ADDITIONAL QUESTIONS – THREE MARK

1. Write the uses of Fluorine
1. Fluorine is used in the manufacture of freons. These non-toxic, non-combustible and volatile liquids are used as refrigerants in refrigerators, deep freezers and air conditioners.

2. CaF2 is used as flux in metallurgy.

3. NaF is used as a preservative to prevent fermentation and also for preventing dental cavities.

4. SF6 is used as an insulating material in high voltage equipment.

5. Teflon is used as container to store hydrofluoric acid.

6. UF6 is used in the separation of U235 from U238.

2. How is Lunar caustic prepared?

Lunar caustic (Silver nitrate) is prepared by dissolving silver in dilute nitric acid.

3Ag + 4HNO3 → 3AgNO3 + 2H2O + NO↑

3. What is binding energy of Nucleus?

Whenever a nucleus is formed, certain mass is converted into energy. Hence for atom, the atomic mass is lower than the sum of masses of protons, neutrons and electrons present. The difference in mass is termed as “mass defect”. This is the measure of the binding energy of proton and neutron in the nucleus. The relationship between mass - energy is explained by Einstein equation ΔE = Δm . C2

4. Degree of dissociation of PCl5 at 1 atm and 25°C is 0.2. Calculate the Kp value for equilibrium PCl5 ⇌ PCl3+ Cl2 at 25°C.

Total pressure, P = 1 atm

Degree of dissociation, x = 0.2

Kp = ?

For PCl5 dissociation equilibrium,

Kp = x2P / 1 – x2

Kp = (0.2)2 (1.0) / 1 – (0.2)2

      = 0.04 / 1 – 0.04

      = 0.04 / 0.96

Kp = 0.042 atm

5. Give three examples for first order reaction.

Examples for first order reaction

1. All radioactive transformations follow first order kinetics.

92U238 → 90Th234 + 2He4

2. Decomposition of sulphuryl chloride in the gas phase

SO2Cl2(g) → SO2(g) + Cl2(g)

3. Inversion of sucrose in acidic aqueous.

                             H+

C12H22O11 + H2O → C6H12O6 + C6H12O6

4. Decomposition of nitrogen pentoxide in CCl4.

N2O5 → 2NO2 + ½ O2

5. Decomposition of H2O2 in aqueous solution

         Pt

H2O2 → H2O + ½O2

6. Define colloidal solution.

When the diameter of the particles of a substance dispersed in a solvent ranges from about 10A° to 2000A°, the system is termed a colloidal solution.

7. How is formic acid obtained from glycerol?

At 383 K, Glycerol reacts with Oxalic acid to give glyceryl monooxalate which eliminates one molecule of carbon dioxide forming glycerol mono formate.

Glycerol mono formate on hydrolysis gives formic acid. In this reaction glycerol acts as a catalyst.

8. What happens when Benzaldehyde is heated with concentrated NaOH?

Benzaldehyde undergoes Cannizaro reaction because of the absence a-hydrogen.

It involves self oxidation and reduction of benzaldehyde when heated with concentrated NaOH.

When Benzaldehyde is heated with concentrated NaOH, it gives Sodium benzoate and  Benzyl alcohol.

                                         NaOH

C6H5CHO + C6H5CHO     →   C6H5COONa + C6H5CH2OH

9. An organic compound ‘A’ C7H7NO when treated with Br2 /alkali gives ‘B’ C6H7N. “B” undergoes diazotisation reaction. Identify ‘A’ & ‘B’.

                                   Br2 / KOH

C6H5CONH2        →         C6H5NH2   +  CO2   (Hoffman’s bromamide reaction)

(A) Benzamide                   (B) Aniline

                                            HCl

C6H5NH2   +  O=N–OH       →       C6H5 – N = N – Cl    (Diazotisation reaction)

(B) Aniline                          273 K      Benzene diazonium chloride              

Compound A C7H7NO	Compound B C6H7N
C6H5CONH2	C6H5NH2
Benzamide	Aniline

10. Determine the average life of U238 having t1/2 = 140 days.

           Half-life, t½ = 140 days

          Average life, τ (Tau) = ?

t½ = 0.693 / λ

t½ = 0.693 x τ                               Since, Average life, τ (Tau) = 1 / λ

               τ  = t½ / 0.693   = 140 / 0.693

                       Average life = 202.02 days

Or

       Average life, τ (Tau) = 1.44 t½

                                     = 1.44 x 140 days

                                     = 201.6 days

11. Evaluate / Calculate the entropy change for the following process possessing ∆H(Transition) = 2090 J.mol–1.

       1 mole Sn (α, 13oC) ⇌ 1 mole Sn (β, 13oC)

Ttransition = 13 + 273 = 286 K.

     ∆Strans = ∆Htrans / Ttrans (K)

                              = 2090 J.mol–1 /  286K

     ∆Strans = 7.307 J.K–1.mol–1

12. What is glycerose? How is it prepared from glycerol?

“Glycerose” is a mixture of glyceraldehyde and dihydroxy acetone.

Milder oxidising agents like bromine water or Fenton’s reagent [FeSO4 + H2O2] or sodium hypobromite – oxidises glycerol to glycerose.

 

13. Give the IUPAC names for the following: a) Crotonaldehyde b) Methyl n–propyl ketone c) Phenyl acetaldehyde.

Common names                     IUPAC names

a) Crotonaldehyde                  – 2–Butenal

b) Methyl n-propyl ketone      – 2–Pentanone

c) Benzaldehyde                     – Phenyl methanal

14. An organic compound (A) of molecular formula C2H5NO reacts with Br2 / NaOH to give compound (B) of molecular formula (CH5N). (A) is reduced by LiAlH4 to give compound (C) of formula (C2H7N).  Identify (A), (B) and (C).

                                   Br2 / KOH

CH3CONH2        →         CH3NH2    +   CO2    (Hoffman’s bromamide reaction)

(A) Acetamide                   (B) Methyl amine

                                                  LiAlH4

CH3CONH2  +  4 [H]     →         CH3CH2NH2

(A) Acetamide                              (C) Ethyl amine

Compound A C2H5NO	Compound B CH5N	Compound C C2H7N
CH3CONH2	CH3NH2	CH3CH2NH2
Acetamide	Methylamine	Ethyl amine

15. What are antipyretics? Give an example.

Antipyretics are the compounds used for the purpose of reducing fever (lowering the body temperature to the normal).

Examples:

Aspirin, Antipyrine, Phenacetin and Paracetamol

16. The Eectron affinities of Beryllium (z = 4) Magnesium (z = 12) and Calcium (z = 20) are almost zero. Why?

It is due to the Extra stability of the completely filled 2s–orbital in Beryllium, completely filled 3s–orbital in Magnesium and completely filled 4s–orbital in Calcium. As these are stable electronic configurations, they do not have / are having least tendency to accept electrons.

17. What is the action of heat on silver nitrate?

On heating AgNO3 decomposes in two stages

               723 K

2AgNO3    →   2AgNO2 + O2

               980 K  Silver nitrite

AgNO2 → Ag + NO2

18. For the equilibrium 2NOCl(g) ⇌ 2NO(g) + Cl2(g) the value of the equilibrium constant Kc is 3.75 x 10–6 at 790°C. Calculate Kp for this equilibrium at the same temperature. (R = 0.0821 dm3 atm K–1 mol–1)

The equilibrium: 2NOCl(g) ⇌ 2NO(g) + Cl2(g)

Equilibrium constant, Kc = 3.75 x 10–6

R = 0.0821 dm3 atm K–1 mol–1

Temperature, T = 790°C = (273 + 790) K = 1063 K

Equilibrium constant, Kp = ?

∆ng = np – nr = (2 + 1) – 2 = 3 – 2 = 1

Kp = Kc(RT)∆n_g

Kp = 3.75 x 10–6 x (0.0821 x 1063)1

      = 3.75 x 87.27 x 10–6

      = 327.3 x 10–6

Kp = 3.273 x 10–4

19. Define half life period.

Half life period, ‘t½’, of a reaction is defined as the time required to reduce the concentration of a reactant to one half of its initial value.

20. Write any two characteristics of first order reaction.

1.  When the concentration of the reactant is increased by ‘n’ times, the rate of reaction is also increased by n times. That is, if the concentration of the reactant is doubled, the rate is doubled.

2. The unit of rate constant of a first order reaction is sec–1 or time–1.

k1 = rate / (a - x ) = mol.lit –1sec / mol.lit–1 = sec–1

3. The time required to complete a definite fraction of reaction is independent of the initial concentration of the reactant.

21. What is ionic product of water? Give its value.

The product of concentrations of hydronium (H3O+) and hydroxide (OH–) ions.

[H3O+] [OH–] = Kw

At 298 K, Kw = 1 ´ 10–14 mol2.dm–6

22. How does acetone reacts with chloroform in the presence of KOH?

With chloroform acetone forms an addition product – Chloretone.

          CH3                             CH3

           |                 KOH            |

CH3 – C + H–CCl3  → CH3 – C – CCl3 (Chloretone)

          ||                                      |

          O                                   OH

23. Write any three uses of lactic acid.

Uses of lactic acid :

1. In tanning industry.

2. In soft drinks.

3. In the treatment of digestive disorder in children.

4. Preparation of lactates, ethyl lactate as a solvent.

5. Silver lactate as an antiseptic and astringent.

24. Identify A, B and C.

Benzylamine reacts with Nitrous acid to give Benzyl alcohol (A).

C6H5CH2NH2 + O = N- OH → C6H5CH2OH +  N2 + H2O

                                                               (A)

Benzylamine reacts with Acetyl chloride N-benzyl acetamide (B) is formed.

C6H5CH2NH2 + ClCOCH3 → C6H5CH2NHCOCH3 +  HCl

                                                               (B)

Benzylamine on oxidation with Potassium permanganate the side chain with the amino group is oxidised to give Benzoic acid (C).

Compound A	Compound B	Compound C
C6H5CH2OH	C6H5CH2NHCOCH3	C6H5COOH
Benzyl alcohol	N-benzyl acetamide	Benzoic acid

25. What are antibiotics? Give one example.

Many microorganisms (bacteria, fungi and moulds) produce certain chemicals which inhibit the growth or metabolism of some other microorganism. Such chemical compounds are known as antibiotics.

These need be present only in low concentration to be effective in their antibiotic action.

Exampe:

Penicillin (The first antibiotic, discovered by Alexander Fleming in1929, from mould Penicillium notatum)

26. Give one gaseous equilibrium reaction as an example for the following : i) ∆n_g = 0 ii) ∆n_g = + ve

i) ∆n_g = 0

H2(g) + I2(g) ⇌ 2HI(g)

ii) ∆n_g = + ve

2H2O(g) + 2Cl2(g) ⇌ 4HCl(g) + O2(g)

27. How is Delta formed?

Formation of delta : River water is colloidal solution of clay. Sea water contains a number of electrolytes. When river water meets the sea water, the electrolytes present in sea water coagulate the colloidal solution of clay which get deposited with the formation of delta.

Colloidal solution (Sol) + Electrolyte (Coagulating agent) → Precipitate

                HNO2          Sn/HCl          CS2

28. CH4  ----->   A  ------>   B  ---->   C. Identify A, B and C.

               400oC                                HgCl2   

Compound A	Compound B	Compound C
CH3NO2	CH3NH2	CH3– N = C = S
Nitro methane	Methyl amine	Methyl isothiocyanate

         

THREE MARK Qs : S–12 [1 - 9] M–13 [10 – 15] J–13 [16 – 25] S – 13 [26 – 28]