Selected Past II JEE questions - Set 1 (for JEE 2010)

1. Give reasons - two or three sentences

a. Phenyl group is known to exert negative inductive effect. But each phenyl ring in biphenyl (C6H5-C6H5) is more reactive than benzene towards electrophilic substitution.

b. The species [CuCl4]^2- exists while [CuI4]^2- does not.

c. Bond dissociation energy of F2 is less than that of Cl2.

d. Hydrogen peroxide acts an an oxidising as well as a reducing agent.

e. Sulphur dioxide is a more powerful reducing agent in an alkaline medium than in acidic medium.

2. A light bluish green crystalline compound responds to the following tests:

i. Its acqueous solution gives a brown precipitate or coloration with alkaline K2[HgI4] solution.
ii. Its acqueous solution gives a blue colour with K3[Fe(CN)6] solution.
iii. Its solution in hydrochloric acid gives a white precipitate with BaCl2 solution.

Identify the ions present and suggest the formula of the compound.

3. Write tautomeric forms of phenol

4. At 27°C, hydrogen is leaked through a tiny hole into a vessel for 20 minutes. Another unknown gas at the same temperature and pressure as that of H2 is leaked through the same hole for 20 minutes. After the effusion of the gases the mixture exerts a pressure of 6 atmosphere. The hydrogen content of the mixture is 0.7 mole. If the volume of the container is 3 litres, what is the molar mass of the unknown gas.

5. An organic compound 'A' on treatment with ethyl alcohol gives a carboxylic acid 'B', and compound 'C'. Hydrolysis of 'C' under acidic conditions gives 'B' and 'D'. Oxidation of 'D' with KMnO4 also gives 'B'. 'B' on heating with Ca(OH)₂ gives 'E' (molecular formula, C₃H₆O). 'E' does not give Tolleng test and does not reduce Fehling's solution but forms a 2, 4-dinitrophenylhydrazone. Identify 'A', 'B', 'C', 'D', and 'E'.