Correct 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.
In CH4, the central atom is C which is in sp3 hybridization state. The four H-atoms are situated at the four corners of the tetrahedron. The bond angle between H—C—H is 109.5° which is called the tetrahedral angle.
But in the case of NH3 and H2O molecules, their central atoms N and O have a lone pair of electrons. This lone pair causes repulsion of electrons and hence causes the decrease in the normal tetrahedral angle which gets reduced to 107° in NH3 and 104.5° in H2O.
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.
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.