CHEMISTRY (Theory)
Code No. 56/1/2
Time Allowed: 3 hours] [Maximum Marks: 70
General Instructions:
(i) All questions are compulsory.
(ii) Question nos. 1 to 8 are very short answer questions and carry 1 mark each.
(iii) Question nos. 9 to 18 are short answer questions and carry 2 marks each.
(iv) Question nos. 19 to 27 are also short answer questions and carry 3 marks each.
(v) Question nos. 28 to 30 are long answer questions and carry 5 marks each.
(vi) Use log tables if necessary, use of calculators is not allowed.
1. What is the total number of atoms per unit cell in a face centred cubic (fcc) structure?
Ans. The rank of fcc unit cell is 4.
2. What is primary cell? Given an example
Ans. The non-rechargeable cell is called primary cell.
Example: Dry cell.
3. What causes Brownian movement in a colloidal solution?
Ans. Collision between the particles of dispersed phase and dispersion medium.
4. In which one of the two structures, NO2+ and NO2-, the bond angle has a higher value?
Ans.
Number of electron pair around central atom =
sp hybridization state of central atom so bond angle is 180o.
Number of electron pair around central atom
sp2 hybridization state of central atom so bond angle is less than 120o due to the presence of lone pair of electron.
5. Write the IUPAC name of the following compound:
Ans. 2, 5-dimethyl hexan - 1, 3-diol.
6. Write the IUPAC name of the following compound
CH3COCH2COCH3.
Ans. CH3COCH2COCH3
IUPAC name of the above compound is Pentan-2, 4-dione.
7. Write a chemical reaction in which the iodide ion replaces the diazonium group in a diazonium salt.
Ans.
8. Name a substance that can be used as an antiseptic as well as a disinfectant.
Ans. Phenol is used as antiseptic in lower concentration while it is used as disinfectant in higher concentration.
9. State Raoult?s law for solutions of volatile liquid. Taking suitable examples explain the meaning of positive and negative deviations from Raoult?s law.
OR
Define the term osmotic pressure. Describe how the molecular mass of a substance can be determined by a method based on measurement of osmotic pressure.
Ans. In solution of volatile liquids, the partial vapour pressure of each component is directly proportional to its mole fraction.
where PA = partial vapour pressure of volatile liquid A
PB = partial vapour pressure of volatile liquid B
= vapour pressure of pure liquid A
vapour pressure of pure liquid B
xA and xB are mole fraction of liquid A and B in liquid phase.
Those non-ideal solutions, in which partial pressure of each component A and B is higher than that calculated from Raoult?s law shows positive deviation.
Example: water and ethanol.
If partial vapour pressure of component A and B is found to be less than calculated from Raoult?s law then such solution shows negative deviation from Raoult?s law.
Example: Chloroform and acetone.
OR
Osmotic pressure is defined as extra pressure that must be applied to the solution side to prevent the flow of solvent into solution through semi-permeable membrane.
Osmotic pressure is proportional to the molarity (M) of the solution at a given temperature T.
Thus p = MRT (1)
Here p is the osmotic pressure and R is the gas constant.
(2)
V is the volume of solution in litres containing n moles of the solute. If w g of the solute whose molecular mass is Msolute be present in the solution then
or (3)
Equation (3) on rearrangement gives
Thus, knowing quantities w, T, p and v molecular mass of the solute, Msolute can be calculated.
10. The conductivity of a 0.20 M solution of KCl at 298 K is 0.0248 S cm-1. Calculate its molar conductivity.
Ans. k = 0.0248 S cm-1 concentration of KCl solution is 0.1 M, molar conductivity of KCl solution Ùm = ?
Ùm = = S cm2 mol-1.
11. Formulate the galvanic cell in which the following reaction takes place L
State
(i) Which one of its electrodes is negatively charged.
(ii) The reaction taking place at each of its electrode.
(iii) The carriers of current within this cell.
Ans.
(i) Zn electrode is negatively charged electrode
(ii) At anode
At cathode
(iii) Current carriers of cell are
(a) electron in external wire
(b)Zn+2 in anodic half cell
(c) Ag+ in cathodic half cell
(d) ion of salt bridge i.e. K+ and Cl-
12. Define the following terms in relation to protein:
(i) Peptide linkage
(ii) Denaturation
Ans. (i) The reaction between two molecules of the same or different amino acids, proceed through the combination of the amino group of one molecule with the carboxyl group of the other, result in the elimination of a water molecule and formation of a peptide linkage -CO-NH-
(ii) The complex three-dimensional structure of proteins changes by change in pH, temperature and presence of salts or certain chemical compounds. This process of disruption of the native three-dimensional structure of proteins is called denaturation. During denaturation the protein will lose its biological activity.
13. List the reactions of glucose which cannot be explained by its open chain structure.
Ans. The following reactions of glucose cannot be explained by its open chain structure.
1. Despite having an aldehydic group, glucose does not given Schiff?s test.
2. It does not react with sodium bisulphite and ammonia
3. The pentaacetate of glucose does not react with hydroxylamine.
4. When glucose is treated with methanol in presence of dry hydrogen chloride gas, it yields two isomeric monomethyl derivatives known as methyl a-D-glucoside ad methyl b-D-glucoside.
5. The phenomenon of mutarotation.
14. Complete the following reaction equations
(i) C6H5N2Cl + KI ¾® ------
Ans. (i) C6H5N2Cl + KI ¾® C6H5I + KCl
15. (i) Why is it that haloalkanes are more reactive than haloarenes towards nucleophiles?
(ii) Which one of the following reacts faster in an SN1 reaction and why?
Ans. (i) Due to involvement of electron pair in resonance the C-X bond acquire double bond character which makes the removal of X- ion difficult in haloarene.
(ii)
Compound (I) reacts faster in SN1 since it is secondary alkyl halide while compound (II) is primary alkyl halide having least reactivity in SN1 reaction.
16. What are biodegradable and non-biodegradable detergents? Give one example of each class.
Ans. Branched hydrocarbon chain detergents are non biodegradable and cause water pollution.
For example
Unbranched or linear alkyl chain detergent are biodegradable.
For example
17. Assign a reason for each of the following statements:
(i) Ammonia is a stronger base than phosphine.
(ii) Sulphur in vapour state exhibits a paramagnetic behaviour.
Ans. (i) Due to small size of N atom of NH3 electron density is higher so as it can easily accept a proton in comparison of PH3.
(ii) In vapour state sulphur exist as discrete S2 molecule which are paramagnetic due to presence of odd electron.
18. Draw the structures of the following molecules:
(i) SF4
(ii) XeF4
Ans. (i) SF4
(ii) XeF4
19. What are lyophilic and lyophobic sols? Give one example of each type. Which one of these two types of sols is easily coagulated and why?
Ans. Lyophilic sols are defined as the colloidal solutions in which the particles of dispersed phase have great affinity for the dispersion medium. For example gums, gelatin etc. Lyophobic sols are those colloids which are solvent hating. In these colloids the particles of dispersed phase have no affinity for the dispersion medium for example colloidal solution of gold, silver etc.
Lyophobic sols are easily coagulated on the addition of small amounts of electrolytes because these are not stable.
20. Calculate the temperature at which a solution containing 54 of glucose, (C6H12O6), in 250 g of water will freeze.
(Kf for water = 1.86 K mol-1kg)
Ans. Given that
Mass of glucose w = 54g, molecular mass of glucose M = 180, Mass of water W = 250 g Kf for water = 1.86 K mol-1kg
DTf = Kf ´ molality
=
DTf = Tfo - Tf
\ Tf = - 2.23oC.
21. What is a semi-conductor? Describe the two main types of semiconductors and explain mechanisms for their conduction.
Ans. Those solids which have intermediate conductivities generally from 10-6 to 104 (ohm m)-1 are known as semiconductors.
Semiconductors are of two types
1. n-type semiconductor
2. p-type semiconductor
Conduction of semiconductors is due to movement of electrons from valence bond to conduction bond. In case of semiconductors the gap between valance bond and the conduction bond is small.
22. Write chemical equations for the following processes:
(i) Chlorine reacts with a hot concentrated solution of sodium hydroxide.
(ii) Orthophosphorous acid is heated.
(iii) PtF6 and xenon are mixed together.
OR
Complete the following chemical equations:
Ans. (i) 3Cl2 + 6NaOH ¾® 5NaCl + NaClO3 + 3H2O
(ii) 4H3PO3 3H3PO4 + PH3
(iii) PtF6 + Xe ¾® Xe[PtF6]
OR
(i) Ca3P2 + 6H2O ¾® 2PH3 + 3Ca(OH)2
(ii) Cu2+ + 4NH3(aq) ¾® [Cu(NH3)4] (OH)2
(excess)
(iii) F2 + H2O ¾® 2HF +
23. State briefly the principles which serve as basis for the following operations in metallurgy:
(i) Froth floatation process
(ii) Zone refining
(iii) Refining by liquation
Ans. (i) The principle of froth floatation process is that sulphide ores are preferentially wetted by the pine oil, whereas the gangue particles are wetted by the water.
(ii) Zone refining is based on the principle that impurities are more soluble in the melt than in the solid state of the metal.
(iii) Refining by liquation is based on the principle that impurities whose melting points are higher than metal are left behind on melting of impure metal. Hence pure metal separates out.
24. Account for the following observations:
(i) pKb for aniline is more than that for methylamine.
(ii) Methylamine solution in water reacts with ferric chloride solution to give
a precipitate of ferric hydroxide.
(iii) Aniline does not undergo Friedel-Craft?s reaction.
Ans. (i) Due to delocalization of electron pair of N in the aromatic ring through resonance aniline is weaker base than methyl amine so as its pKb will be smaller.
(ii) CH3NH2 + H - OH
FeCl3 + 3OH- ¾® Fe(OH)3 ¯ + 3Cl-
due to alkaline nature of solution of methyl amine precipitation of Fe(OH)3¯ occurs.
(iii) Due to lewis acid base reaction between nitrogen of aniline and AlCl3 the N acquires positive charge and deactivate the aromatic ring in consequence friedal craft?s reaction becomes difficult
25. Write the names and structures of the monomers of the following polymers:
(i) Buna-S
(ii) Neoprene
(iii) Nylon ? 6
Ans.
| Polymer | Monomer | Structure of monomer |
| (i) Styrene | 1, 3-butadiene and styrene |
|
| (ii) Neoprene | 2-chloro-1, 3-butadiene or chloprene |
|
| (iii) Nylon-6 | caparolactum |
|
26. Name the reagents which are used in the following conversions:
(i) A primary alcohol to an aldehyde.
(ii) Butan ? 2 ? one to butan ? 2-ol.
(ii) Phenol to 2, 4, 6-tribromophenol.
Ans. (i) Cu at 300oC or pyridinium chlorochromate.
(ii) LiAlH4/Ether
(iii) Br2/H2O
27. (a) What is a ligand ? Give an example of a bidentate ligand.
(b) Explain as to how the two complexes of nickel, [Ni(CN)4]2- and Ni(CO)4, have different structures but do not differ in their magnetic behaviour. (Ni=28)
Ans. (a) A molecule, ion or group that coordinates to a metal atom or ion in a complex compound is called ligand.
Ethylenediamine (H2NCH2CH2NH2) is bidentate ligand.
(b) Electronic configuration of Ni is [Ar] 3d84s2
Ni2+ [Ar] 3d8
CO and CN- both are strong field ligand hence these force paring of electrons
In [Ni(CN)4]2-
Hybridization state is dsp2 and structure is square planar. It is diamagnetic due to paired electrons.
In [Ni(CO)4]
Oxidation state of Ni is zero.
Hybridization state is sp3 and structure is tetrahedral. It is diamagnetic due to paired electrons.
28. (a) Derive the general form of expression for the half life of a first order reaction
(b) The decomposition of NH3 on platinum surface is a zero order reaction . What are the rate of production of N2 and H2 if k = 2.5 ´ 10-4 mol-1 L s-1?
OR
(a) List the factors that affect the rate of chemical reaction
(b) The half life of radioactive decay of 14C is 5730 years. An archaeological artefact containing would had only 80% of 14C activity found in living trees. Calculate age of artefact.
Ans. (a) A ¾® Product
a 0
a-x x
Rate at time t is given by
&nbs
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