CBSE Sample Papers for Class 12 Chemistry Solved 2016 Set 8

CBSE Sample Papers for Class 12 Chemistry Solved 2016 Set 8

                                              Section A

1.Give one point of difference between adsorption and absorption.

2.How is ethanol obtained from 2-butene?

3.Write the IUPAC name of the following compound.

4.The deficiency of which vitamins causes the disease
(i)Pernicious anaemia?
(ii)Night blindness?

5.What type of defect is produced when NaCl is doped with SrCl₂ ?

                                             Section B

8.(i)Mn(II) shows maximum paramagnetic character amongst the divalent ions of the first transition series.
(ii) Most of the transition metals do not displace hydrogen from dilute acids, why?

9.Explain, why does colour of KMn0₄ disappear when oxalic acid is added to its solution in acidic medium?

10.Complete the following reactions.
(i)C₆H₅NH₂ + Br₂ (ag)—- >
(ii)C₆H₅NH₂ + (CH₃C0)₂0 —— >
Or
Draw the structures of the different isomers aliphatic amines corresponding to the molecular formula C₃H₉N.

                                                          Section C

11.(i) Draw the structure (structural formula) of pyrophosphate ion.
(ii) PH₃ forms bubbles when passed slowly in water but NH₃ dissolves. Explain, why?

12.(i) Iron has a body centred cubic cell with a cell edge of 286.5 pm. The density of iron is 7.87 g cm^-3 . Use this information to calculate the Avogadro’s number.[Atomic mass of Fe =56 gmoT¹]
(ii) How does the structure of quartz and quartz glass differ from each other?

17.Explain the terms.
(i)Electrophoresis (ii) Coagulation                     (iii) Hardy Schulze law

18.Write down the IUPAC name for each of the following complexes and indicate the oxidation state, electronic configuration and coordination number. Also give stereochemistry and magnetic moment of the complex.
(i) [CrCl₃(Py)₃]           (ii) K₄[Mn(CN)₆]                    (iii) Cs[FeCl₄]

19.(i) Explain, why propanol has higher boiling point than that of the hydrocarbon butane?
(ii)Write the mechanism of hydration of ethene to yield ethanol.

21.(i) How does the presence of double bonds in rubber molecules influence their structures and reactivity?
(ii) Discuss the main purpose of vulcanisation of rubber.

22.(i) Name a substance which can be used as an antiseptic as well as disinfectant.
(ii)Name a sweetning agent used in the preparation of sweets for a diabetic patient.
(iii)What are the main constituents of dettol?
Or
(i)Which type of drugs come under antimicrobial drugs?
(ii)What is the harmful effect of hyper acidity?
(iii)Which site of an enzyme is called allosteric site?

                                                Section D

23.Saxena, head of metallurgical division Based on the above passage, answer the always insisted for refining of copper by  electrolytic method, instead of other  convenient methods, inspite of the fact   that it is power consuming and takes  longer time. Based on the above passage, answer the following questions.
(i)Is electrolytic refining environmental friendly or economical?
(ii) How cathode, anode and electrolyte used in this process?
(iii)Write the values shown by Mr. Saxena.

                                                        Section E

24.A mixture of two aromatic compounds A and B was separated by dissolving it in chloroform followed by the extraction with aqueous KOH solution. The organic layer containing compound A, when heated with alcoholic solution of KOH produced a compound C (C₇H₅N) associated with an unpleasant odour. The alkaline aqueous layer on the other hand, when heated with chloroform and then acidified gave a mixture of two isomeric compounds D and E of molecular formula C₇H₆0₂. Identify the compounds A, B, C, D and E and draw their structures.
Or
Predict the product when cyclohexane carbaldehyde reacts with following reagents.
(i)C₆H₅MgBr followed by H₃0⁺
(ii)Tollen’s reagent
(iii)Semicarbazide in the weakly acidic medium
(iv)Excess of ethanol in the presence of acid
(v)Zinc amalgam and dilute hydrochloric acid

25.(i) Considering the parameters such as bond dissociation enthalpy, electron gain enthalpy and hydration enthalpy, compare the oxidising power of F₂ and Cl₂.
(ii) Give two examples to show the anomalous behaviour of fluorine.
Or
On heating, compound A gives a gas B which is a constituent of air. This gas when treated with 3 moles of hydrogen H₂ in the presence of a catalyst gives another gas C which is basic in nature. Gas C on further oxidation in moist condition gives a compound D which is a part of acid rain. Identify compounds A to D and also give necessary equations of all the steps involved

26.A first order reaction, A—— » B, requires activation energy of 70 kJ mol^-1. When a 20% solution of A was kept at 25°C for 20 minutes, 25% decomposition took place. What will be the per cent decomposition at the same time in a 30% solution maintained at 40°C? Assume that activation energy remains constant in this range of temperature.
Or
(i)Mention the factors that affect the rate of a chemical reaction.
(ii)A reaction is of second order with respect to a reactant. How is the rate of reaction affected if the concentration of the reactant is
(a)doubled?
(b)reduced to half?
(iii)What is the effect of temperature on the rate constant of a reaction? How can this temperature effect on rate constant be represented quantitatively?

Answers

                                                      Section A

1.Give one point of difference between adsorption and absorption.
Ans.Adsorption is the surface phenomenon but absorption takes place in the bulk of the solid.

2.How is ethanol obtained from 2-butene?
Ans.

3.Write the IUPAC name of the following compound.

Ans.

4.The deficiency of which vitamins causes the disease
(i)Pernicious anaemia?
(ii)Night blindness?
Ans.(i) Pernicious anaemia-Vitamin B12 (ii) Night blindness- Vitamin A

5.What type of defect is produced when NaCl is doped with SrCl₂ ?
Ans.Vacancy (metal deficiency type) defect is produced when NaCI is doped with SrCI2.

                                             Section B

Ans.(i) The properties of solutions which depend upon the number of solute particles irrespective of their nature relative to the total number of particles present in the solution, are known as colligative properties, e.g. osmotic pressure.

Ans.

8.(i)Mn(II) shows maximum paramagnetic character amongst the divalent ions of the first transition series.
(ii) Most of the transition metals do not displace hydrogen from dilute acids, why?
Ans.

9.Explain, why does colour of KMn0₄ disappear when oxalic acid is added to its solution in acidic medium?
Ans.

10.Complete the following reactions.

(i)C₆H₅NH₂ + Br₂ (ag) —— >

(ii)C₆H₅NH₂ + (CH₃C0)₂0 —— >

Or

Draw the structures of the different isomers aliphatic amines corresponding to the molecular formula C₃H₉N.

Ans.

                                                          Section C

11.(i) Draw the structure (structural formula) of pyrophosphate ion.
(ii) PH₃ forms bubbles when passed slowly in water but NH₃ dissolves. Explain, why?
Ans.

12.(i) Iron has a body centred cubic cell with a cell edge of 286.5 pm. The density of iron is 7.87 g cm^-3 . Use this information to calculate the Avogadro’s number.[Atomic mass of Fe =56 gmoT¹]
(ii) How does the structure of quartz and quartz glass differ from each other?
Ans.

Ans.

Ans.

Ans.

Ans.

17.Explain the terms.
(i)Electrophoresis (ii) Coagulation (iii) Hardy Schulze law
Ans.(i) Electrophoresis The movement of colloidal particles under the influence of an electric field is called electrophoresis or cataphoresis.Earlier the term used was ‘Cataphoresis because most of the colloidal sols studied at that time contained positively charged colloidal particles and thus migrated towards cathode.
(ii)Coagulation The formation of aggregates or precipitate of colloidal particles by addition of a suitable electrolyte is called coagulation.
For example, in the presence of large excess of the electrolyte the charge on the particles of the dispersed phase is neutralised and as a result, they come closer and grow inside and ultimately forms precipitate.
(iii)Hardy Schulze Law
(a)The effective ions of the electrolyte in bringing about coagulation are those which carry charge opposite to that of the colloidal particles. These ions are called coagulating ions.
(b)Greater is the valency of the coagulating or the flocculating ions, greater is its power to bring about the coagulation.

18.Write down the IUPAC name for each of the following complexes and indicate the oxidation state, electronic configuration and coordination number. Also give stereochemistry and magnetic moment of the complex.
(i) [CrCl₃(Py)₃]           (ii) K₄[Mn(CN)₆]                    (iii) Cs[FeCl₄]
Ans.

19.(i) Explain, why propanol has higher boiling point than that of the hydrocarbon butane?
(ii)Write the mechanism of hydration of ethene to yield ethanol.
Ans.

Ans.

21.(i) How does the presence of double bonds in rubber molecules influence their structures and reactivity?
(ii) Discuss the main purpose of vulcanisation of rubber.
Ans.(i) Natural rubber is c/s-polyisopropene. It is obtained by polymerisation of isoprene units at 1,4 positions. In rubber molecule, double bonds are located between C2 and C3 of each isoprene unit. These c/s-double bonds do not allow the polymer chain to come closer. Therefore, only weak van der Waals’ forces are present. Since, the chains are not linear, they can be stretched just like springs and exhibit elastic properties.

(ii) Vulcanisation of rubber is done due to the following reasons :
(a)It makes rubber wear and tear resistant.
(b)Rubber also becomes resistant to the action of organic acids.
(c)Elasticity of rubber increases and it remains unaffected over a wide range of temperature

22.(i) Name a substance which can be used as an antiseptic as well as disinfectant.
(ii)Name a sweetning agent used in the preparation of sweets for a diabetic patient.
(iii)What are the main constituents of dettol?
Or
(i)Which type of drugs come under antimicrobial drugs?
(ii)What is the harmful effect of hyper acidity?
(iii)Which site of an enzyme is called allosteric site?
Ans.(i) 0.2 % solution of phenol can be used as an antiseptic while its 1% solution can be used as a disinfectant.
(ii)Sucralose (a trichloro derivative of sucrose) or saccharin.
(iii)Chloroxylenol and terpineol.
Or
(i)Antiseptics, antibiotics and disinfectants.
(ii)Ulcer developed in stomach.
(iii)Sites different from active site of enzyme where a molecule can bind and affect the shape of active site is called allosteric site. Some drugs may also bind at this site.

                                                Section D

23.Saxena, head of metallurgical division Based on the above passage, answer the always insisted for refining of copper by  electrolytic method, instead of other  convenient methods, inspite of the fact   that it is power consuming and takes  longer time. Based on the above passage, answer the following questions.
(i)Is electrolytic refining environmental friendly or economical?
(ii) How cathode, anode and electrolyte used in this process?
(iii)Write the values shown by Mr. Saxena.
Ans.(i) Electrolytic refining of copper is environmental friendly but not economical, because this method is power consuming method. Impurities from the impure blister copper deposit as anode mud which contains antimony, selenium, tellurium, silver, gold and platinum. Recovery of these valuable metals may meet the cost of refining.
(ii)At cathode Pure copper strips.At anode Impure blister copper.Electrolyte Aqueous CuS04 solution.
(iii)The values shown by Mr. Saxena are concern about environment pollution and human health.

                                                        Section E

24.A mixture of two aromatic compounds A and B was separated by dissolving it in chloroform followed by the extraction with aqueous KOH solution. The organic layer containing compound A, when heated with alcoholic solution of KOH produced a compound C (C₇H₅N) associated with an unpleasant odour. The alkaline aqueous layer on the other hand, when heated with chloroform and then acidified gave a mixture of two isomeric compounds D and E of molecular formula C₇H₆0₂. Identify the compounds A, B, C, D and E and draw their structures.
Or
Predict the product when cyclohexane carbaldehyde reacts with following reagents.
(i)C₆H₅MgBr followed by H₃0⁺
(ii)Tollen’s reagent
(iii)Semicarbazide in the weakly acidic medium
(iv)Excess of ethanol in the presence of acid
(v)Zinc amalgam and dilute hydrochloric acid
Ans.

25.(i) Considering the parameters such as bond dissociation enthalpy, electron gain enthalpy and hydration enthalpy, compare the oxidising power of F₂ and Cl₂.
(ii) Give two examples to show the anomalous behaviour of fluorine.
Or
On heating, compound A gives a gas B which is a constituent of air. This gas when treated with 3 moles of hydrogen H₂ in the presence of a catalyst gives another gas C which is basic in nature. Gas C on further oxidation in moist condition gives a compound D which is a part of acid rain. Identify compounds A to D and also give necessary equations of all the steps involved
Ans.


(ii) The two anomalous behaviour, of fluorine are as follows:
(a)It forms only one oxoacid while, other halogens form a number of oxoacids.
(b)Flydrogen fluoride (HF) is a liquid (bp 293 K) due to strong hydrogen bonding whereas other hydrogen halides are gases.
Or
The main constituents of air are nitrogen (78%) and oxygen (21%). Only N2 reacts with three moles of H2 in the presence of a catalyst to give NFt3 gas (ammonia) which is basic in nature. On oxidation, NH3 gives N02 which is a part of acid rain.

26.A first order reaction, A—— » B, requires activation energy of 70 kJ mol^-1. When a 20% solution of A was kept at 25°C for 20 minutes, 25% decomposition took place. What will be the per cent decomposition at the same time in a 30% solution maintained at 40°C? Assume that activation energy remains constant in this range of temperature.
Or
(i)Mention the factors that affect the rate of a chemical reaction.
(ii)A reaction is of second order with respect to a reactant. How is the rate of reaction affected if the concentration of the reactant is
(a)doubled?
(b)reduced to half?
(iii)What is the effect of temperature on the rate constant of a reaction? How can this temperature effect on rate constant be represented quantitatively?
Ans.






Or
(i)Factors that affect the rate of a reaction are:
(a)Nature of reactants Ionic substances react more rapidly than covalent compounds because ions produced after dissociation are immediately available for reaction.
(b)Concentration of reactants Rate of a reaction increases when concentration of reactants is increased.
(c)Temperature Generally, rate of a reaction increases on increasing the temperature due to increase in number of collision.
(d)Surface area of the reactants Rate of a reaction increases with increase in surface area of the reactants. That is why, powdered form of reactants is preferred than their granular form.
(e)Catalyst Presence of catalyst also affects the rate
of a reaction. It decreases the activation energy by forming a reaction intermediate and hence, lowers the potential energy barrier. So, rate of a reaction increases.

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