Short Answer TypeCorrect the following statements :
Graphite has a two-dimensional sheet-like structure in which each carbon atom is sp3 hybridized.
Correct the following statements :
For water-system, the number of phases that can exist in equilibrium is two.
Radium has a half-life of 1580 years. How long would it take for each of the samples of radium given below to disintegrate ?
(i) 20% of a 5 g sample.
(ii) 20% of a 50 g sample.
Ionic crystal :
1. They are hard and brittle.
2. They have high melting and boiling points.
3. They have high density.
4. They are poor conductors of heat and electricity in solid state.
5. They are highly soluble in water and other polar solvents but almost insoluble in nonpolar solvents (i.e. organic solvents).
Example: NaCl, BaSO4etc.
Network type (Covalent) crystal :
1. They are very hard due to presence of strong covalent bonds.
2. They have very high melting points.
3. They are poor conductors of heat and electricity.
4. They have high heat of fusion.
Examples : Diamond, silicon carbide etc.
For the cell
Zn | Zn2+ (a = 1) | | Cu2+ (a = 1) | Cu
Given that EZn . Zn2+ = +0.761 volt; Ecu2+, Cu = +0.339 volt
(i) Write the cell reaction
(ii) Calculate the emf and free energy change at 298 K involved in the cell. [Faraday’s constant F = 96500 coulomb equivalent– 1].
(i) What is the physical significance of entropy ?
(ii) How is the entropy of the universe changing ?
For the extraction of aluminium, write
(i) The most important ore.
(ii) One method for the purification of the mentioned ore.
(iii) The role of cryolite and calcium fluoride in electrolysis.
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