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GOVERNMENT OF KARNATAKA

KARNATAKA STATE PRE – UNIVERSITY EDUCATION EXAMINATION BOARD

II YEAR PUC SUPPLEMENTARY EXAMINATIONJUNE – 2019

SCHEME OF VALUATION Subject Code: 34 Subject: chemistry

Q. No. Part – A Marks

I. Answer all the questions. Each question carries 1 mark. 10 1 = 10

1) Write the unit of molality of a solution

Ans. mol kg–1 or mol/kg 1

2) At a given temperature, oxygen gas is more soluble in water than Nitrogen

gas. Which one of them has higher value of KH?

Ans. N2 or Nitrogen 1

3) State Faraday's first law of electrolysis.

Ans. The amount of substance discharged at any electrode during electrolysis is

proportional to the quantity of electricity passed through the electrolyte.

1

4) Give an example for pseudo first order reaction.

Ans. Inversion of cane sugar OR C12 H22O11 + H2O C6H12O6+ C6H12O6

OR Acid hydrolysis of an ester OR

3 3 2 3 3

dil HCl or

HCH COOCH H O CH COOH CH OH

Any suitable example.

1

5) Enthalpy of physical adsorption is quite low: Give reason.

Ans. Because it involves weak van der Waals’ forces. 1

6) Name the method used for concentration of sulphide ores.

Ans. Froth Floatation Method or Process. 1

7) Among Noble gases which one is most abundant in air?

Ans. Ar or Argon 1

8) Name the major organic product formed when 2-bromopentane is heated

with alcoholic potassium hydroxide solution.

Ans. Pent – 2 – ene or 2 – Pentene 1

9)

Name the above reaction.

Ans. Gatterman – Koch reaction. 1

10) Name the Hormone which regulates blood sugar level.

Ans. Insulin or Glucagon. 1

Part – B

II. Answer any FIVE of the following. Each question carries two marks. 5 2 = 10

11) Which type of extrinsic semiconductor is formed when silicon is doped with phosphorus? Mention the major charge carrier in it.

Ans. n – type, Electron(s). 1 + 1

12) Draw a neat labeled diagram of Standard Hydrogen Electrode (SHE). Write its Half- Cell reaction.

2

Ans.

H+(aq) + e— ⇄ ½H2(g)

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13) Name any two factors affecting the rate of a reaction.

Ans. (i) Concentration of the reactants (ii) Temperature of the reactants (iii) Nature of the reacting substances (iv) Presence of catalyst (v) Intensity of light. (Any two)

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14) a) Zr and Hf have almost identical radii: Give reason.

b) Name the gas liberated when Lanthanoids (Ln) react with acids.

Ans. a) Due to Lanthanoid contraction.

b) Hydrogen gas or H2 gas

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15) How does phenol react with conc.HNO3? Give equation.

Ans. When phenol is heated with concentrated nitric acid, 2, 4, 6-trinitrophenol (picric acid) is formed.

OR Self-explanatory equation.

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16) Explain Cannizzaro reaction with an example.

Ans. Aldehydes with no - hydrogen atom when treated with concentrated alkali (NaOH or KOH), undergo self-oxidation and reduction (disproportionation) to give carboxylic acid salt and alcohol. This is called Cannizzaro’s reaction. 2HCHO + Conc.KOH HCOOK + CH3OH OR C6H5CHO + Conc.NaOH C6H5COONa + C6H5CH2OH OR Self-explanatory equation.

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17) What is the role of the following chemicals infood?

a) Sodiumbenzoate.

b) Saccharin.

Ans. a) Food preservative.

b) Artificial sweetening agent.

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18) What is saponification? Write the equation to get sodium stearate by this method.

Ans. When oil or fat is heated with aqueous NaOH, sodium salts of fatty acids

(soaps) are formed.

1 + 1

3

Part – C

III. Answer any five of the following. Each question carries 3 marks: 5 3 = 15

19) In the extraction of Aluminium by Hall- Herault process:

a) Write the neat labeled diagram of electrolytic cell.

b) Give the equation of overall cell reaction.

c) What is the role of cryolite?

Ans. a)

.

b) 2 3 22Al O 3C 4Al 3CO

c) It lowers the melting point of the electrolyte (mix) and brings conductivity. Or acts as an electrolyte.

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20) For the manufacture of Ammonia by Haber's process, write the flow chart and chemical equation with suitable conditions.

Ans.

2 3 2

2( ) 2( ) 3( )

|

700 , 2003 2g g g

Iron oxide Al O K O

K atmN H NH

ˆ ˆ ˆ ˆ ˆ ˆ ˆ ˆ ˆ ˆ ˆ†‡ ˆ ˆ ˆ ˆ ˆ ˆ ˆ ˆ ˆ ˆˆ

OR

N2(g) + 3H2(g) 2NH3(g); o 1

f H 46 1 kJ mol

According to the Lechatelier’s principle, High pressure of 200atm and temperature of 700K

Finely divided Iron oxide catalyst and promoter K2O and Al2O3.

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2

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4

21) Complete the following equations:

a) 4AI +3O2

b) PbS(s) +4O3(g)

c) C +2H2SO4

(conc.)

Ans. a) 2Al2O3

b) PbSO4+ 4O2

c) 2H2O + CO2 + 2SO2

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22) a) Give any two reasons for anomalous behavior of Fluorine.

b) Write the structure of perchloric acid (HClO4).

Ans. a) (i) Ionization enthalpy, electro negativity and electrode potentials are all higher

for fluorine than others. (ii) Hydrogen fluoride is a liquid due to strong hydrogen bonding. Other hydrogen

halides are gases. (iii) Ionic and covalent radii, m. p. and b. p., enthalpy of bond dissociation and

electron gain enthalpy are quite lower than expected. (Any two) b)

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23) a) Calculate the spin only magnetic moment of Ti3+ ion (Atomic number of

Ti =22).

b) Cu2+salt solutions are coloured: Give reason.

Ans. 1

3 1.73

( ) ( 2)

1(1 2)

n

BM

a n n

b) Due to the presence of unpaired electron or due to d – d transition of

electrons.

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24) Write the balanced equations involved in the preparation of potassium dichromate(K2Cr2O7) from chromite ore.

Ans. 4 FeCr2O4 + 8 Na2CO3 + 7O2 8Na2CrO4 + 2Fe2O3 + 8CO2.

2 4 2 2 7 22Na CrO 2H Na Cr O 2Na H O OR

2 4 2 4 2 2 7 2 4 22Na CrO H SO Na Cr O Na SO H O

2 2 7 2 2 7Na Cr O 2KCl K Cr O 2NaCl

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25) Explain the hybridization, geometry and magnetic property of [Co(NH3)6]3+

ion on the basis of Valance Bond Theory (VBT). [Atomic number of Co = 27].

Ans. E.C. of Co3+ ion is [Ar]3d6 4s0

Under the influence of strong NH3

ligands spin pairing takes place in 3d

orbitals.

d2sp3 hybridization takes place.

[Co (NH3)6]3+ ion.

Octahedral geometry.

Diamagnetic because of the absence

of unpaired electron.

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26) a) For a given complex [Co(NH3)5 NO2]Cl2. Write its IUPAC name and

Linkage isomer. b) Which set of d-orbitals of a metal atom/ion experience more repulsion in

octahedral field created by the ligands?

Ans. a) pentaamminenitrito – N – cobalt(III) chloride.

[Co(NH3)5 (ONO)]Cl2

b) dx2– y2 and dz2 orbitals.

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Part – D

IV. Answer any three of the following. Each question carries five marks. 3 5 = 15

27) (a) Calculate the packing efficiency in Face Centred Cubic (FCC) structure. (b) Write any two differences between Frenkel and Schottkydefects.

Ans. a)

The edge length = ‘a’

Radius of sphere = r

Face diagonal AC = b = 4r

In AC2 = b2 = AB2 + BC2

= a2 + a2 = 2a2

b = a But b = 4r = a

a = = 2 r

Volume of sphere = r3

Volume of cube = a3 = (2 r)3

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Number of particles per unit cell in FCC = Z = 4 spheres.

Packing efficiency = or

Packing efficiency =

= =

= = 74%

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b) Schottky defect Frenkel defect

2

1) It is caused by missing of equal

number of cat ions and anions

from lattice points to maintain

electrical neutrality.

2) Density decreases

3) It is shown by ionic substances in

which the cation and anoin are of

almost similar sizes.

1) The smaller ion (cat ion) is

dislocated from its normal site to

an interstitial site.

2) Density is not changed

3) It is shown by ionic substances in

which there is a large difference

in the size of ions.

(Any two)

28) (a) On dissolving 2.34g of non-electrolyte solute in 40g of benzene, the boiling point of solution was higher than benzene by

0.81K.Kbvalueforbenzeneis2.53Kkgmol- 1. Calculate the molar mass of

solute. [Molar mass of benzene is 78 gmol-1]

(b) i) State Henry'slaw.

ii) How solubility of a gas in liquid changes with increase in temperature?

Ans. a) M2 =

Kb = 2.53Kkgmol-1 w1 = 40g, w2 = 2.34g,

M2 =? = 0.81K

M2 =

= 182.7gmol–1.

b) (i) The partial pressure of the gas in vapor phase is proportional to the

mole fraction of the gas in the solution”. (ii) Decreases.

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29) a) For a given data: E0Mg2+/Mg = –2.37V, E0Cu2+/Cu = +0.34V

Calculate the emf of the cell in which the following reaction takes place. 2 2

(s) (aq) (aq) (s)Mg Cu Mg Cu

(0.0001M) (0.001M) b) State Kohlrausch law of independent migration of ions.

c) Write the overall cell reaction in mercury cell.

Ans. a)

2 2

0 0 0

cell Cu /Cu Mg /MgE E E

0.34 ( 2.37) 2.71V

ECell = E0Cell ─ log at 298K

ECell = 2.71 ─ log

= 2.68V

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b) The limiting molar conductivity of an electrolyte can be represented as the sum of the individual contributions of the anion and cation of the electrolyte.

c) Zn(Hg) + HgO (s) ZnO(s) + Hg(l)

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30) (a) Derive an integrated rate equation for the rate constant of a first-order reaction.

(b) The rate constant of a reaction is doubled when the temperature increased from 400K to 410K. Calculate the activation energy (Ea)

[R = 8.314 JK1 mol1].

Ans. (a) Consider a first order reaction, R P

1

1

1

(b) =

log 2 =

0.301 =

Ea =

= 94517Jmol–1 OR 94.517kJmol–1

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31) a) How is Gold-sol prepared by Bredig's-arc method?

b) What is Homogeneous catalysis? Give an example.

c) How does entropy change (∆S) for adsorption?

Ans a) This process involves dispersion as well as condensation. It is used to prepare sols of metals such as gold, silver, platinum etc.

In this method, electric arc is struck between electrodes of the metal immersed in the dispersion medium containing a little alkali.

The intense heat produced vaporizes the metal which then condenses to form particles of colloidal size. The colloidal particles formed adsorb charges from the solution and get stabilized.

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b) A reaction in which all the reactants and the catalyst are in the same phase is

called homogeneous catalysis. ( )

2( ) 2( ) 3( )2 2gNO

g g gSO O SO

Any suitable example

c) Entropy decreases 0r ∆S = –ve

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V. Answer any FOUR of the following. Each question carries five marks. 4 5 = 20

32) a) Write the equations for the steps involved in SN1 mechanism for the

conversion of tert- butyl bromide to tert-butylalcohol.

b) Explain Friedel –Crafts alkylation for chlorobenzene. Give equation.

c) What is racemic mixture?

Ans. (a) I Step – 1: Formation of Carbocation:

(Slow)

Step 2:Attack of nucleophile:

(Fast)

(b) Explanation

Equation

OR

OR

General equation.

(c) Equimolar mixture of dextrorotatory and laevorotatory isomers of the same compound is called racemic mixture. OR

A mixture containing two enantiomers in equal proportions will have zero optical rotation.

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33) a. Explain the mechanism of acid catalysed dehydration of ethanol to

ethene.

b. Write general equation for preparation of ether by Williamson synthesis.

c. Among alcohols and phenols which one is more acidic?

Ans. a) Step-1: Formation of protonated alcohol.

Step -2: Formation of carbocation.

Step-3: Formation of ethene by elimination of a proton.

b) 1 1R X R ONa R O R NaX

c) Phenol

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34) a) Complete the following equations:

1. Alk. KMnO4

i) RCH2OH

2. H3O+

NaOH/CaO

ii) CH3COONa ∆ b) Explain Aldol condensation reaction for acetaldehyde. Write equation.

c) What is Formalin solution?

Ans. a) (i)RCOOH

(ii)CH4

b) Explanation

Equation

OR

Self-explanatory equation.

2CH3CHO CH3 – CH – CH2 – CHO Ethanal |

OH 3 – Hydroxybutanal

c) 40% aqueous solution of formaldehyde.

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35) a) How does Primary amine undergo carbyl amine reaction? Give chemical

equation.

b) How aniline is prepared by Hoffmann bromamide degradation reaction?

Give equation.

c) Write the general formula of diazonium salt

Ans. a) Explanation

Equation

OR

Self-explanatory equation.

R – NH2 + CHCl3 + 3KOH R – NC + 3KCl + 3H2O

10 – Amine (Alc) Alkyl isocyanide

b) Explanation

Equation

OR

Self-explanatory equation.

C6H5 – CONH2 + Br2 + 4NaOH → C6H5 – NH2 + Na2CO3 + 2NaBr + 2H2O Benzamide Aniline

c) RN2+X– R = Aryl group OR Ar N2+X–

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36) (a) Write the Haworth structure of Maltose. (b) i) Name a naturally occuring ∝-amino acid which is optically inactive.

(ii) How many peptide bonds are present in a tripeptide? (c) Deficiency of which Vitamin causesNight blindness?

Ans. (a) H H

OH

H

H

OHH

H

CH2OH

OH

OH

H

OH

H

H

H

CH2OH

O

Maltose

-D-Glucose unit

O

-D-Glucose unit

O

HO

(b) (i) Glycine

(ii) Two peptide bonds are formed.

(c) Vitamin – A OR ‘A’

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37) a) What is meant by polymerization? Name the monomer used in the

preparation of Polyvinyl Chloride (PVC).

b) Write partial structure of the following polymers.

(i) Polypropene. (ii) Teflon (iii) Neoprene.

Ans. a) The process of formation of polymers from respective monomers.

OR any suitable definition.

Vinyl chloride OR Chloroethene.

b)

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