CBSE Previous Year Solved Papers Class 12 Chemistry Outside Delhi 2014
Time allowed: 3 hours Maximum Marks: 70
- All questions are compulsory.
- Questions number 1 to 5 are very short-answer questions and carry 1 mark each.
- Questions number 6 to 10 are short-answer questions and carry 2 marks each.
- Questions number 11 to 22 are also short-answer questions and carry 3 marks each.
- Questions number 23 is a value based question and carry 4 marks.
- Questions number 24 to 26 are long-answer questions and carry 5 marks each.
- Use log tables, if necessary. Use of calculators is not allowed.
Question.1. What is the effect of temperature on chemisorption ?
Answer : Chemisorption initially increases then’ decreases with rise in temperature. The initial increase is due to the high energy of activation and the decrease afterwards is due to the exothermic nature of adsorption equilibrium.
Question.2. What is the role of zinc metal in the extraction of silver ?
Answer : Zinc is used as a reducing agent to recover silver from its cyanide complex. It reduces Ag+ to Ag and itself get oxidised to Zn2+.
Question.3. What is the basicity of H3PO3 ?
Answer : The H3PO3 ionises to give two H+ ions. Its basicity is two.
Question.4. Identify the chiral molecule in the following pair :
Question.5. Which of the following is a natural polymer? Buna-S, Proteins, PVC
Answer : Protein, is a natural polymer having amino acid as a monomer.
Question.6. The conversion of primary aromatic amines into diazonium salts is known as ——.
Answer : Diazotisation reaction.
Question.7. What are the products of hydrolysis of sucrose?
Answer : The products of Hydrolysis of sucrose are : Glucose and Fructose
Question.8. Write the structure of p-methylbenzaldehyde.
Question.9. An element with density 2.8 g cm-3 forms a F.C.C. unit cell with edge length 4 x 10-8cm. Calculate the molar mass of the element. (Given NA = 6.022 x 1023 mol-1)
Question.10. (i) What type of non-stoichiometric point defect is responsible for the pink colour of LiCl?
(ii) What type of stoichiometric defect is shown bv NaCl?
How will you distinguish between the following pairs of terms?
(i) Tetrahedral and octahedral voids
(ii) Crystal lattice and unit cell
Answer : (i) Metal excess defect due to anionic vacancies is responsible for pink colour of LiCl
(ii) Schottky defect is shown by NaCl.
Question.11. State the Kohlrausch law of independent migration of ions. Why does the conductivity of a solution decrease with dilution?
Answer : It states that the limiting molar conductirily of an eledrolyte can be expressed as sum of individual contribution of anion and cation of the electrolyte.
With dilution, the number of ions per unit volume of electrolyte decrease and hence, conductivity decreases.
Question.12. For a chemical reaction R—>P, of solution the variation in the concentration (R) Vs. time (t) plot is given as
(i) Predict the order of the reaction.
(ii) What is the slope of the curve?
Answer : (i) zero order reaction
(ii) Slope of the curve is (-K). i.e., negative slope.
Question.13. Explain the principle of the method of electrolytic refining of metals. Give one example.
Answer : In electrolytic method, the impure metal is made to act as anode. A strip of the same; metal in pure form is used as cathode. They are put in a suitable electrolytic bath containing soluble salt of the same metal. The more basic metal remains in the solution and the less basic ones go to the anode mud.
For e.g. : Copper is refined using an electrolytic method, the net result of electrolysis is the transfer of copper in pure form from the anode to the cathode.
Anode : Cu ——>Cu2+ + 2e–
Cathode : Cu2+ + 2e– ——> Cu
Question.14. Complete the following equations:
(i) P4 + H2O —–>
(ii) XeF4 + 02F2 —–>
Answer : (i) P4+ H20 —> No reaction.
(ii) XeF4 + O2F2 —> XeF6 + O2
Question.15. Draw the structures of the following: (i) XeF2 (ii) BrF3
Question.16. Write the equations involved in the following reactions:
(i) Reimer-Tiemann reaction
(ii) Williamson synthesis
Answer : (i) Reimer Tiemann reaction :
Question.17. Write the mechanism of the following reaction :
Question.18. Write the name of monomers used for getting the following polymers:
(i) Bakelite (ii) Neoprene
Answer: (i) Phenol and formaldehyde are the monomer used for getting Bakelite.
(ii) Chloroprene is the monomer used to get Neoprene.
Question.20. The following data were obtained during the first order thermal decomposition of S02Cl2 at a constant volume :
Calculate the rate constant. (Given : log 4 = 0.6021, log 2 =log 2 = 0.3010)
Question.21. What are emulsions? What are their different types? Give one example of each type.
Answer : Emulsions are colloids in which both the dispersed phase and dispersing medium are liquid. It is a mixture of two or more liquids that are normally immiscible. They are of two types :
(i) Oil in water type emulsions (O/W) : In such emulsions, oil is the dispersed phase and water is the dispersed medium, e.g. Milk, Vanishing cream.
(ii) Water in oil type emulsions (W/O) : In such emulsions, water is the dispersed phase and oil is the dispersed medium, e.g. Butter, Cod liver oil.
Question.22. Given reasons for the following:
(i) (CH3)3 P = O exists but (CH3)3N = O does not.
(ii) Oxygen has less electron gain enthalpy with negative sign than sulphur.
(iii) H3P02 is a stronger reducing agent than H3P03.
Answer : (i) Due to the absence of d-orbitals, nitrogen cannot form pπ-dπ multiple bonds. Thus, N cannot expand its covalency beyond four. So, the compound (CH3)3N= O does not exist. On the other hand, P due to the presence of (7-orbitals forms, pπ-dπ multiple bonds and hence forms (CH3)3P = O in which covalency of P is 5.
(ii) Due to small size and high electro negativity of oxygen compared to sulphur, oxygen has less electron gain enthalpy.
(iii) Acids which contain P-H bonds have reducing character, Since H3PO2 contains two P-H bonds while H3 P03 contains only one P-H bond therefore, H3P02 is a stronger reducing agent than H3PO3.
Question.23. (i) Write the IUPAC name of the complex [Cr(NH3)4Cl2] Cl.
(ii) What type of isomerism is exhibited by the complex [Co(en)3]3+?
(en = ethane-1,2-diamine)
(iii) Why is [N1Cl4]2- paramagnetic but [Ni(CO)4] is diamagnetic
(At. nos.: Cr = 24, Co = 27, Ni = 28)
Answer: (i) Tetraammine dichlorido chromium(III) chloride
(ii) Optical isomerism is shown by the complex [CO(en)3]3+
(iii) [Ni(Cl)4]2-, Ni is in +2 oxidation state with the electronic configuration 3d84s0. As Cl– is a weak ligand it cannot pair up the electrons in 3d orbitals therefore, [NiCl4]2- is paramagnetic. In [Ni(CO)4], Ni is in O oxidation state with the electronic configuration 3d84s2. Co is a strong ligand it causes As electrons to shift to id and pair up id electrons. Therefore, Ni(CO)4 is diamagnetic.
Question.24. (a) Draw the structure of major monohalo products ii each of the following reactions :
(b) Which halogen compound in each of the following pairs will react faster in SN2 reaction:
(i) CH3Br or CH3I
(ii) (CH3)3C-Cl or CH3-Cl
(b) (i) CH3-I will react faster because I-is better leaving group.
(ii) CH3-CI will react faster because it is a primary halide and they undergo SN2 reaction faster.
Question.25. Account for the following:
(i) Primary amines (R-NH2) have higher boiling point than tertiary amines (R3N).
(ii) Aniline does not undergo Friedel-Crafts reaction.
(iii) (CH3)2NH is more basic than (CH3)3N in an aqueous solution.
Give the structures of A, B and C in the following reactions :
Answer : (i) Due to intermolecular hydrogen bonding in primary amines (presence of more number of H-atoms). They have high boiling point in comparison to tertiary amines.
(ii) Aniline does not undergo Friedel-Crafts reaction because Aniline is basic in nature reacts with AlCl3 to form a salt. The positive charge on the N-atom, electrophilic substitution in the benzene ring is deactivated.
Question.26. Define the following terms related to proteins :
(i) Peptide linkage
(ii) Primary structure
Answer : (i) Peptide linkage is the amide linkage -COOH group of one α-amino acid and -NH2 group of other a-amino acid by lose of a water molecule.
(ii) The sequence in which various amino acids are arranged ” in a linear structure with no intermediate bonding is called primary structure of a protein.
(iii) When a protein in its native form is subjected to a change, such as temperature, pit, etc. Due to this protein coss its biological activity is called denaturation of a protein e.g. curdling of.
Question.27. On the occasion ofWorld Health Day, Dr. Satpal organized a ‘health camp’ for the poor farmers living in a nearby village. After check-up, he was shocked to see that most of the farmers suffered from cancer due to regular exposure to pesticides and many were diabetic. They distributed free medicines to them. Dr. Satpal immediately reported the matter to the National Human Rights Commission (NHRC). On the suggestions of NHRC, the government decided to provide medical care, financial assistance, setting up of super-speciality hospitals for treatment and prevention of the deadly disease in the affected villages all over India.
(i) Write the values shown by (a) Dr. Satpal (b) NHRC?
(ii) What type of analgesics are chiefly used for the relief of pains of terminal cancer?
(iii) Give an example of artificial sweetener that could have been recommended to diabetic patients.
Answer : (i)(a) Dr. Satpaf is caring and compassionate for the farmers of the village. He distributed free medicines to them, (b) NHRC is also compassionate towards the farmers and appreciated Dr. Satpal’s work.
(ii) Narcotic analgesics like morphine and heroin.
Question.28. (a) Define the following terms :
(i) Molarity (ii) Molal elevation constant (kb)
(b) A solution containing 15 g urea (molar mass = 60 g mol-1) per litre of solution in water has the same osmotic pressure (isotonic) as a solution of glucose (molar mass = 190 g mol-1) in water. Calculate the mass of glucose present in one litre of its solution.
(a) What type of deviation is shown by a mixture of ethanol and acetone? Give reason.
(b) A solution of glucose (molar mass = 180 g mol-1) in water is labelled as 10% (by mass). What would be the molality and molarity of the solution? (Density of solution = 1.2 g mL-1)
Answer : (a) (i) The number of moles of a solute present in one litre of solution is known as its molarity.
The elevation in boiling point of a solution when one mole of non-volatile solute is dissolved in one kilogram of a volatite solvent is known as molal elevation constant (Kb).
(a) The mixture of ethanol and acetone shows positive deviation from Raoults law. In pure ethanol hydrogen bond exist between the molecules. On adding acetone to ethanol, acetone molecules get in between the molecules of ethanol thus breaking some of the hydrogen bonds and weakening molecular interactions leads to increase in vapour pressure , resulting in positive deviation from Raoulr’s law.
(b) (i) Zinc has 3d104s2 configuration with no unpaired d-orbital electron and hence it is not considered as a transition element.
(ii) Transition metals have vacant orbitals to accommodate lone pairs of electrons for bond formation and have high charge density, therefore, they form complexes.
(iii) Due to high stability of Mn-2+ (due to its half-filled 3d sub shell) than Mn3+ while Cr3+ is more stable than Cr2+.
Question.30. (a) Write the products formed when CH3CHO reacts with the following reagents:
(i) HCN (ii) H2N-OH
(iii) CH3CHO in the presence of dilute NaOH
(b) Give simple chemical tests to distinguish between the following pairs of compounds.
(i) Benzoic acid and.Phenol
(ii) Propanal and Propanone.
(a) Account for the following:
(i) Cl–CH2COOH is a stronger acid than CH3COOH.
(ii) Carboxylic acids do not give reactions of carbonyl group.
(b) Write the chemical equations to illustrate the following name reactions:
(i) Rosenmund reduction
(ii) Cannizzaro’s reaction
(c) Out of CH3CH2-CO-CH3 and GH3CH2-CH2– CO-CH3, which give iodoform test?
Answer : (a) (i) On reaction of acetaldehyele with hydrogen cyanide it gives 2-Hydroxypropaneriitrile as product.
Note: Except for the following questions, all the remaining question have been asked in previous set.
Question.1.Why is adsorption always exothermic?
Answer : Adsorption being a surface phenomenon leads to decrease in surface energy and hence is exothermic.
Question.2. Name the method used for refining of Nickel.
Answer: Mond’s process used for refining of Nickel.
Question.3. Why does NO2 dimerise?
Answer : NO2 is an odd-electron molecule and hence dimerises to N2O4.
Question.4. Based on molecular forces, What type of polymer is neoprene?
Answer: Elastomer. .
Question.5. What are the products of hydrolysis of maltose?
Answer : Two units a-D-glucose
Question.6. Write the structure of 4-chloropentan-2 one.
Question.9. Write the name of monomers used for getting the following polymers:
(i) Terelyne (ii) Nylon-6, 6
Answer : (i) Ethylene glycol and terephthalic acid.
(ii) Adipic acid and hexamethylene diamine.
Question.10. Describe the role of the following:
(i) SiO2 in the extraction of copper from copper matte.
(ii) NaCN in froth floatation process.
Answer : (i) SiO2 (Silica) acts as a flux in the extraction of copper from copper matte to remove ferrous oxide as ferrous silicate slag.
FeO + SiO2 —> FeSiCO3 , (Slag)
(ii) NaCN is used as a depressant as it forms-zinc complex, Na2[Zn(CN)4] on the surface of ZnS thereby preventing it from forming froth.
Question.11. Complete the following equations :
(i) Ag + PCl5
(ii) CaF2 + H2SO4
Answer: (i) 2Ag + PCl5 —> 2AgCl + PCl3
(ii) CaF2 +H2SO4 —> CaSO4 + 2HF
Question.12. Draw the structures of the following:
Question.13. (i) Write the type of magnetism observed when the magnetic moment are oppositely aligned and cancel out each other.
(ii) Which stoichiometric defect does not change the density of the crystal?
Answer: (i) Antiferromagnetism observed when the magnetic moment are oppositely aligned and cameal out each other.
(ii) Frenkel defect does not change the density of the crystal.
Question.14. Define the following terms :
(ii) Limiting molar conductivity
Answer: (i) Fuel cell is a device that converts chemical energy from combustion of a fuel into electric energy through a chemical reaction.
(ii) Molar conductivity of electrilyte at infinite dilution or when consentration approaches zero is‘called limiting molar conductivity. It is expressed as
Question.19. Define the following terms :
(i) Glycosidic linkage
(ii) Invert sugar
(iii) Oligo saccharides
Answer : (i) The linkage between two monosaceharide through oxygen atom in an oligosaccharide ora polysaccharide is known as glycosidic linkage.
(ii) Sucrose is called invert sugar as it produces equimolar quantities of glucose and fructose on hydrolysis it gives an equimolar mixture of D – (+)- glucose, and D -fructose, which is laevo rotatory. This change of specific rotation from dextrorotation to laevo-rotation is called inversion-1 of sugar and the mixture is obtained is called invert sugar.
(iii) Carbohydrate which .on hydrolysis give two to ten molecules of monosaccharides are called oligosaccharide e.g. sucrose.
Note: Except for the following questions, all the remaining question have been asked in previous sets.
Question.1. What are the dispersed phase and dispersion medium in milk?
Answer : Dispersed phase is oil or fat and dispersion medium is water.
Question.2. Name the method used for refining of copper metal.
Answer: Electrolytic refining.
Question.3. Why does NH3 act as a Lewis base?
Answer : Due to the presence of lone pair on nitrogen in NH3, it forms coordinate bonds with Lewis acids and acts as Lewis base.
Question.5. Which of the following is a fibre? Nylon, Neoprene, PVC.
Question.6. Write the products of hydrolysis of lactose.
Question.8. Write the structure of 2-hydroxybenzoic acid.
Question.9. Complete the following equations :
(i) Cu + 2H2SO4 (Cone.) —> CuSO4+ SO2+ 2H2O
(ii) XeF2 + H2O
(i) Cu + cone 2H2SO4 —-> CuSO4 + SO2+ 2H20
(ii) 2XeF2 + 2H20 —–> 2Xe + 4HF + O2
Question.10. Draw the structure of the following:
Question.11. Write the name of monomers used for getting the following polymers:
(i) Teflon (ii) Buna-N
Answer: (i) Tetrafluoroethene
(ii) Butadiene and acrylonitrile
Question.13. (i) Write the type of magnetism observed when the magnetic moment are aligned in parallel and anti-parallel directions in unequal numbers.
(ii) Which stoichiometric defect decreases the density of the crystal?
Answer: (i) Ferrimagnetism.
(ii) Schottky defect decreases the density of the crystal.
Question.14. Define the following terms :
(i) Molar conductivity
(ii) Secondary batteries
Answer : (i) Molar conductivity is defined as the conducting power of all the ions produce by dissolving one more of an electrolyte in solution.
(ii) Secondary batteries are those batteries which can be recharged by passing electric current through them and hence can be used over again e.g. Lead storage battery.
Question.17. Write the principle behind the froth floatation process. What is the role of collectors in this process?
Answer: Froth floatation method has been in use for removing gangue from sulphide ores. In this process, a suspension of the powdered ore is made with water.
Collectors (e.g. pine oils, fatty acids, etc.) enhance non-wettability of the mineral particles and used to skim the froth off the surface.
Question.23. Define the following terms :
(iii) Essential amino acids
Answer: (i) A Nucleotide contain all the three basic components of nucleic acid i.e., apentose sugar, a nitrogeneous base and a phosphoric acid. When nucleoside is linked to phosphoric acid at 5′ position of sugar moiety, we get a nucleotide, (ii) The carbohydrate which differ in configuration at the glycosidic carbon ( i.e., C1 in aldoses and in ketoses) are called anomers. e.g. α -D-(+) glucose and β-D-(+) glucose, (iii) Those amino acids which cannot be synthesised by the body and need to be consumed through diet. eg. Valine.