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std-12th-perfect-chemistry-1-notes-science-mh-board-solutions-12910 Flipbook PDF
std-12th-perfect-chemistry-1-notes-science-mh-board-solutions-12910
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Chapter 01: Solid State
01
Solid State
Q.1. Refractive index of a solid is observed to have the same value along all directions. Comment on the nature of this solid. Would it show cleavage property? (NCERT) Ans: As the solid has same value of refractive index along all directions, it is isotropic and hence amorphous. Being an amorphous solid, it would not show a clean cleavage when cut with a knife. Instead, it would break into pieces with irregular surfaces. Q.2. Solid A is a very hard electrical insulator in solid as well as in molten state and melts at extremely high temperature. What type of solid is it? (NCERT) Ans: It is a covalent solid such as SiO2, diamond, SiC, AlN, etc. Covalent solids (except graphite) have very high melting point and are insulators. Q.3. What type of solids are electrical conductors, malleable and ductile? Ans: Metallic solids are electrical conductors, malleable and ductile. Q.4. What is the coordination number of atoms: i. in a cubic close-packed structure? ii. in a body-centred cubic structure? Ans: i. The coordination number of atoms in a cubic close-packed structure is twelve. ii. The coordination number of atoms in a body-centred cubic structure is eight. Q.5. Distinguish between face centred and end centred unit cells. Ans: Face centred and end centred unit cells: Face centred unit cell It contains one constituent particle present at the centre of each face, besides the ones present at its corners. ii. A face centred unit cell has 4 atoms per unit cell. iii. Face centred unit cell is present in cubic and orthorhombic crystal systems. eg. Cu, Al, Pt, Au and BaSO4 contain face centred unit cell. i.
(NCERT)
(NCERT)
End centred unit cell It contains one constituent particle present at the centre of any two opposite faces, besides the ones present at its corners. An end centred unit cell has 2 atoms per unit cell. End centred unit cell is present in orthorhombic and monoclinic crystal systems. MgSO4.7H2O and Na2SO4.10H2O contain end centred unit cell.
Q.6. Which of the following lattices has the highest packing efficiency? i. Simple cubic ii. Body centred cubic and iii. Hexagonal close-packed lattice? Ans: Hexagonal close-packed lattice has the highest packing efficiency. Lattice Simple cubic Body centred cubic Hexagonal close-packed
(NCERT)
(NCERT)
Packing efficiency (%) 52.4 68.04 74.0
Q.7. What type of stoichiometric defect is shown by: i. ZnS? ii. KCl? iii. AgBr? Ans: i. ZnS shows Frenkel defect due to a large difference in size of Zn2+ ion and S2 ion. ii. KCl shows Schottky defects, as the size of K+ ion is almost similar to that of Cl ion. iii. AgBr shows both Frenkel defect and Schottky defect.
(NCERT)
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Std. XII Sci.: Perfect Chemistry - I
Solutions and Colligative Properties
Q.1. Give an example of a solid solution in which the solute is a gas. (NCERT) Ans: Adsorption of hydrogen gas by platinum or palladium, pumice stone, etc., is an example of a solid solution in which the solute is a gas. Q.2. Why do gases always tend to be less soluble in liquids as the temperature is raised? (NCERT) Ans: i. The dissolution of a gas in a liquid is an exothermic process and there exists an equilibrium as follows: Dissolved gas, H = ve Liquid + Gas ii. When the temperature is raised, the equilibrium shifts in the backward direction which is in accordance with the Le-Chatelier’s principle. Therefore, the gases always tend to be less soluble in liquids as the temperature is raised. Q.3. The depression in freezing point of water observed for the same amount of acetic acid, trichloroacetic acid and trifluoroacetic acid increases in the order given. Explain briefly. (NCERT) Ans: i. The depression in freezing point of water is in the order: Acetic acid