12th Class Chemistry Sample Paper - 5
Time Allowed: 3 hours
Maximum Marks: 70
(a) All questions are compulsory.
(b) Question numbers 1 to 5 are very short answer questions and carry 1 mark each.
(c) Question numbers. 6 to 10 are short answer questions and carry 2 marks each.
(d) Question numbers 11 to 22 are also short answer questions and carry 3 marks
(e) Question number 23 carries 4 marks.
(f) Question numbers. 24 to 26 are long answer questions and carry 5 marks each
1.Mention two properties of acetonitrile because of which it acts as good solvent.
2.Name a substance which on addition to AgCL causes cation vacancy in it.
3.Mention a large scale use of the phenomenon called ‘reverse osmosis’.
4.Mention two properties of acetonitrile because of which it acts as a good solvent.
5.What is the effect of temperature on chemisorption ?
6.State Kohlrausch law of independent migration of ions. Why does the conductivity of a solution decrease with dilution?
7.Write the mechanism of the following reaction:
8. The freezing point of benzene decreases by 2.12 K when 2.5 g of benzoic acid (C6H5COOH) is dissolved in 25 g of benzene. If benzoic acid forms a dimer in benzene, calculate the van’t Hoff factor and the percentage association of benzoic acid. (Kf for benzene = 5.12 K kg mol-1)
9. Draw a diagram, showing the formation of bonding and ant bonding molecular orbitals by the LCAO in homonuclear hydrogen molecule.
10. The conductivity of 10-3 mol /L acetic acid at 250C is 4.1 × 10-5 S cm-1. Calculate its degree of dissociation, if Λm for acetic acid at 250C is 390.5 S cm2 mol-1.
11. Give reason:
i. PCl5 acts as an oxidising agent.
ii. Dinitrogen is chemically inert.
12. Discuss the magnetic behavior of [Fe(CN)6]3- and [FeF6]3-.
13. Give the IUPAC name of the product formed when:
(i) 2-Methyl-1-bromopropane is treated with sodium in the presence of dry ether.
(ii) 1- Methyl cyclohexene is treated with HI.
(iii) Chloroethane is treated with silver nitrite.
14. Calculate the density of silver which crystallizes in the face-centered cubic structure. The distance between the nearest silver atoms in this structure in 287pm.
(Molar mass of Ag=107.87 g mol-1 , NA=6.02*1023 mol-1 )
15. Describe how the following steps can be carried out?
(a) Recovery of Gold from leached gold metal complex.
(b) Conversion of Zirconium iodide to pure Zirconium.
(c) Formation of slag in the extraction of copper.
(Write the chemical equations also for the reactions involved)
16. How potassium dichromate is prepared from chromite ore? Give ionic equation when acidic solution of potassium dichromate reacts with sodium sulphite.
17. What is stereospecific reaction? Give two examples of this reaction.
18. Describe the following in brief:
i. Carbon dating
ii. Thermonuclear reactions
iii. Group displacement law
19. Explain the following terms with suitable examples:
ii. n-type semiconductor
iii. Forbidden zone
20. Give reasons:
i. Ketones are less reactive towards nulceophiles than aldehydes.
ii. Benzoic acid is stronger acid than ethanoic acid.
21. Explain the following giving one example of each:
i. Vat dyes.
iii. Hybrid rocket propellants.
22. Describe the following with suitable examples:
iii. Hybrid propellants
23. The radius of a spherical ball of copper is 3.5cm.Its outer surface is to be coated with silver. Calculate the time, if the thickness of silver layer is 0.02mm and as steady current of 1.1 ampere is passed through an electrolytic solution of silver nitrate .(density of silver =10.6g mL-1) and atomic mass of silver = 108 mu).
24. An aromatic compound ‘A’ (C8H6) reacts with dil. H2SO4and HgSO4 giving ‘B’, which upon reaction with NaOH and I2 gives compounds ‘C’ and ‘D’. ‘D’ upon reaction with soda lime gives a hydrocarbon ‘E’, which on reaction with CH3COCl in the presence of anhydrous aluminum chloride gives ‘B’. Identify ‘A’, ‘B’, ‘C’, ‘D’ and ‘E’ and write the equations of the reactions involved.
Ozonolysis of compound ‘A’ (C7H14) yields a mixture containing compounds ‘B’ and ‘C’.Both ‘B’ and ‘C’ give positive 2.4 - DNP test and Tollen’s test. ‘B’ undergoes Cannizzaro’s reaction. ‘C’ undergoes aldol condensation to give ‘D’. ‘B’ is also obtained by the reaction of 2, 2 –dimethylpropanol with PCC. Deduce the structures of A, B, C and D and justify your answer by giving the equations of the reactions involved.
25. (a) Why osmotic pressure is a better criteria for measuring the molecular mass of macro-molecules as compared to elevation of boiling point or depression of freezing point?
(b) At 300K, 36g of glucose present in one litre of its solution has an osmotic pressure of 4.98 bar. If the osmotic pressure of the solution is 1.52 bar at the same temperature, what would be its concentration?
(a) An aqueous solution containing 4% nonvolatile solute exerts a pressure of 1.002 bar at the normal boiling point of the solvent. What is the molar mass of the solute?
(b) Why is common salt used to clear the snow off the road?
(c) Why does water stop boiling when sugar is added to it when it is boiling?
26. Discuss the method of extraction of iron from its ore with the help of equations and diagram. Also discuss the thermodynamic principle of the reduction of its oxide into metal.
The choice of reducing agent in a particular case depends on thermodynamic principles. How far do you agree with this statement? Explain the feasibility of the following reduction reactions on the bases of thermodynamic principles.
i. Reduction of Al2O3 with CO
ii. Reduction of Fe2O33 with CO
Given Δ G° (Al(s), Al2O3) = +1582 KJ mol-1
Δ G° (CO(g), CO2(g) = –257.2 KJ mol-1
Δ G° (Fe(s), Fe2O3(s) = +742.2 KJ mol-1