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II IIT-JEE Achiever (Integ.) 2011-13 / Chemistry / Soln. to PU Unit Test - 01 1

H3C CH CH CH

3

CH3 CH3

CH3

CH3CH

2CH

2Cl CH

3CH CH

2H

3C CH CH

3

alc KOH HBr

Br

Na/etherH

3C CH CH CH

3

CH3

CHEMISTRY

Test date 12-05-2012

Class II IIT-JEE Achiever (Integrated) 2011-13

Solution to PU Unit Test - 01

PART - A

I. Questions carrying ONE mark each [5 1 = 5]

1. State Faradays first law of electrolysis.

Ans

During electrolysis, amount of substance deposited at the electrode is directly proportional to quantity of

electricity passed through the electrolyte.

2. What are enantiomers?

Ans

Enantiomers are the pair of optical isomers that are non-superimposable mirror images of each other.

3. Name the reagent employed to convert bromoethane to ethane.

Ans

Alcoholic KOH.

4. DCBClCHCHCH ether/NaHBrKOHalc223

What is the product D in the above reaction?

Ans 2,3-dimethylbutane or

5. What is the pH of 102 M NaOH?

Solution

[OH] = 10

2

pOH = 2 pH + pOH = 14

pH = 12

PART - B

II. Questions carrying TWO marks each (answer any five) [5 2 = 10]

6. When same amount of electricity is passed through solution of CuSO4 and HCl, 32 mg of copper is

obtained in first case. Calculate the volume of hydrogen liberated in the second case.

Ans

hydrogenofmass.Eq

copperofmass.Eq

hydrogenofmass

Cuofmass=

mass of hydrogen = g1032

1g1032 33

=

volume of hydrogen at STP = 3333

dm102.11dm

2

104.22

=

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7. A weak monoacid base has a pH of 10 at a concentration of 0.01 M. What is percentage ionization of the

base?

Ans

pH = 10 pOH = 4 [OH] = 10

4M = c

%11001010

c]OH[ 2

4

===

8. Write the equation for rate determining step in the mechanism of hydrolysis of tertiary butyl bromide.

Ans

( ) ( ) +

+ BrCCHCBrCHnCarbocatio

33

slow

33 [1 mark]

Rate eq. rate = k[(CH3)3 CBr] [1 mark]

9. Name the reagents used to convert a haloalkane into

(a) an alcohol

(b) alkanenitrile

Ans

(a) aq KOH [1] (b) alc KCN [1]

10.Arrange the following carbocations in the order of their stability and give reason.

(i) ter-butyl carbocation (ii) isopropyl carbocation (iii) ethyl carbocation

Ans

(i) > (ii) > (iii) [1]

+I effect of CH3 groups [1]

11.Give two limitations of Arrhenius theory of electrolytic dissociation.

Ans

(i) Arrhenius theory fails to account for the conductivity of electrolytes in fused state. [1]

(ii) It ignores the inter-ionic force of attraction in electrolyte solutions. [1]

PART - C

III. Questions carrying FIVE marks each (answer any six) [6 5 = 30]

12. (a) Show that pH + pOH = 14 at 298 K.(b) Calculate hydrogen and hydroxyl ion concentration in a solution of pH 1.7. [3 + 2]

Ans

(a) [H+][OH

] = 10

14at 298 K

Taking log and reversal of sign

log[H+] log[OH

] = 14 , pH + pOH = 14

(b) pH = 1.7

[H+] = antilog (1.7) = 0.02 M

[OH] = M105

02.0

10 1314

=

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CH3 CH CH2 + HI CH3 CH CH3

I

HO C Br

H

HH

HO C H + Br

H

H

HO + H C Br

H

H

13. (a) What are the two conditions for an organic compound to show geometrical isomerism?

(b) How are the following prepared?

(i) Bromoethane from ethanol

(ii) Propanenitrile from bromoethane

(iii) 2-iodopropane from propeneAns

(a) (i) Restricted rotation around carbon-carbon double bond or carbon-carbon single bond. [1 mark]

(ii) Two groups attached to the carbon must be different. [1 mark]

(b) (i) 3352352 POHBrHC3PBrOHHC3 ++ [1 mark]

(ii) KBrNCHCKCNBrHC 52.)alc(

52 + + [1 mark]

(iii) [1 mark]

14.What is SN2

mechanism? Explain it using hydrolysis of methyl bromide. [2 + 3]

AnsSN

2: Bimolecular nucleophilic substitution single step / strong nucleophile. [1 mark]

Mechanism:

[4 marks]

Inverted configuration.

Walden inversion.

15. (a) What is SN1 mechanism? Explain using hydrolysis of 3 butyl chloride.(b) What is racemic mixture? Give one example. [3 + 2]

Solution

(a) Two step / unimolecular / r = k [RX]

(i)+ + XRXR

Slow

(ii) oductPrfast

ncarbocatioNuRNuR +

+

[1 3]

(b) Equal amount of d and l enantiomers.

Inactivity due to external compensation

Eg: lactic () acid. [2]

16. (a) Trichloro acetic acid is a stronger acid than acetic acid. Give reason.

(b) Give two differences between electromeric and inductive effect.

(c) Give an example of a group having M effect. [2 + 2 + 1]

Solution

(a) Cl exerts I effect [1]

Greater the I effect, stronger the acid [1]

(b) Two differences [2]

(c) One example [1]

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* * *

17. (a) A weak acid HA dissociates to an extent of 4.3 % in a 103 M solution of it. Calculate its dissociation

constant? [2]

(b) Define specific conductance. How is it related to molar conductance? [2]

(c) Account for the fact that NH3 acts both as a Lewis base and as a Bronsted base. [1]

Solution

(a)C

k

C

k a2a ==

32

2a 10

100

3.4Ck

== [1]

= 1.849 106

[1]

(b) It is the conductance of ions present in one meter cube of an electrolyte solution placed between two

electrodes of one meter apart. [1]

c

m10cork

33== [1]

(c) Ammonia donates an electron pair Lewis base []

Ammonia accepts a proton Bronsted base []

18. (a) Give any four assumptions of Arrhenius theory of electrolytic dissociation. [4]

(b) What is the [H+] ions in 0.1 M formic acid which is 4.2 % dissociated. [1]

Solution

(a) Refer Module 2, page 33.

(b) [H+] = c

= 3102.4100

2.41.0 = mol dm

3

19. (a) 8g of NaOH is present in 10 dm3 of the solution. Calculate the pH of the solution? [2]

(b) Derive Ostwalds dilution law for a weak electrolyte. [2]

(c) Why AlCl3 is a Lewis acid? [1]

Solution

(a) Mass per 1000 cm3

of NaOH = 0.8 g

Normality = 02.040

8.0

E

W== []

[OH] = 0.02 mol dm

3 []

pOH = log10[OH] = log10[0.02] []

= 1.6990

pH = 14 pOH = 14 1.6990 = 12.3010 []

(b) Refer Module 2, page 41.

Assumption [1] Final equation,)1(

ck

2

a

= []

(c) It accepts an electron pair or it is electron deficit. [1]

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