Chemistry

The Solid State

Question:

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?

Answer:

No. of atoms in close packings 0.5 mol =0.5 x 6.022 x  1023  =3.011 x  1023
No. of octahedral voids = No. of atoms in packing =3.011 x  1023
No. of tetrahedral voids = 2 x No. of atoms in packing
= 2 x 3.011 x 1023  = 6.022 x 1023
Total no. of voids = 3.011 x 1023  + 6.022 x 1023
= 9.033 x 1023

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The Solid State

Q 1.

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

Q 2.

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

Q 3.

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

Q 4.

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

Q 5.

Under the influence of electric field, which of the following statements are true about the movement of electrons and holes in a p-type semiconductor?
(a) Electron will move towards the positively charged plate through electron holes
(b) Holes will appear to be moving towards the negatively charged plate
(c) Both electrons and holes appear to move towards the positively charged plate
(d) Movement of electrons is not related to the movement of holes

Q 6.

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

Q 7.

How does the doping increase the conductivity of semiconductors?

Q 8.

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

Q 9.

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

Q 10.

Why are solids rigid?

Q 11.

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?

Q 12.

Give the significance of a ˜lattice point'.

Q 13.

Distinguish between
(i) Hexagonal and monoclinic unit cells
(ii) Face-centred and end-centred unit cells.

Q 14.

(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 15.

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 16.

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

Q 17.

 Distinguish between :
(i) Hexagonal and monoclinic unit cells
(ii) Face-centred and end-centred unit cells.

Q 18.

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 19.

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?

Q 20.

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

Q 21.

In which pair most efficient packing is present?
(a) hep and bcc (b) hep and ccp
(c) bcc and ccp (d) bcc and simple cubic cell

Q 22.

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

Q 23.

In spite of long range order in the arrangement of particles why are the crystals usually not perfect?

Q 24.

What is the two-dimensional coordination number of a molecule in a square close-packed layer?

Q 25.

 (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 26.

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 27.

Aluminium crystallises in a cubic close packed structure. Its metallic radius is 125 pm.

  1. What is the length of the side of the unit cell?
  2. How many unit cells are there in 1.00 cm3 of aluminium?

Q 28.

Why do solids have a definite volume?

Q 29.

What is the two-dimensional coordination number of a molecule in square close-packed layer?

Q 30.

What type of stoichiometric defect is shown by:
(i)ZnS (ii)AgBr

Q 31.

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 32.

 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 33.

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

Q 34.

Ferric oxide crystallises in a hexagonal dose- packed array of oxide ions with two out of every three octahedral holes occupied by ferric ions. Derive the formula of the ferric oxide.

Q 35.

In terms of band theory, what is the difference

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

Q 36.

Explain the following with suitable example:

  1. Ferromagnetism
  2. Paramagnetism
  3. Ferrimagnetism
  4. Antiferromagnetism
  5. 12-16 and 13-15 group compounds.

Q 37.

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

Q 38.

Explain how much portion of an atom located at
(i)corner and (ii)body centre of a cubic unit cell is part of its neighbouring unit cell.

Q 39.

What makes a glass different from a solid such as quartz? Under what conditions could quartz be converted into glass?

Q 40.

Which of the following features are not shown by quartz glass?
(a) This is a crystalline solid
(b) Refractive index is same in all the directions
(c) This has definite heat of fusion
(d) This is also called super cooled liquid

Q 41.

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

Q 42.

Assertion (A): Semiconductors are solids with conductivities in the intermediate range from
ncert-exemplar-problems-class-12-chemistry-solid-state-51
Reason (R): Intermediate, conductivity in semiconductor is due to partially filled valence band.

Q 43.

How can you determine the atomic mass of an unknown metal if you know its density and the dimensions of its unit cell? Explain.

Q 44.

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 45.

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 46.

Classify the following as amorphous or crystalline solids: Polyurethane, naphthalene, benzoic acid, Teflon, potassium nitrate, cellophane, polyvinyl chloride, fibreglass, copper

Q 47.

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 48.

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 49.

Iodine molecules are held in the crystals lattice by
(a) London forces (b) dipole-dipole interactions
(c) covalent bonds (d) coulombic forces

Q 50.

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