable than Fe2+ compounds towards oxidation to their +3 state?

4) Arrange the following monoxides of transition metals on the basis of decreasing basic character TiO, VO, CrO, FeO.

5) Complete the following equations :

(a) MnO2 + KOH + O2 →
(b) Na2Cr2O7 + KCl->

COORDINATION COMPOUNDS

1)Give the IUPAC name of [Pt Cl2(NH2CH3)(NH3)2] Cl.
2)Which is more stable? K3[Fe(CN)6] or K4[Fe(CN)6]

3) Account for the following —
(i)[NiCl4]2– is paramagnetic while [Ni(CO)4] is diamagnetic though both are tetrahedral.
(ii)[Fe(H2O)6]3+ is strongly paramagnetic whereas [Ni(NH3)6]2+ weakly paramagnetic.
(iii)[Co(NH3)6]3+is an inner orbital complex whereas [Ni(MH3)6]2+ is in outer orbital complex

4)Compare the following complexes with respect to their shape, magnetic behaviours and the hybrid orbitals involved.
(a) [CoF6]3–
(b) [Cr(NH3)6]3+
(c) [Fe(CN)6]

5) Calculate the magnetic moments of the following complexes :

(i) [Fe(CN)6]4–
(ii) [CoF6]3

HALOALKANES AND HALOARENES

1) Write the structure of following halogen compounds

(i) 2-chloro-3-methylpentane
(ii) 2-(2-chlorophenyl)-1-iodooctane
(iii) 1-bromo-4-sec-butyl-2–methylebenzene.
(iv) p-bromotoluene.
(v) chlorophenylmethane

2) Arrange the following in the increasing order of properly indicated :

(i) bromomethane, chloromethane, dichloromethane. (Increasing order of boiling points).
(ii) 1-chloropropane, isopropyl chloride, 1-chlorobutane (Increasing order of boiling point)
(iii) dichloromethane, chloroform, carbon terachloride. (Increasing order of dipole moment.
(iv) CH3F, CH3Cl, CH3Br, CH3l (Increasing reactivity towards nucleophilic substitution and increasing order of dipole moment)
(v) o,m.p-dichlorobenzenes (Increasing order of melting points).

3) How will you bring about the following conversions?

(i) benzene to 3-bromonitrobenzene
(ii) ethanol to but-1-yne
(iii) 1-bromopropane to 2-bromopropane
(iv) benzene to 4-bromo-1-nitrobenzene
(v) aniline to chlorobenzene
(vi) 2-methyl-1-propene to 2-chloro-2-methylpropane
(vii) ethyl chloride to propanoic acid
(viii) but-1-ene to n-butyl iodide
(ix) benzene to phenylchloromethane.
(x) tert-butyl bromide to isobutyl bromide.

4) Give reasons for the following :
(i) The bond length of C–Cl bond is larger in haloalkanes than that in haloarenes.
(ii) Although alkyl halides are polar in nature but are not soluble in Water.

5) Which compound in each of the following pairs will react faster in SN2 reaction with OH–and why?

(i) CH3Br or CH3I
(ii) (CH3)3CCl or CH3C

ALCHOLS,PHENOLS AND ETHERS

1) Describe the following reactions with example :
(i) Hydroboration oxidation of alkenes
(ii) Acid catalysed dehydration of alcohols at 443K.
(iii) Williamson synthesis
(iv) Reimer-Tiemann reaction.
(v) Kolbe’s reaction
(vi) Friedel-Crafts acylation of Anisole

2) How will you convert

(i) propene to propan-l-ol.
(ii) anisole to phenol
(iii) butan-2-one to butan-2-ol
(iv) ethanal to ethanol
(v) phenol to ethoxybenzene
(vi) 1-phenylethene to 1-phenylethanol

3) Give reason for the following :

(i) The C–O–C bond angle in dimethyl ether is (111.7°)
(ii) Alcohols have higher boiling points than ethers of comparable molecular masses.
(iii) Phenols are more acidic than alcohols.
(iv) Nitrophenol is more acidic than o-methoxyphenol.
(v) Phenol is more reactive towards electrophilic substitution reaction than benzene

4) Give a chemical test to distinguish between the following pair of compounds.
(i) n-propyl alcohol and isopropylalcohol
(ii) methanol and ethanol
(iii) cyclohexanol and phenol.
(iv) propan-2-ol and 2-methylpropan-2-ol.
(v) phenol and anisole
(vi) ethanol and diethyl ether

5) An alcohol A (C4H10O) on oxidation with acidified potassium dichromate gives carboxylic acid B (C4H8O2). Compound A when dehydrated with conc. H2SO4 at 443 K gives compound C. Treatment of C with aqueous H2SO4 gives compound D (C4H10O) which is an isomer of A. Compound D is resistant to oxidation but compound A can be easily oxidised. Identify A, B, C and D and write their structures.

ALDEHYDES,KETONES AND CARBOXYLIC ACIDS

1 ) Write equations for the following named reactions:

a) Nucleophillic addition reaction.
b) clemensen reduction.
c) wolf kishner reduction.
d) aldol condensation.
e) crossed aldol condensation
f) cannizaro reaction.
g) Rosenmund’s reduction.
h) kolbe’s electrolysis
i) Stephen reaction.
j) Etard reaction.
k) decarboxylation.
l) acylation.
m) schotten baumann reaction.
n) Friediel craft’s acylation.
o) esterification.
p) Gattermann- Koch reaction.
q) Hell Volhard Zelensky reaction.

2) Explain

a) Fehling’s test
b) Tollen’s reagent test with suitable examples

3) account for the following:

a) Aldehyde and ketone are polar in nature.
b) Aldehyde and ketones have higher boiling point than hydro carbons of comparable molar mass.
c) Aldehyde and ketones have lower boiling point than alcohols of comparable molar mass.
d) Ketone has higher boiling point than aldehyde of comparable molar mass.
e) Oxidation of primary alcohol to aldehyde is carried out using PCC as an oxidizing agent.
f) Rosenmund’s reduction of acid chloride to aldehyde is carried out using quinoline and sulphur.
g) Aldehyde is more reactive than ketone towards nucleophile.
h) Butanone is less reactive than propanone.

4) How is :

a) HCHO
b) CH3CHO
c) C6H5CHO prepared commercially? Mention two uses of each.

5) Arrange the following in the increasing order of property mentioned:

a) Acetaldehyde, Acetone, Di-tert-butyl ketone, Methyl tert-butyl ketone( reactivity with HCN)
b) 2-Bromo butanoic acid, 3-Bromo butanoic acid, Butanoic acid, 3-Methyl propanoic acid (acid strength)
c) Benzoic acid, 4-Nitro benzoic acid, 3,4-Dinitro benzoic acid, 4-Methoxy benzoic acid (acid strength)
d) Ethanal, Propanal, Propanone, Butanone( increasing order of reactivity towards nucleophile)
e) Benzaldehyde, p-Tolualdehyde, p-Nitro benzaldehyde, Acetophenone(increasing order of reactivity towards nucleophile)
f) Butanal, Butanol, Ethoxy ethane and Butane (increasing order of boilimg point)

ORGANIC COMPOUNDS CONTAINING NITROGEN

1) Giving an example of each, describe the following reactions :

(i) Hoffman bromamide reaction
(ii) Gabriel phthanlimide synthesis
(iii) Gatterman reaction
(iv) Coupling reaction
(vi) Carbylamine reaction
(vii) Acetylation of aniline.

2) How will you bring about the following conversions?

(i) benzene to Aniline
(ii) aniline to benzene
(iii) ethanoic acid to ethanamine
(iv) p-toluidine to 2-bromo-4-methylaniline.
(v) methylbromide to ethanamine

3) Give one chemical test to distinguish between the following pairs of compounds :

(i) methylamine and dimethylamine
(ii) secondary and tertiary amines
(iii) ethylamine and aniline
(iv) aniline and benzylamine
(v) methylamine and methanol
(vi) methylamine and N, N-dimethylamine
(vii) ethanol and ethanamine.

4) Explain why :

(i) The C–N–C bond angle in trimethyl amine is 108°
(ii) the quaternary ammonium salts having four different alkyl groups are optically active
(iii) alkylamines are more basic than ammonia
(iv) aniline cannot be prepared by Gabriel phthalimide synthesis
(v) Garbriel phthalimide synthesis is preferably used for synthesising primary amines.
(vi) ethylamine is soluble in water but aniline is not

5) Three isomeric amines A, B and C have the molecular formula C3H9N. Compound A on reaction with benzene sulphonyl chloride forms a product which is soluble in NaOH. Compound B on reaction with benzene sulphonyl chloride forms a product which is insoluble in NaOH and compound C does not react with benzene sulphonyl chloride. Identify A, B and C.

BIOMOLECULES

1) Name four type of intermolecular forces which stabilize 2° and 3° structure of proteins.

2) Explain what is meant by :
(i) a peptide linkage
(ii) a glycosidic linkage?

3) Give the sources of vitamin A and E and name the deficiency diseases resulting from lack of vitamin A and E in the diet.

4) Name the two components of starch? Which one is water soluble?

5) (i)Acetylation of glucose with acetic anhydride gives glucose pentaacetate. Write the structure of the pentaacetate.
(ii)Explain why glucose pentaacetate does not react with hydroxylamine?

POLYMERS

1) What do you mean by vulcanization of natural rubber? What is the purpose of vulcanization?

2) Explain the mechanism of polymerization of ethene.

3) What are

a) natural polymers
b) semi synthetic polymers
c) synthetic polymers? Give one example each.

4) Arrange the following in the increasing order of molecular forces:

a) Nylon 66
b) polythene
c) Buna-S-rubber

5) What do you mean by addition and condensation polymers? Give 2 examples each.

CHEMISTRY IN EVERY DAY LIFE

1) What are antacids? Give two examples.

2) Ranitidine and cimitidine are better antacids than metal hydroxides and hydrogen carbonates. Why?

3) Give one important use of each of the following:

i) terfenadine
ii) chlordiazepoxide
iii) Morphine
iv) dysidazirine
v) Norethindrone.

4) Why does soap not work in hard water?

5) What are tranquilisers? Give two examples.

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