ADDITIONAL QUESTIONS 2014 – 3 MARK

1. Calculate the entropy increase in the evaporation of 1 mole of a liquid when it boils at 100°C having heat of vaporisation at 100°C as 540 cals / gm.

ΔHvap = 540 cals / gm = 540 x 18 cals / mol = 9720 cals / mol

Tb (K) = 273 + 100 = 373 K

ΔSvap = ?

ΔSvap = ΔHvap / Tb (K)

      = 9720 cals / mol / 373 K

      ΔSvap = 26.06 cal.mole–1K–1

2. What are consecutive reactions? Give an example.

The reactions in which the reactant forms an intermediate and the intermediate forms the product in one or many subsequent reactions are called as consecutive or sequential reactions. In such reactions the product is not formed directly from the reactant. Various steps in the consecutive reaction are shown as below:

    k1     k2

A → B  → C

A = reactant; B = intermediate; C = product.

Initially only the reactant A will be present. As the reaction starts, A produces an intermediate B through k1 rate constant. As and when B is formed, it produces the product C through k2 rate constant. After the completion of reaction only ‘C’ is present and concentrations of A and B will be zero.

Example: Saponification of a diester in presence of an alkali

                                          k1                                         k2

R’OOC– (CH2)n–COOR → R’OOC–(CH2)n–COOH → HOOC – (CH2)n – COOH

3. Define ‘‘Racemisation’’.

When equal amounts / 1:1 ratio of (+) or dextrorotatory or d-isomer and (–) or laevorotatory or l-isomer are mixed we get a ‘‘racemic mixture’’ or (±) – mixture or dl – mixture and this process is called racemisation.

4. Give the Victor Meyers Test for tert-butyl alcohol.

Absence of α–H in tertiary alcohol makes it inactive to nitrous acid

5. What is picric acid? How is it prepared from phenol?

2, 4, 6 – Trinitro phenol is called as picric acid.

Reaction of phenol with nitrating mixture – conc. H2SO4 and conc. HNO3 mixture – gives Picric acid.

6. An aromatic Primary amine A with molecular formula C6H7N undergoes diazotization to give B. When the aqueous solution of B is boiled it gives compound C. Identify the compounds A, B and C.

Since (A) undergoes diazotization, (A) may be a Nuclear aromatic amine. Comparing with molecular formula (A) may be Aniline.

C6H5NH2 + NaNO2 + HCl    →     C6H5N = N – Cl (Diazotisation)

 (A) Aniline                          273K      (B) Benzene diazonium chloride

C6H5N = N – Cl  + H2O → C6H5OH + N2 + HCl

(B)                                           (C) Phenol

Compound A	Compound B	Compound C
C6H5NH2	C6H5N = N – Cl	C6H5OH
Aniline	Benzene diazonium chloride	Phenol

7. In what way antacids are important? Give an example.

After eating oily and spicy food the burning sensation in stomach / food pipe is due to the imbalance in the acidity in the stomach. Antacids contain magnesium and aluminium hydroxides, in addition to flavouring agents and colour which provides relief from such burning sensation.

Example: Milk of Magnesia

8. What is burnt alum?

When heated, Potash alum melts at 365K and on further heating loses the whole of its water of crystallisation and swells up. The swollen mass so produced is called burnt alum.

9. The half life of Th233 is 1.4 × 1010 years. Calculate its disintegration constant.

        Half-life t½ = 1.4 × 1010 years

      Disintegration constant λ = ?

         t½ = 0.693 / λ

                       λ = 0.693 / t½

                          = 0.693 / 1.4 × 1010

                       λ = 4.95 × 1011 years–1

Or                                    λ = 1.57 x 10 –18 sec–1

10. Give the three uses of superconductors.

1. It is a basis of new generation of energy saving power systems. Super conducting generators are smaller in size and weight when we compare with conventional generators. These generators consume very low energy and so we can save more energy.

2. High efficiency ore separating machines may be built using superconducting magnets.

3. Superconducting solenoids are used in Nuclear Magnetic Resonance Imaging equipment which is a whole body scan equipment.

11. Write the equilibrium constant for the following

i) H2O2(g) ⇌ H2O(g) + ½O2(g)

ii) CO(g) + H2O(g) ⇌ CO2(g) + H2(g)

iii) N2O4(g) ⇌ 2NO2(g)

i) Kc = [H2O] [O2]1/2 / [H2O2]                    K_p = p_H2O . p½_O2 / p_H2O2

ii) Kc = [CO2] [H2] / [CO] [H2O]                 K_p = p_CO2 . p_H2 / p_CO . p_H2O                           

iii) K_c = [NO2]2 / [N2O4]                              K_p = p2_NO2 / p_N2O4

12. Give the IUPAC name of the following

(a) HOOC – COOH (b) CH3COOH (c) HOOC (CH2)4 COOH

Formula                                 IUPAC name

(a) HOOC – COOH               Ethane dioic acid

(b) CH3COOH                       Ethanoic acid

(c) HOOC (CH2)4 COOH      Hexane dioic acid

13. Identify A, B and C.

              CHCl3          H2 / Pt

CH5 N       →      B        →      C. Identify A, B and C.

              KOH

CH3NH2 + CHCl3 + 3KOH → CH3NC + 3KCl + 3H2O (Carbylamine reaction)

 (A)             Chloroform               (B) Methyl isocyanide

                      H2 / Pt

CH3NC      →      CH3NHCH3

(B) Methyl isocyanide  (C) Dimethylamine

Compound A	Compound B	Compound C
CH3NH2	CH3NC	CH3NHCH3
Methyl amine	Methyl isocyanide	Dimethylamine

14. Why most of the transition metals and their compounds are used as catalyst?

The catalytic activity of transition metals is due to the following reasons.

i) They show a variety of oxidation states and thereby can form intermediate products with various reactants.

ii) They are also capable of forming interstitial compounds which can adsorb and activate the reacting species.

15. What is Spallation reaction? Give an example.

The reactions in which high speed projectiles may chip a heavy nucleus into several fragments.

29Cu63 + 2He4 + 400 MeV →17Cl37 + 14 1H1 + 16 0n1

16. Calculate Δng, for the following reactions

(a) N2(g) + 3H2(g) ⇌ 2NH3(g)

(b) N2O4(g) ⇌ 2NO2(g)

(c) PCl5(g) ⇌  PCl3(g) + Cl2(g)

(a) N2(g) + 3H2(g) ⇌ 2NH3(g)

Δng = np(g) – nr(g)

        = 2 – (1 + 3)

        = 2 – 4

        = –2

(b) N2O4(g) ⇌ 2NO2(g)

Δng = np(g) – nr(g)

        = 2 – 1

        = 1

 (c) PCl5(g) ⇌  PCl3(g) + Cl2(g)

Δng = np(g) – nr(g)

        = (1 + 1) – 1

        = 2 – 1

        = 1

17. Give the tests for phenol.

1. Neutral ferric chloride Test: Phenol gives violet colour with neutral ferric chloride.

2. Halogenation: When phenol is treated with bromine water the colour of bromine disappears with the formation of white precipitate. The white precipitate consists of 2, 4, 6-tribromo phenol.

3. Dye test: Phenol couples with benzene diazonium chloride in alkaline medium to form p-hydroxy azobenzene, a red orange dye.

 

4. Phthalein fusion: Phenols are heated with phthalic anhydride and con. H2SO4 to give Phenolphthalein. This can be tested by the formation of pink colour when it is treated with sodium hydroxide.

18. What happens when the vapours of tert. butyl alcohol is passed over heated Cu at 573 K?

When the vapours of tert. butyl alcohol is passed over heated Cu at 573 K leads to only dehydration to Isobutylene (Absence of a-hydrogen in tert. butyl alcohol)

19. Write the formula of hexamethylene tetramine and draw its structure.

Formula of hexamethylene tetramine (CH2)6N4

Structure:

20. How is chloropicrin prepared? What is its use?

Nitromethane reacts with chlorine in presence of alkali to form chloropicrin, CCl3NO2.

                               NaOH

CH3NO2 + 3Cl2      →         CCl3 NO2 + 3HCl

                                               Chloro picrin (Trichloro nitro methane)

Chloropicrin is used as soil sterilizing agent.

21. Define chemotherapy.

Treatment of certain diseases by destroying the invading organism without damaging the cells of the host, by the use of certain organic compounds in known as chemotherapy.

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