Bihar Board - Class 12 Chemistry - Chapter 1: The Solid State Short Answer Question
Short Question Answer
Q. 1. Why are solids rigid ?
Answer ⇒ At sufficiently low temperature, the thermal energy is low and intermolecular ions forces between the particles (atomic lows or molecules) of a solid bring them so close that they cling to one another and occupy fixed positions. These can still oscillate to and from about their mean position. Thus solids are rigid.
Q. 2. What is Schottky and Frenkel Defect?
Answer ⇒ (i) Schottky Defect : When the same number of cations and anions are missing in lactic there will be a number change in molecular formulae then this defect is known as Schottky defect.
(ii) Frenkel Defect : In this defect some of cation changes its interstitial (void) position within a unit cell then there will be no changing in molecular formulae as well as in density then there defect is known as frenkel defect.
Q. 3. What makes a glass different from a solid such as quartz ? Under what conditions could quartz be converted into glass ?
Answer ⇒ Quartz is a crystalline form of silica (SiO2). In it SiO4 tetrahedra are connected to one another in such a way that the oxygen atom of each SiO4 a tetrahedron is shared with another silicon atom. If quartz or SiO4 is melted and the melt is cooled, glass is formed which is amorphous. In glass SiO4 tetrahedra are randomly joined. It is a super cooled liquid.
Q. 4. Give the significance of a lattice point.
Answer ⇒ (i) Each point in a lattice is called a lattice site or lattice point.
(ii) Each point in a crystal lattice represents one constituent particle which may be an atom, a molecule or an ion.
(iii) Lattice points are joined by straight lines to bring out the geometry of the lattice.
Q. 5. What type of stoichiometric defect is shown by (i) ZnS, (ii) AgBr.
Answer ⇒ (i) ZnS : It shows the Frankel defect or dislocation defect. It is shown by ionic substances where there is a large difference in the size of the ions.
(ii) AgBr: It shows both Frenkel and Schottky Defect.
Q. 6. Which out of NaCl and CsCl , has a larger coordination number ?
Answer ⇒ CsCl = 8 ; NaCl =6 , ∴ CsCl has a larger coordination number.
Q. 7. In CaF2 crystal, Ca2+ ions present in fcc arrangement Calculate the number of F-ions in the unit cell.
Answer ⇒ No. of Ca2+ ions per unit cell
=8 18 + 6 12=4
Hence, no. fo F-ions per unit cell = 2 4 = 8
Q.8 . Classify the following as amorphous or crystalline solids: Polyurethane, naphthalene, benzoic acid, teflon, potassium nitrate, cellophane, polyvinyl chloride, fiberglass, copper.
Answer ⇒ Crystalline solids: Naphthalene, potassium nitrate, benzoic acid, and copper
Amorphous solids: Polyurethane, cellophane, Teflon, fiberglass and polyvinyl chloride.
Q. 9 . What type of crystal defect is produced when NaCl is doped with MgCl2 ?
Answer ⇒ It is called an impurity defect. A cation vacancy is produced. A substitutional solid solution is formed (because 2Na+ ions are replaced by one Mg2+ ions in the lattice).
Q. 10 . What makes a glass different from a solid such as quartz? Under what conditions could quartz be converted into glass?
Answer ⇒ The arrangement of the constituent particles differentiates glass from quartz. The constituent particles in glass have a short-range order, but the constituent particles of quartz possess long range orders. Quartz is converted into glass by heating it and then rapidly cooling it.
Q. 11. Why is the Frenkel defect not found in pure metal halides ?
Answer ⇒ Because in metal (alkali) halides, ions cannot get into interstitial sites due to their large sizes.
Q. 12. 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?
Answer ⇒ These solids are isotropic in nature i.e., they have the same value of physical properties in all directions. Thus, they also have the same value of refractive index along with all directions. As the solid is amorphous it will not exhibit cleavage property i.e., it will break into pieces with undefined surfaces when cut.
Q. 13. What is a photovoltaic cell ?
Answer ⇒ Amorphous silicon acts as a typical photovoltaic cell in which as a result of sunshine (sunlight) electricity is produced.
Q. 14. How does temperature influence the conductivity of a cell ?
Answer ⇒ Its conductivity increases with increase in temperature.
Q. 15. What is the difference in semiconductor obtained by doping silicon with As or with Ga ?
Answer ⇒ Si produced by doping with As is n-type semiconductor in which flow of current is due to electrons while silicon doped with Ga is a p-type semiconductor in which flow of current is due to positive holes.
Q. 16. For what reason is glass also considered a supercooled liquid?
Answer ⇒ Just like a liquid, glass also flows from top to bottom but very slowly. For this reason, glass is also considered a supercooled liquid.
Q. 17. Why do solids have a definite volume ?
Answer ⇒ For a given mass of a solid, its density has a fixed value. Hence a solid has a definite volume. [ Volume=MassDensity]
Q. 18. What are interstitials in crystals ?
Answer ⇒ Atoms or ions that fill the normal vacant interstitial voids in a crystal are called interstitials.
Q.19 . Why do solids have a definite volume?
Answer ⇒ Intermolecular forces of attraction in a solid is really strong, because of this the molecules of solids have fixed positions. This makes them very rigid, thus giving them definite volumes.
Q.20. Define the term ‘amorphous’. Give a few examples of amorphous solids.
Answer ⇒ Amorphous solids are solids without a regular/definitive arrangement of its constituent particles (ions, atoms or molecules) and they possess something called the short-range order, i.e., a regular and periodically repeating arrangement is seen only over short distances, e.g., rubber, glass.
Q. 21. How can you convert NaCl structure into CsCl structure and vice-versa ?
Answer ⇒ NaCl structure can be converted into CsCl structure by application of pressure, while reverse can be done by heating CsCl to 760 K .
Q. 22. What is meant by superconductivity ?
Answer ⇒ At low temperature when a substance offers no resistance to the flow of electricity, the phenomenon is known as superconductivity.
Q. 23. What is the energy gap in band theory ? compare its size in conductors, semi-conductor and insulators ?
Answer ⇒ Energy gap in band theory means the gap of energy between valence band and conduction band. The gap is in order conductor < semiconductor < insulator.
Q. 24. What is an F-center ?
Answer ⇒ The site where electrons are entrapped in the anion vacancy is called F-center.
Q. 25. What happens when ferrimagnetic Fe3O4 is heated to 850 K and Why ?
Answer ⇒ Ferrimagnetic Fe3O4 on heating to 850 K becomes Paramagnetic. This is due to greater alignment of spins in one direction on heating.
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