CBSE Sample Papers for Class 12 Chemistry Solved 2016 Set 3
Section A
1.Which of the following has higher boiling point?
(i)Chlorobutane
(ii)2-methyl-2-chlorobutane
2.What are the importance of Brownian movement?
3.Write Reimer-Tiemann reaction and also give an example
4.Complete the following reaction.
5.Convert toluene to 2-phenylethanamine.
Section B
6.Write the formula and the structure of noble of a reaction gas species (one each) which are isostructural with (i)ICL4– (ii) BrO–3
7.Distinguish between molecularity and order
8.Formulate the galvanic cell in which the following reaction takes place.
Zn(s) + 2Ag+ (ag)———- > Zn2+ (ag) + 2Ag(s)
(i)Which one of its electrodes is negatively charged?
(ii)Write the reaction taking place at each of its electrode.
(iii)What are the carriers of current within the cell?
9.The composition of a sample of wurtzite is Fe0.93 O1.00.What percentage of the iron is present in the form of Fe(III)?
Or
Assign reasons for the following.
(i)Phosphorus doped silicon is a semiconductor.
(ii)Some of the very old glass objects appear slightly milky instead of being transparent.
Section C
11.(i) Predict the structure of SO3 and the angle O—S— O.
(ii)Explain thef ollowing observations.
(a)Oxygen is a gas but sulphur is a solid.
(b)The halogens are coloured, why?
12.(i) Why is CO a stronger ligand than CP?
(ii) What is meant by crystal field splitting energy? How does the magnitude of splitting decide the actual configuration of d-orbitals in an octahedral field for a coordination entity?
13.(i) Write the structure of 2-(2-bromophenyl) butane.
(ii) Haloalkanes react with KCN to form alkyl cyanides as the main product while with AgCN, forms isocyanides, as the main product. Explain.
14.(i) Illustrate the Gattermann reaction with an example.
(ii) Give chemical tests to distinguish between a primary and a secondary amine.
15.The electrical resistance of a column of 0.05 M NaOH solution of diameter 1 cm and length 50 cm is 5.55 x 103 ohms Calculate its resistivity, conductivity and molar conductivity.
16.Distinguish between multimolecular, macromolecular and associated colloids Give one example of each.
17.(i) Both aluminium and iron combine slowly with oxygen at room temperature. Why is this reaction a problem for iron but not for aluminium?
(ii)Explain Mond’s process.
(iii)Convert impure copper to pure copper.
18.(i) In the decomposition of N205, the plot between the reciprocal of concentration of the reactant and the time was found to be linear. Determine the order of the reaction.
(ii) The rate of a reaction quadruples when the temperature changes from 293K to 313K. Calculate the energy of activation of the reaction assuming that it does not change with temperature.
19.(i) Arrange the following order of property indicated with reason.
(a)Cl02– , C120, C102 in the increasing order of bond angle.
(b)C1F3, BrF3, IF3 in the decreasing order of stability.
(ii) Phosphorus has a greater tendency for catenation than nitrogen. Why?
20.Name the reagents which are used in the following conversions.
(i)A primary alcohol to an aldehyde
(ii)Butane-2-one to butane-2-ol
(iii)Phenol to 2,4,6-tribromophenol
21.Enumerate the reactions of D-glucose that cannot be explained by the open chain structures.
Or
What happens when D-glucose is treated with the following reagents?
(i) HI (ii) Br2 water
(iii)HN03
22.(i) Write the name of monomer of PMMA and state its one use.
(ii)What does designation, 66 in nylon-66 polymer mean?
(iii)Which polymer is obtained when free radical polymerisation of chloroprene occurs? Write the structure of the polymer thus obtained.
Section D
23.My father is diabetic but is fond of cold drinks, which have sugar content in it. Doctor advised me to give him low calorie drinks and I follow doctor so the diabeties of my father is under controlled.
(i)What is the advantage of taking low calorie drinks?
(ii)Give names of two preservatives used in soft drinks.
(iii)Write the value associated with the author of paragraph
Section E
24.(i) Explain the mechanism of nucleophilic attack on the carbonyl group of an aldehyde or a ketone.
(ii) An organic compound A (molecular formula = C8H1602) was hydrolysed with dilute sulphuric acid to give a carboxylic acid B and an alcohol C. Oxidation of C with chromic acid also produced B. On dehydration, C gives but-l-ene. Identify A, B and C.
Or
An organic compound A on treatment with acetic acid in the presence of sulphuric acid produces an ester B.A on mild oxidation gives C. C with 50% KOH followed by acidification with dil.HCl generates A and D. D with PC15 followed by reaction with NH3 gives E. E on dehydration produces HCN.Identify A to E.
26.(i) Calculate the vapour pressure of solution having 3.42 g of cane sugar in 180g of water at 40°C and 100°C. Given that the boiling point of water is 100°C and heat of vaporisation is 10 K cal mol-1 in the given temperature range. Also, calculate the lowering in vapour pressure of 0.2m cane sugar at 40°C.
(ii) The molecular masses of polymers are determined by osmotic pressure method and not by measuring other colligative properties. Give two reasons.
Or
Calculate the depression in freezing point of water when 20.0 g of CH3CH2CHClCOOH is added to 500 g of water.[Given Ka = 1.4×10-3,Kf =1.86 K kg mol-1]
Answers
Section A
1.Which of the following has higher boiling point?
(i)Chlorobutane
(ii)2-methyl-2-chlorobutane
Ans.
Chlorobutane has higher boiling point than 2-methyl-2-chlorobutane because boiling point depends on surface area and van der Waals’ forces and decreases on branching and 2-methyl-2-chlorobutane is in branched form, that’s why its boiling point is less than that of chlorobutane.
2.What are the importance of Brownian movement?
Ans.(i) It helps in the determination of Avogadro’s number.
(ii) It opposes the forces of gravity and does not allow the colloidal particle to settle down
3.Write Reimer-Tiemann reaction and also give an example
Ans.The reaction of phenol with chloroform in the presence of an alkali to give o and p-hydroxyaldehyde is known as Reimer-Tiemann reaction. For example,
4.Complete the following reaction.
5.Convert toluene to 2-phenylethanamine.
Ans.
Section B
6.Write the formula and the structure of noble of a reaction gas species (one each) which are isostructural with (i)ICL4– (ii) BrO–3
Ans.
7.Distinguish between molecularity and order
Ans.
8.Formulate the galvanic cell in which the following reaction takes place.
Zn(s) + 2Ag+ (ag)———- > Zn2+ (ag) + 2Ag(s)
(i)Which one of its electrodes is negatively charged?
(ii)Write the reaction taking place at each of its electrode.
(iii)What are the carriers of current within the cell?
9.The composition of a sample of wurtzite is Fe0.93 O1.00.What percentage of the iron is present in the form of Fe(III)?
Or
Assign reasons for the following.
(i)Phosphorus doped silicon is a semiconductor.
(ii)Some of the very old glass objects appear slightly milky instead of being transparent
Or
(i)When silicon is doped with a group 15 element like phosphorus,(pentavalent), the conductivity of doped silicon crystal increases due to the extra free delocalised electrons. Therefore, phosphorus doped silicon, is a semiconductor.
(ii)Glass is a supercooled liquid or pseudo solid. At higher temperatures, glass slightly melts and recrystallises. Due to the repetition of this process, the arrangement of glass molecules becomes disordered and the glass objects appear slightly milky instead of being transparent.
Section C
11.(i) Predict the structure of SO3 and the angle O—S— O.
(ii)Explain thef ollowing observations.
(a)Oxygen is a gas but sulphur is a solid.
(b)The halogens are coloured, why?
Ans.
(ii) (a) Oxygen, due to its small size, high electronegativity and absence of d-orbitals, forms pn-pn multiple bonds and exists as discrete diatomic (02) molecule. But sulphur contains d-orbitals, so it can expand its covalency, moreover, the S—S single bond is stronger than the 0—0 single bond. So, it has a tendency to show catenation and exists as polyatomic S8 molecule, which is a solid.
(b) All halogens are coloured due to the absorption of radiations in visible region which results in the excitation of outer electrons to higher energy level. While the remaining light is transmitted. The colour of halogens is actually the colour of this transmitted light, i.e. halogens have complementary colour.
12.(i) Why is CO a stronger ligand than CP?
(ii) What is meant by crystal field splitting energy? How does the magnitude of splitting decide the actual configuration of d-orbitals in an octahedral field for a coordination entity?
Ans.
13.(i) Write the structure of 2-(2-bromophenyl) butane.
(ii) Haloalkanes react with KCN to form alkyl cyanides as the main product while with AgCN, forms isocyanides, as the main product. Explain.
Ans.
14.(i) Illustrate the Gattermann reaction with an example.
(ii) Give chemical tests to distinguish between a primary and a secondary amine.
Ans.(i) Gattermann reaction In this reaction, chlorine or bromine group is introduced in the benzene ring by treating the diazonium salt solution with corresponding halogen acid in the presence of copper powder. For example,
(ii) The chemical tests to distinguish between a primary and a secondary amine is given below.
15.The electrical resistance of a column of 0.05 M NaOH solution of diameter 1 cm and length 50 cm is 5.55 x 103 ohms Calculate its resistivity, conductivity and molar conductivity.
16.Distinguish between multimolecular, macromolecular and associated colloids Give one example of each.
Ans.(i) Multimolecular colloids These consist of aggregates of atoms or molecules having diameter less than 1 nm.For example, sulphur sol consists of particles containing a thousand or more (S8) sulphur molecules
(ii)Macromolecular colloids These consist of large sized molecules and the size of the macromolecule is in colloidal range. Starch, cellulose, proteins and enzymes are naturally occurring macromolecules. Polythene, nylon, polystyrene and synthetic rubber are man-made macromolecules.
(iii)Associated colloids Soaps and detergents in higher concentrations form associated colloids. Molecules of soaps and detergents consist of lyophilic as well as lyophobic parts which associate together to form micelles (associated colloids). At low concentration, they behave as normal electrolyte. Micelles may contain as many as 100 molecules or more.
17.(i) Both aluminium and iron combine slowly with oxygen at room temperature. Why is this reaction a problem for iron but not for aluminium?
(ii)Explain Mond’s process.
(iii)Convert impure copper to pure copper.
Ans.
18.(i) In the decomposition of N205, the plot between the reciprocal of concentration of the reactant and the time was found to be linear. Determine the order of the reaction.
(ii) The rate of a reaction quadruples when the temperature changes from 293K to 313K. Calculate the energy of activation of the reaction assuming that it does not change with temperature.
19.(i) Arrange the following order of property indicated with reason.
(a)Cl02– , C120, C102 in the increasing order of bond angle.
(b)C1F3, BrF3, IF3 in the decreasing order of stability.
(ii) Phosphorus has a greater tendency for catenation than nitrogen. Why?
20.Name the reagents which are used in the following conversions.
(i)A primary alcohol to an aldehyde
(ii)Butane-2-one to butane-2-ol
(iii)Phenol to 2,4,6-tribromophenol
Ans.
21.Enumerate the reactions of D-glucose that cannot be explained by the open chain structures.
Or
What happens when D-glucose is treated with the following reagents?
(i) HI (ii) Br2 water
(iii)HN03
Ans.Open chain structures of D-glucose could not explain the following reactions.
(i)Despite having the aldehyde group, glucose does not give Schiff’s test and 2,4-DNP test.
(ii)Glucose does not react with sodium hydrogen sulphite to form a4n additional product.
(iii) The pentaacetate of glucose does not react with hydroxyl amine showing the absence of free — CHO group.
Or
22.(i) Write the name of monomer of PMMA and state its one use.
(ii)What does designation, 66 in nylon-66 polymer mean?
(iii)Which polymer is obtained when free radical polymerisation of chloroprene occurs? Write the structure of the polymer thus obtained.
Section D
23.My father is diabetic but is fond of cold drinks, which have sugar content in it. Doctor advised me to give him low calorie drinks and I follow doctor so the diabeties of my father is under controlled.
(i)What is the advantage of taking low calorie drinks?
(ii)Give names of two preservatives used in soft drinks.
(iii)Write the value associated with the author of paragraph
Ans.(i) In low calorie drinks, artificial sweetening agents are present. They do not metabolise.
(ii)Preservatives used in soft drinks are sodium benzoate or citric acid and sodium bicarbonate.
(iii)Caring attitude towards his father and awareness about his health.
Section E
24.(i) Explain the mechanism of nucleophilic attack on the carbonyl group of an aldehyde or a ketone.
(ii) An organic compound A (molecular formula = C8H1602) was hydrolysed with dilute sulphuric acid to give a carboxylic acid B and an alcohol C. Oxidation of C with chromic acid also produced B. On dehydration, C gives but-l-ene. Identify A, B and C.
Or
An organic compound A on treatment with acetic acid in the presence of sulphuric acid produces an ester B.A on mild oxidation gives C. C with 50% KOH followed by acidification with dil.HCl generates A and D. D with PC15 followed by reaction with NH3 gives E. E on dehydration produces HCN.Identify A to E.
Ans.
26.(i) Calculate the vapour pressure of solution having 3.42 g of cane sugar in 180g of water at 40°C and 100°C. Given that the boiling point of water is 100°C and heat of vaporisation is 10 K cal mol-1 in the given temperature range. Also, calculate the lowering in vapour pressure of 0.2m cane sugar at 40°C.
(ii) The molecular masses of polymers are determined by osmotic pressure method and not by measuring other colligative properties. Give two reasons.
Or
Calculate the depression in freezing point of water when 20.0 g of CH3CH2CHClCOOH is added to 500 g of water.[Given Ka = 1.4×10-3,Kf =1.86 K kg mol-1]
Ans.
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