The pattern in which the question papers are being set for a particular subject is quite different from the manner in which the course structure is defined actually. Though the course curriculum is predefined, there are certainly some gaps between the question paper formed and the content of the course. Henceforth, students need to identify these gaps and catch up where the textbooks left off, if they want to get acquainted with the examination pattern. And, they can do it easily by checking out previous year question papers and their solutions. This not only helps them prepare for exams in a better manner but also leads them to the depth which the topic should be studied with.
Some solved questions from CBSE Class 12th Chemistry Question Paper 2011-Set III, are given here
Q. What is meant by an æintrinsic semiconductorÆ?
Ans. In semiconductors, the gap between the valence band and conduction band is small. Because of which, some electrons jump to conduction band and show some conductivity. Electrical conductivity of semiconductors increases with rise in temperature, since more electrons can jump to the conduction band. These substances are called as intrinsic semiconductors. For example- silicon and germanium
Q. What do you understand by ædenticity of a ligandÆ?
Ans. When a polydentate ligand uses its two or more donor atoms to bind a single metal ion, it is said to be a chelate ligand. The number of such ligating groups is called the denticity of the ligand. For example -
Q. Which will react faster in SN2 displacement, 1-bromopentane or 2-bromopentane, and why?
Ans. 1-bromopentane will react faster in SN2 displacement. As we know, this reaction requires the approach of the nucleophile to the carbon bearing the leaving group, the presence of bulky substituents on or near the carbon atom have a inhibiting effect.
Q. Why is an alkylamine more basic than ammonia?
Ans. The basicity of amines depends on the +I effect of the alkyl groups. In alkylamine, -CH3 groups increase the electron density on the nitrogen atom and thus increases the basicity whereas in ammonia - CH3 groups are absent. Thus, alkylamine is more basic than ammonia