Find CBSE Class 12 Chemistry Solved Practice Paper (Set-IV) for the coming half yearly exam. These questions will not only help the students to prepare for exams in a better manner, but will also help them in understanding the depth with which a topic should be studied.
Few Sample Questions from this paper are as follows:
Q. Define Electrophoresis.
Ans. Electrophoresis is the phenomenon of movement of colloidal particles under the applied electric potential.
Q. Why does the electrical conductivity of semiconductors increase with rise in temperature?
Ans. In case of semiconductors the gap between the conduction band and the valence band is small. Therefore, on increasing the temperature, electrons can easily jump from valence band to the conduction band thereby causing an increase in the conductivity of the semiconductor.
Q. Why is white phosphorous kept under water?
Ans. Due to the angle strain and weraker forces of attraction, ignition temperature of white phosphorous is very low due to which it spontaneously catches fire when exposed to air. Therefore to protect it from air, it is kept under water.
Q. Alkyl halides, though polar, are immiscible with water. Explain why?
Ans. For a substance needs to be miscible with water, the solute-water force or attraction must be stronger than the solute-solute and water-water forces of attraction. In case of alkyl halides which are polar in nature, held together by dipole-dipole interactions. Similarly, strong Hydrogen-bonds exist between the water molecules. The new force of attraction which arises in between the alkyl halides and water molecules is weaker than the alkyl halide-alkyl halide and water-water forces of attraction. Hence, alkyl halides are immiscible with water.
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