Chemistry

The Solid State

Question:

Match the type of-packing given in Column I with the items given in Column II.
ncert-exemplar-problems-class-12-chemistry-solid-state-45

Answer:

(i) —> (c); (ii) —> (a); (iii) —>(d); (iv) —> (b)
(i) Square close packing in two dimensions each sphere have coordination number 4, as shown below.
ncert-exemplar-problems-class-12-chemistry-solid-state-46
(ii) Hexagonal close packing in two dimensions each sphere has coordina ¬tion number 6 as shown below and creates a triangular void
ncert-exemplar-problems-class-12-chemistry-solid-state-47
(iii)Hexagonal close packing in 3 dimensions is a repeated pattern of sphere in alternate layers also known as ABAB pattern
ncert-exemplar-problems-class-12-chemistry-solid-state-48
(iv) Cubic close packing in a 3 dimensions is a repeating pattern of sphere in every fourth layer.
ncert-exemplar-problems-class-12-chemistry-solid-state-49

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The Solid State

Q 1.

Explain why does conductivity of germanium crystals increase on doping with gallium?

Q 2.

What is the coordination number in a square close packed structure in two dimensions?  (a) 2 (b) 3 (c) 4 (d) 6

Q 3.

If NaCI is doped with 10-3 mol % SrCl2, what is the concentration of cation vacancies?

Q 4.

Silver crystallises in fcc lattice. If edge length of the cell is 4.07 x 10-8 cm and density is 10.5 g cm-3, calculate the atomic mass of silver.

Q 5.

Assertion (A): The packing efficiency is maximum for the fee structure. Reason (R): The coordination number is 12 in fee structures.

Q 6.

What type of defect can arise when a solid is heated? Which physical property is affected by it and in what way?

Q 7.

Classify each of the following solids as ionic, metallic, modular, network (covalent), or amorphous:
(i) Tetra phosphorus decoxide (P4O10) (ii) Ammonium phosphate, (NH4)3PO4 (iii) SiC (iv) I2 (v) P(vii) Graphite (viii), Brass (ix) Rb (x) LiBr (xi) Si

Q 8.

What type of defect can arise when a solid is heated? Which physical property is affected by it and in what way?

Q 9.

Which of the following statements are true about metals?
(a) Valence band overlap with conduction band
(b) The gap between valence band and conduction band is negligible
(c) The gap between valence band and conduction band cannot be determined
(d) Valence band may remain partially filled.

Q 10.

Copper crystallises into a fee lattice with edge length 3.61 x 10-8 cm. Show that the calculated density is in agreement with its measured value of 8.92 gcm-3.

Q 11.

The total number of tetrahedral voids in the face centered unit cell is
(a) 6 (c) 10
(b) 8 (d) 12

Q 12.

Which of the following statement is not true about the hexagonal close packing?
(a) The coordination number is 12
(b) It has 74% packing efficiency
(c) Tetrahedral voids of the second layer are covered by the spheres of the third layer
(d) In this arrangement, spheres of the fourth layer are exactly aligned with those of the first layer.

Q 13.

The number of tetrahedral voids per unit cell in NaCl crystal is
(c) twice the number of octahedral voids
(d) four times the number of octahedral voids

Q 14.

 A compound forms hexagonal close-packed. structure. What is the total number of voids in 0. 5 mol of it? How many of these are tetrahedral voids?

Q 15.

Non-stoichiometric cuprous oxide, Cu2O can be prepared in laboratory. In this oxide, copper to oxygen ratio is slightly less than 2:1. Can you account for the fact that this substance is a p-type semiconductor?

Q 16.

Why are solids rigid?

Q 17.

Why is glass considered a supercooled liquid?

Q 18.

Why is FeO(s) not formed in stoichiometric composition?

Q 19.

Assertion (A): Total number of octahedral voids present in unit cell of cubic close packing including the one that is present at the body centre, is four. Reason (R): Besides the body centre, there is one octahedral void present at the centre of each ofthe six faces of the unit cell and each of which is shared between two adjacent unit cells.

Q 20.

Explain how vacancies are introduced in an ionic solid when a cation of higher valence is added as an impurity in it.

Q 21.

Gold (atomic radius = 0.144 nm) crystallises in a face centred unit cell. What is the length of the side of the unit cell ?

Q 22.

Why do solids have a definite volume?

Q 23.

What type of solids are electrical conductors, malleable and ductile?

Q 24.

A compound forms hexagonal close-packed. structure. What is the total number of voids in  0. 5 mol of it? How many of these are tetrahedral voids?

Q 25.

Ionic solids, which have anionic vacancies due to metal excess defect, develop colour. Explain with the help of a suitable example.

Q 26.

(i) What is meant by the term coordination number’?
(ii) What is the coordination number of atom
(a) in a cubic close-packed structure?
(b) in a body centred cubic structure?

Q 27.

Silver crystallises in fcc lattice. If edge length of the cell is 4.07 x 10-8 cm and density is 10.5 g cm-3, calculate the atomic mass of silver.

Q 28.

If the radius of the octahedral void is r and radius of the atoms in close-packing is R, derive relation between rand R.

Q 29.

Which of the following is not a characteristic of a crystalline solid?
(a) Definite and characteristic heat of fusion
(b) Isotropic nature
(c) A regular periodically repeated pattern of arrangement of constituent particles in the entire crystal
(d) A true solid

Q 30.

Which of the following represents correct order of conductivity in solids?
ncert-exemplar-problems-class-12-chemistry-solid-state-22

Q 31.

Which of the following statements are not true?
(a) Vacancy defect results in a decrease in the density of the substance
(b) Interstitial defects results in an increase in the density of the substance
(c) Impurity defect has no effect on the density of the substance
(d) Frenkel defect results in an increase in the density of the substance

Q 32.

Which of the following statements are true about semiconductors?
(a) Silicon doped with an electron rich impurity is a p-type semiconductor
(b) Silicon doped with an electron rich impurity is an n-type semiconductor
(c) Delocalised electrons increase the conductivity of doped silicon
(d) An electron vacancy increases the conductivity of type semiconductor

Q 33.

Amorphous solids can also be called
(a) pseudo solids (b) true solids
(c) super cooled liquids (d) super cooled solids

Q 34.

A perfect crystal of silicon (fig) is doped with some elements as given in the options. Which of these options show n-type semiconductors?
ncert-exemplar-problems-class-12-chemistry-solid-state-29
ncert-exemplar-problems-class-12-chemistry-solid-state-30

Q 35.

Which of the following cannot be regarded as molecular solid?
(a) SiC (b) AIN
(c) Diamond (d) I2

Q 36.

In which of the following arrangements octahedral voids are formed?
(a) hep (b) bcc (c) simple cubic (d) fee

Q 37.

Frenkel defect is also known as
(a) stoichiometric defect (b) dislocation defect
(c) impurity defect (d) non-stoichiometric defect

Q 38.

Why are solids incompressible?

Q 39.

Why does table salt, NaCl sometimes appear yellow in colour?

Q 40.

Why does the electrical conductivity of semiconductors increase with rise in temperature?

Q 41.

Under which situations can an amorphous substance change to crystalline form?

Q 42.

How does the doping increase the conductivity of semiconductors?

Q 43.

What types of stoichiometric defects are shown by (C.B.S.E. Delhi 2013)
(i) ZnS
(ii) AgBr?

Q 44.

 Ionic solids, which have anionic vacancies due to metal excess defect, develop colour. Explain with the help of a suitable example.

Q 45.

A group 14 element is to be converted into n-type semiconductor by doping it with a suitable impurity. To which group should this impurity belong?

Q 46.

Ionic solids, which have anionic vacancies due to metal excess defect, develop colour. Explain with the help of a suitable example.

Q 47.

Niobium crystallises in a body centred cubic structure. If density is 8.55 g cm-3, calculate atomic radius of niobium, using its atomic mass 93u.

Q 48.

Analysis shows that nickel oxide has the formula Ni0.98 O1.00. What fractions of nickel exist as Ni2+ and Ni3+ ions?

Q 49.

In terms of band theory, what is the difference

  1. between a conductor and an insulator
  2. between a conductor and a semiconductor?

Q 50.

Classify .the following solids in different categories based on the nature of intermolecular forces operating in them: Potassium sulphate, tin, benzene, urea, ammonia, water, zinc sulphide, graphite, rubidium, argon, silicon carbide