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GOVERNMENT OF KARNATAKA

KARNATAKA STATE PRE‐UNIVERSITY EDUCATION EXAMINATION BOARD II YEAR PUC EXAMINATION

SCHEME OF VALUATION Subject Code : 34 Subject : Chemistry Qn.

No. PART – A Marks

1 ∆G° value for the formation of A2O and B2O are −827 kJ and −540 kJ which one of them is more stable? A2O 1

2 What is the colour of potassium dichromate in acidic medium? Orange red / orange 1

3 Name the method used for the isolation of noble gas mixture from air. Ramsay and Rayleigh method 1

4 How many ions are formed per molecule of potassium hexacyano ferrate (II) when dissolved in water? Five or 5 1

5 The reaction A + B → C follows first order kinetics with respect to A and second order kinetics with respect to B. What is the over all order of the reaction? Three or 3 1

6 Predict the sign of ∆S for the following process: H2O(g) → H2O (I)

Negative or −ve 1 7 Name the method used to determine the nature of charge on colloidal

particles. Electrophoresis 1

8 Which is the final product formed when methanamine is heated with excess of iodomethane in a sealed tube? tetramethylammonium iodide or (CH3)4 N+ I− or (CH3)4NI 1

9 Give an example for ketohexose. Fructose 1

10 How many polypeptide chains are joined together in insulin molecule? Two or 2 1

PART-B 11 State Nernst Distribution Law.

When a solute is dissolved in a mixture of two immiscible solvents, the solute distributes itself in such a way that, the ratio of concentration of solute in two solvents remains constant at constant temperature. 2

2

12 What happens when concentrated sulphuric acid is heated with oxalic

acid? Dehydration takes place OR CO & CO2 is liberated

OR self explanatory equation

1 1 2

13 Explain Linkage isomerism with an example. Compounds having the same molecular formula but differ in the mode of attachment of a ligand to the central metal atom/ion.

Or A type of structural isomerism in which isomers differ in the ligating atom of ambident ligand.

Or A type of structural isomerism that occurs when more than one type of atom in a monodentate ligand acts as a donor atom . [Co NO2 (NH3)5] Cl2 & [Co ONO (NH3)5]Cl2 or its complex ions Or [Cr SCN (H2O)5]2+ & [Cr NCS (H2O)5]2+ OR names

1 1

14 Define the term ‘Temperature coefficient’. Write its mathematical expression. The ratio of rate constants of a reaction at two temperatures differing by ten degrees. OR The ratio of rate constants of a reaction at ( t+10)°C and at t°C

OR The ratio of rate constants of a reaction at a given temperature and at ten degrees (10°) lower temperature

Temperature coefficient = ( )T 10

T

k

k+

1 1

15 Give two conditions for the positive deviation of non-ideal solutions. 1. A-----B interactions are smaller than A-----A and B----B interactions 2. PA > 0

AP XA ; PB > 0BP XB

3. ∆H mixing > 0 OR positive or +ve 4. ∆V mixing > 0 OR positive or +ve ( Any two points ) 2

3

16 Write two differences between lyophilic sols and lyophobic sols.

Lyophilic sol Lyophobic sol i. They are reversible ii. Quite stable iii. Prepared by simple method iv. Particles are solvated. v. Dispersed phase has strong

affinity for dispersion medium. vi. Particles may or may not be

charged vii. Surface tension is lower than

dispersion medium. viii. Viscosity is higher than

dispersion medium

i. Irreversible ii. Less stable iii. Prepared by indirect method iv. Not solvated v. Dispersed phase has less

affinity for dispersion medium. vi. Particles are charged vii. Surface tension is almost the

same as dispersion medium. viii. Viscosity is almost the

same as dispersion medium Any two differences among these 2

17 What is radius ratio? Give the shape of the molecule having limiting radius ratio 0.414 to 0.732. Ratio of radius of cation to the radius of anion is called radius ratio.

OR radius ratio = rr

+

−

Octahedral 1 1

18 Define the term enantiomerism. Write the structural formula of lactic acid enantiomers. The optical isomers of a compound which are non-super imposable mirror images of each other are called enantiomers.

(or any other form)

1 1

19 Give two postulates of Baeyer’s strain theory of cycloalkanes. 1. All cycloalkanes are planar. 2. The deviation from normal tetrahedral bond angle causes some strain

on the molecule. It is called angle strain. 3. Greater the angle strain, less stable is the cycloalkane. 4. Cycloalkanes which are stable can be prepared easily. (any two points ) 2

20 How do you convert ethane nitrite to ethanamine ? Give equation. Instead of ethanenitrile it is printed as ethane nitrite. If the Q.No. is written / attempted. 2

4

21 Give a reaction to show glucose molecule contains

i) Five hydroxyl (−OH) groups It reacts with acetyl chloride or acetic anhydride, to form a pentaacetyl

derivative ii) A terminal aldehydic group. With bromine water it gives a carboxylic acid having same number of

carbon atoms as in glucose OR when glucose is heated with nitric acid it forms dicarboxylic acid

having same number of carbon atoms as in glucose

1 1

22 What is rancidity of oils and fats? How it can be prevented? Bad / unpleasant smell developed when oil or fat is exposed to warm moist air. Addition of vitamin C and E OR refrigeration OR adding antioxidants OR store in cool dry place. (Any one)

1 1

PART-C 23 a) Write chemical reactions taking place in the blast furnace at

reduction zone, slag formation zone and combustion zone during the extraction of Iron.

At reduction zone: Ferric oxide is reduced to iron by carbon monoxide OR Fe2O3 + 3 CO 600 700 C− °→ 2Fe + 3CO2 Slag formation zone: Limestone decomposes to form calcium oxide, which then combines with silica to form calcium silicate slag OR CaCO3 900 C°→CaO + CO2 CaO + SiO2 → CaSiO3 Combustion Zone : Coke burns in oxygen to form carbon dioxide. OR C + O2 1500 C°→ CO2 (Temperatures are not value points)

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b) Mention the geometry and magnetic property of tetracarbonylnickel (o) complex

Tetrahedral or if written the structure Diamagnetic

1 1

5

24 a) Describe the Haber’s process for the manufacture of Ammonia.

N2 + 3H2 2NH3

Pure nitrogen and hydrogen in the ratio 1: 3 by volume at a pressure of 200 atm is introduced in to the catalytic converter. It contains Fe and Mo maintained at 450° C. Nitrogen combines with hydrogen and forms ammonia. Gases are condensed. Ammonia liquifies. The unreacted gases are recycled. (If conditions are not mentioned, deduct one mark)

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b) How is xenonhexafluoroplatinate (V) prepared by Bartlett method? Xenon is treated with platinum hexafluoride to get the compound. Xe + PtF6 →Xe[PtF6]

OR Self explanatory equation

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25 a) Explain colour of transition metal compounds based on crystal field splitting.

Colour of transition metal compounds is possible when they have partially filled ‘d’ sub-shell or have unpaired electrons.

When visible light (white light) falls on these, a part of the radiation is absorbed to excite or promote an electron from one set of d orbitals to the other. OR diagram

Unabsorbed radiations are transmitted. This gives colour to the compound

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b) Account for the malleability and ductility of metals on the basis of electron gas theory.

When force (stress) is applied to a metal kernels (positive ions or lattice points) layers slide over one another. The shape of the metal gets deformed.

Freely moving electrons also move around the deformed layers and the environment around the metal ions remains unchanged.

OR

According to electron gas theory, a metal contains an array of positively charged metal ions in a sea of mobile valence electrons and the bonding is non-directional.

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6

When force is applied to a metal, the kernel layers slide over one another. The shape of the metal gets deformed. OR

1

26 a) Explain the mechanism of nitration of benzene. HNO3 + H2SO4 → H2O + 2NO+ + 4HSO− OR HNO3 + 2H2SO4 → H3O+ + 2NO+ + 2 4HSO−

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b) Give two differences between inductive effect & mesomeric effect. Inductive effect Mesomeric effect

1. Observed in saturated compounds.

2. Partial displacement of σ electrons.

3. Effect decreases with distance.

1. Observed in conjugated system.

2. Delocalisation of π electrons. 3. Effect remains same

throughout the system. Any two differences.

2

27 a) How is phenol isolated from coal tar? Middle oil (170-230°C) contains mainly phenols naphthalene and traces of pyridine. It is cooled. Naphthalene crystallises. It is removed by filtration.

Crude phenol is washed with dilute H2SO4, then treated with sodium hydroxide solution. Sodium phenate formed in aqueous solution is separated, acidified to get phenol. C6H5OH + NaOH →C6H5ONa + H2O C6H5ONa + HCl →C6H5OH + NaCl (For acidification CO2 or H2SO4 can be used)

1 1

½ ½

b) Explain Wurtz-Fitting reaction with an example. When alkyl halide is heated with aryl halide with sodium in dry ether alkyl benzene (arene) is obtained. Any example with equation.

OR When chlorobenzene is heated with chloromethane in presence of sodium in dry ether, methylbenzene (toluene) is formed.

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7

C6H5Cl + 2Na + CH3Cl dry ether∆→C6H5−CH3 + 2NaCl

OR C6H5Cl + 2Na + CH3Cl dry ether

∆→ C6H5−CH3 + 2NaCl

chlorobenzene methyl chloride toluene OR

(any other example)

1 2

28 a) Explain 2NS mechanism with an example.

Methyl bromide undergoes hydrolysis with aqueous NaOH to form methyl alcohol

OR CH3Br + NaOH (aq) →CH3OH + NaBr The nucleophile −OH - attacks from rear side of the bromine atom to give a transition state in which C−OH bond is partially formed & C−Br bond is partially broken. This loses Br− ion to give methyl alcohol.

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b) How do you convert ethanoic acid to methane? Write equation. Ethanoic acid heated with soda lime, sodium ethanoate formed undergoes decarboxylation to form methane.

OR By heating it with soda lime.

CH3COOH NaOH→CH3COONa soda lime∆→CH4

OR CH3COOH + NaOH , CaO∆→CH3COONa + H2O CH3COONa + NaOH , CaO∆→CH4 + Na2CO3

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29 a) With an example explain the following : i) Clemmensen’s reduction

When a ketone is treated with Zn−Hg/ conc. HCl a hydrocarbon is obtained. Any example with equation.

OR When acetone/ acetophenone is treated with zinc amalgam and concentrated HCl, propane / ethylbenzene is obtained. CH3COCH3 + 4[H] Zn-Hg

Conc. HCl→ CH3−CH2−CH3 + H2O

OR C6H5COCH3 + 4[H] Zn-Hg

Conc. HCl→ C6H5−CH2−CH3 + H2O

OR self explanatory equation

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ii) Kolbe’s reaction. Dry sodium phenate is heated with carbon dioxide at 140°C under 4-7 atm pressure. The product obtained on acidification gives salicylic acid

OR

Self explanatory equation

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b) Name the product formed when ethanoic acid is heated with ethanol in the presence of concentrated sulphuric acid.

ethylethanoate or ethyl acetate

1

30 a) Thermal decomposition of a compound is of first order. If 50% of the compound is decomposed in 120 minute, how much time it take for the 90% decomposition of the compound?

k = 2.303 alogt a x−

k = 12

0.693t

k = 0.693120

= 5.775 × 10−3 min−1

t = 3

2.303 100log5.775 10 10−×

t = 398.78 min OR t = 23,926 s (OR by any other method)

1

½

½ 1

b) Explain with an example, “conjugate acid base pair”. Acid-base pair that differ by a proton. HCl / Cl− or H2O / −OH or NH3 / 4NH+ or any other example

1 1

31 a) Explain the mechanism of buffer action of acetic acid and sodium acetate buffer.

CH3COOH CH3COO− + H+ CH3COONa →CH3COO− + Na+ Case-i) When an acid is added, H+ ions react with acetate ions to form acetic acid. Hence pH almost remains same. H+ + CH3COO− CH3COOH Case-ii) When a base is added, the −OH ions react with acetic acid to form acetate ions and water. Hence pH almost remains same. CH3COOH + −OH CH3COO− + H2O (Reversible arrows in case i and ii have no value points)

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b) Write Gibb’s-Helmholtz equation. For a process, if ∆H and T∆S are positive and T∆S > ∆H, predict the spontaneity of the process.

∆G = ∆H − T∆S OR ∆G° = ∆H° − T∆S° The process is spontaneous.

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32 a) Describe the construction and working of the Daniel cell. Write cell representation.

At anode zinc gets oxidised. Electrons flow through external circuit. At cathode Cu+2 ions get reduced.

OR At anode: Zn → Zn+2 + 2e− At cathode: Cu+2 + 2e− → Cu

Zn(s) | Zn+2(aq) || Cu+2 (aq) | Cu(s)

(s and aq are not value points)

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b) Explain Ostwald’s isolation method for the determination of order of a reaction.

Consider a reaction A + B → products.

Case-i) A is taken in small amounts and B in large excess. Order with respect to A is determined. Let it be x.

Case-ii) B is taken in small amounts and A in large excess. Order with respect to B is determined. Let it be y. Order of the reaction is x + y.

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33 a) Explain the application of common ion effect and solubility product in the precipitation of second group basic radicals.

Ksp value of sulphides II group is very low. In presence of dilute HCl, the degree of dissociation of H2S is suppressed, due to the common ion H+. Low concentration of S−2 is enough to make ionic product of sulphides of II group to exceed their Ksp value

OR Low concentration of s−2 is sufficient to precipitate II group basic radicals.

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10

b) Define “lowering of vapour pressure”. Give equation for Raoult’s

law of relative lowering of vapour pressure. Difference between vapour pressure of a pure solvent and that of the solution.

OR

When a non-volatile solute is dissolved in a volatile solvent, vapour pressure of the solution decreases.

2

1 2

P P nP n n° −

=° +

OR P PP° −

=°

XB OR 0A S 2

0A 1 2

P P nP n n−

=+

1 1

34 a) Rusting of iron is an electrochemical phenomenon. Explain. Iron metal acts as anode. Impurities in iron piece act as cathode. Moisture on it containing dissolved CO2 and O2 acts as electrolyte. A series of galvanic cells are set up. Anodic reaction: Fe → Fe+2 + 2e−

Cathodic reaction: H2O + 12

O2 + 2e− → 2OH−

Ferrous ions gets oxidised to ferric ions and finally forms hydrated ferric oxide (rust)

1 1 1

b) What is Brownian movement? How is it caused?

Zig-zag or random movement of colloidal particles in a medium. Due to unequal bombardment of the particles of the medium with colloidal particles.

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PART-D D1

35. a)Write the postulates of Werner’s theory of coordination compounds. i) Metal that forms a coordination compound exhibits two types of

valencies: primary and secondary. ii) Primary valency is ionisable, secondary is not. iii) Primary valency indicates the oxidation state. iv) Secondary valency indicates the coordination number. v) Primary valency is satisfied by anions, secondary valency by ligands. vi) Secondary valency has directional properties. (Any three – 1 mark each)

3

11

b) Calculate the mass of hydrogen gas evolved by passing a current of 0.5 ampere for 40 minutes through acidified water.

m = Zit OR m = Z I t OR m = Eit96,500

m = 1 0.5 40 6096,500

× × × = 0.0124 g

1 1

c) i) Define Unit Cell. It is the smallest repeating unit of a crystal which when placed in 3 dimensions gives the crystal lattice. ii) Give reason : equimolar solutions of sodium chloride and glucose

do not have the same osmatic pressure. The number of solute particles are not the same.

OR Sodium chloride ionises but glucose does not.

OR Number of solute particles in NaCl solution is greater than that in glucose.

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d) What is Zwitter ion ? Write Zwitter ion structure of Alanine. Dipolar ion or internal salt

OR it is the dipolar ion formed due to transfer of proton (H+) from −COOH group to −NH2 group in an amino acid

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e) Give an example for drying oil. Linseed oil or chain wood oil or tung oil

1

36 a) Write energy level diagram, bond order and magnetic property of lithium molecule on the basis of Molecular Orbital Theory.

Bond order = 1 or one Diamagnetic

1 1 1

12

b) Write four assumptions of Arrhenius theory of electrolytic dissociation.

i) When an electrolyte is dissolved in water its molecules split up into electrically charged particles called ions.

ii) Total charge on cations is equal to charge on anions. iii) Ionisation is a reversible process. iv) Ions are responsible for passage of electric current through the solution. v) Degree of dissociation increases with dilution. vi) Property of electrolyte in solution is properties of ions present in it. (Any four)

4

c) Outline the mechanism of Cannizzar’s reaction in benzaldehyde.

C6H5COOH + C6H5CH2O− + Na+ →C6H5COONa + C6H5CH2OH (Instead of Na+, K+ can also be used) (Reversible arrow has no value point)

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PART-D D2

37 a) Explain the laboratory method of preparation of p-bromoacetanilide from acetanilide

2g of acetanilide + 5 ml of glacial acetic acid + 5 ml of bromine in acetic acid is mixed in a conical flask. The mixture is kept aside for 5 minutes and contents are poured into cold water. A white precipitate of p-bromo acetanilide is obtained. (Quantity of the reactants not a value point)

1 1 1

b) Mention a general test for the following : i) Carbohydrates : Molisch’s test OR test ii) Oils and fats : Acrolein test OR test

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13

38 Describe an experiment to show that the effect of temperature on the rate of reaction between potassium persulphate and potassium iodide. K2S2O8 + 2KI → 2K2SO4 + I2 Procedure: Prepare the reaction mixture by mixing 25 ml each of 0.1 N K2S2O8 + 0.1 N KI kept at t1°C and start the stop clock. At regular intervals of time, a sample of the mixture (5 ml) is pipetted into a conical flask containing ice cold water (and little KI). It is then titrated against 0.1N Na2S2O3 using starch as indicator (added near the end point). End point is disappearance of blue colour. Volume of Na2S2O3 consumed is recorded. Repeat the above procedure by keeping the reactants at t2°C (t2 > t1).

Conclusion: The rate of chemical reaction increases with increase in temperature.

Burette reading Time

Final Initial

Vol. of Na2S2O3

5

10

15

20

25

1 2

12

+ 12

1

39. For the estimation of ammonium ferrous sulphate (Mohr’s salt) using standard potassium dichromate solution. i) Write the balanced chemical equation of the reaction. K2Cr2O7 + 4H2SO4 →K2SO4 + Cr2(SO4)3 + 4H2O + 3(O) [2FeSO4 + H2SO4 + (O) → Fe2(SO4)3 + H2O] × 3

OR K2Cr2O7+6FeSO4+7H2SO4 →K2SO4 + Cr2(SO4)3 + 3Fe2(SO4)3 +7H2O ii) Give the equivalent mass of Mohr’s salt. 392 iii) Name the indicator used. Diphenylamine iv) Mention the colour change at the end point. Green to violet

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