AHSEC| CLASS 12| CHEMISTRY| CHAPTER - 1| SOLID STATE| SOLVED QUESTIONS FOR 1 MARK EACH| H.S. 2ND YEAR
SOLID STATE
Solved questions for 1 mark each:
(A) VERY SHORT ANSWER:
1. Define the
term amorphous solid.
Ans: Those
substances whose constituent particles are not arranged in any regular
arrangement are called amorphous solids. For example, only short distance order
placement. Such as: glass, rubber, etc.
2. Which
point defects lowers the density of a crystal? [Exam paper – 2015]
Ans: Schottky
defects reduce the density of the crystal.
3. What do
you mean by co-ordination number in an ionic crystal?
Ans: The
number of nearest neighbours of a particle in an ionic crystal is called its
coordination number.
4. How many
atoms can be assigned to its unit cell if an element forms (i) a body centred
cubic (bcc) cell and (ii) a face centred cubic (fcc) cell.
Ans: (i) 2, (ii) 4
5. What is
the co-ordination number of each of ions in a rock salt type crystal structure?
Ans: 6 (six)
6. What type
of substances exhibit antiferromagnetism?
Ans: When
the magnetic moments are aligned such that the magnetic moment becomes zero the
magnetism is called antiferromagnetism. Like, MnO.
7. What is a
bravais lattice?
Ans: There
are only 14 possible three-dimensional lattices. These are called Bravais
lattices and each lattice is called a Bravais lattice.
8. A solid
has the conductivity of
To which category of conductors
does it belong?
Ans: Semiconductors.
9. What are F
centres?
Ans: The
anionic sites occupied by unpaired electrons are called F-centres.
10. Explain
the term anisotrophy.
Ans: Materials
whose physical properties vary in different directions are called anisotropy. E.g.:
Crystalline materials are anisotropic in nature.
11. Classify
the following as being either a p-type or n-type semiconductor:
(i) Ge
doped with In
(ii) B
doped with Si
Ans: (i)
Ge doped with In = p-type
(ii) B doped
with Si = n-type
12. What is
point defect?
Ans: When
deviations or irregularities from the ideal arrangement exist around a point or
atom in a crystalline material, that defect is called a point defect.
13. Why is
Frenkel defect found in AgCl?
Ans: Due
to their small size, Ag+ ions and Zn2+ ions can enter the
interstitial sites. Thus, Frenkel defect was found in AgCl.
14. What
makes alkali metal halides sometimes coloured, which are otherwise colourless?
Ans: The
presence of an F-centre (or colour centre) sometimes makes alkali metal halides
colored which are otherwise colourless.
15. What are
pseudo solids? Give examples.
Ans: Like
liquids, amorphous solids also have a tendency to flow. Therefore, they are
also called pseudo-solids. Example: glass.
16. How is
the unit cell of crystal characterised? How many basic crystal systems are
obtained on the basis of this characterisation?
Ans: Unit
cell of crystal is characterised as:
(a) Its
dimension along the three edges, a, b and c. These edges may or may not be
mutually perpendicular.
(b) Angles
between the edges, α (between b and c). β (between a and c) and
(between a and b). Seven basic crystal systems are obtained on this basis.
17. What type
of crystal defect is produced when sodium chloride is doped with MgCl?
Ans: Impurity defect.
18. What is
the percentage of filled space in the face centred cubic unit cell and body
centred cubic unit cell?
Ans: The
percentage of space occupied in face centered cubic unit cell and body centered
cubic unit cell are 26% and 32% respectively.
19. What type
of lattice imperfections are found in crystals?
Ans: Vacancy
defects and point defects are found in crystals.
20. What is
the effect of Frenkel and Schottky defect on electric conductivity?
Ans: Electrical
conductivity increases due to the presence of Schottky and Frenkel defects. But
due to Frenkel defect the dielectric constant increases due to which the
conductivity reduces to some extent.
21. What are
interstitial defects in a crystal?
Ans: When
some of the constituent particles (atoms and molecules) occupy vacant
interstitial positions, the crystal is said to have interstitial defects.
22. What is
the co-ordination number of an octahedral void?
Ans: The
coordination number of octahedral void is 6.
23. What is
the effect of temperature on the conductivity of semiconductors?
Ans: The
conductivity of semiconductors increases as the temperature increases.
24. Frenkel
defect is not found in halides of a alkali metal. Why?
Ans: Frenkel
defect is not found in alkali metal halides because the ions cannot occupy
interstitial sites.
25. Why does
pure silicon which is an insulator behave as semiconductor on heating?
Ans: The
electrons of pure Si are in the lower energy state. Due to increase in
temperature the electrons move to higher energy states. These electrons move
freely in the crystal and are responsible for electrical conduction. Thus, pure
silicon which is an insulator, behaves as a semiconductor when heated.
26. Define
forbidden zone in the insulator.
Ans: The
space between the valence band and the conduction band represents the forbidden
energy for electrons and is called the energy gap or forbidden region in
insulators.
27. What type
of alignments in crystals make them ferromagnetic?
Ans: The
spontaneous alignment of the magnetic moments of the domains in the same
directions in crystals makes them ferromagnetic.
28. Which
point defect in crystal does not alter the density of the relevant solid?
Ans: Frenkel defect.
29. Which
point defect in crystal alters the density of a solid?
Ans: Vacancy defect.
30. Write a
feature which will distinguish a metallic solid from an ionic solid?
Ans: The
constituent particles in metallic solids are positive ions immersed in a sea of
mobile electrons, but in ionic solids the constituent particles are positively
and negatively charged ions arranged regularly throughout the solid.
31. Name the
non-stoichiometric point defect responsible for colour in alkali metal halides.
Ans: Metal
Excess Defect.
32. What is
photovoltaic cell?
Ans: The
cell which converts solar energy into electrical energy is called photovoltaic
cell.
33. What kind
of attractive forces are present in the molecular crystal solid?
Ans: The
forces present are: (a) dispersion or London force, (b) dipole – dipole
interaction, (c) H-bonding.
34. What is a
unit cell?
Ans: The
unit cell is the smallest part of the crystal lattice which when repeated in
different directions forms the entire lattice.
35. Which
point defects in the crystal unit increases the density of solid?
Ans: Interstitial defect.
36. How many
effective Na* are located at the edge centre of a unit cell in a NaCl crystal.
Ans: 12 Na+ ions.
37. Define
void?
Ans: In
solids, the constituent particles are packed closely together, leaving minimal
void space. This empty space is called void.
38. What is
the number of tetrahedral voids in a unit cell of a cubic close packed
structure?
Ans: 8
tetrahedral voids in a unit cell of ccp structure.
39. Name one
solid in which both Frenkel and Schottky defects occur?
Ans: AgBr
40. How do
metallic and ionic substances differ in conducting electricity?
Ans: Ionic
substances are bad conductors in the solid state but conduct electricity in the
molten state and in aqueous solution.
But metallic
substances conduct electricity in the solid state as well as in the molten
state.
41. What is
the percentage efficiency of packing in case of a simple cubic lattice?
Ans: 52.4%
42. What are
n types semiconductors?
Ans: When
silicon or germanium is mixed with an electron rich impurity like P or A, its
conductivity increases. It is called n-type semiconductor, the rare conduction
is due to the extra electron.
43. Why does
zine oxide exhibit enhanced electrical conductivity on heating?
Ans: On
heating ZnO gives the following reaction
When heated ZnO
exhibits increased electrical conductivity which is due to these trapped
electrons.
44. In NaCl crystal Cl ions are in fcc arrangement Calculate the number of Clion in its unit cell.
45. In CaF2
crystal Ca2+ ion are present fee arrangement. Calculate the number
of F- ion in the unit cell:
Ans: No.
of fluoride ion = 8 (within the body) × 1 = 8.
46. Why is
phosphorus doped silicon a semiconductor?
Ans: If
the result is an n-type semiconductor, phosphorus is added to the silicon.
47. Define
forbidden zone in the insulator.
Ans: The
gap between the filled valence band and the next higher empty band (conduction
band) is large. This is the difference. The forbidden region is called the
insulator. Due to this large gap, electrons cannot move across it and hence the
insulator has very low conductivity.
48. How do
metallic and ionic substances differ in conducting electricity?
Ans: Ionic
substances are bad conductors in the solid state but conduct electricity in the
molten state and in aqueous solution.
But metallic
substances conduct electricity even in solid and molten state.
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