Solid State Exercise - II

SOLID STATE EXERCISE – II BOARD PROBLEMS Q.1 Name a substance which on addition to AgCl causes cation vacancy in it. Q.2 Calculate the density of silver which crystallises in the fcc structure. The distance between the nearest silver atoms in this structure is 287 pm. (Molar mass of Ag = 107.87 g/mol) Q.3 What makes alkali metal halids sometimes coloured, which are otherwise colourless? Q.4 Define the term amorphous. Q.5 Calculate the value of Avogadro's constant from the following data: Density of NaCl = 2.165 g/cm3 Distance between Na+ and Cl– in NaCl = 281 pm (Molar mass of NaCl = 58.5 g/mol) Q.6 Which point defect lowers the density of a crystal? Q.7 What is meant by coordination number in an ionic crystal? Q.8 What is the maximum possible coordination number of an atom in an hcp crystal structure of an element ? Q.9 Aluminium metal forms a cubic close packed crystal structure. Its atomic radius is 125 × 10–12 m (a) calculate the length of the side of the unit cell. (b) How many such unit cells are there in 1.00 m3 of aluminium? A cubic solid is made of two elements X and Y. Atoms Y are at the corners of the cube and X at the body centre. What is the formula of the compound? Q.10 Q.11 An element has a body-centred cubic ctructure with a cell edge of 288 pm. The density of the element is 7.2 g/cm3. Calculate the number of atoms present in 208 g of the element. Q.12 Name the non-stoichiometric point defect responsible for colour in alkyl halides. Q.13 Calculate the distance between Na+ and Cl– ions in NaCl crystal if its density is 2.165 g/cm3. [Molar mass of NaCl = 58.5 g/mol] Q.14 Assign reasons for the following : (i) Phosphorus doped silicon is a semiconductor. (ii) Schollky defect lowers the density of a solid. (iii) Some of very old glass objects appear slightly milky instead of being transparent. Q.15 What is the number of atoms per unit cell in a body -centred cubic structure? Q.16 What is a semiconductor? Describe the two main types of semiconductors and explain mechanism of their conduction. SOLID STATE Q.17 What is the total number of atoms per unit cell in a face centred cubic structure? Q.18 How do you account for the following? (i) Frenkel defects are not found in alkali metal halides. (ii) Schottky defects lower the density of related solids. (iii) Impurity doped silicon is a semiconductor. Q.19 Explain the following properties giving suitable examples (i) Ferromagnetism (ii) Paramagnetism (iii) Ferrimagnetism Q.20 Silver crystallises in a fcc lattice. The edge length of its unit cell is 4.077 × 10–8 cm and its density is 10.5 g cm–3. Calculate on this basis the atomic mass of silver. Q.21 What are F-centres ? Q.22 Account for the following: (i) Fe3O4 is ferrimagnetic at room temperature but becomes paramagnetic at 850 K. (ii) Zinc oxide on heating becomes yellow. (iii) Frenkel defect does not change the density of AgCl crystals. Q.23 With the help of suitable diagrams on the basis of bond theory explain the difference between. (i) A conductor and an insulator. (ii) A conductor and a semiconductor. Q.24 Why is glass considered a supercooled liquid? Q.25 The density of copper metal is 8.95 g cm–3. If the radius of copper atom be 137.8 pm, is the copper unit cell simple cubic, body/centred cubic or face-centred cubic? Q.26 What is the number of atoms in a unit cell of a face- centred cubic crystal ? Q.27 Silver crystalises with face-centred cubic unit cells. Each side of the unit cell has a length of 409 pm. What is the radius of an atom of silver? (Assume that each face atom is touching the four corner atoms.) Q.28 Calculate the packing efficiency of a metal crystal for a simple cubic lattice. Q.29 Explain how you can determine the atomic mass of an unknown metal if you know its mass density and the dimensions of unit cell of its crystal. Q.30 What are n-type semiconductors ? Q.31 Copper crystallises with face centred cubic unit cell. If the radius of copper atom is 127.8 pm, calculate the density of copper metal. (Atomic mass of Cu = 63.55 u and Avogadro's number NA = 6.02 × 1023 mol–1) OR Iron has a body centred cubic unit cell with the cell dimension of 286.65 pm. Density of iron is 7.87 g cm–3. Use this information to calculate Avogadro's number. (Atomic mass of Fe = 56.0 u) Q.32 The density of copper metal is 8.95 g cm–3. If the radius of copper atom be 127.8 pm, is the copper unit cell simple cubic, body centred cubic or face-centred cubic ? (given : atomic mass of Cu = 63.54 g mol–1 and NA = 6.02 × 1023 mol–1) Q.33 (a) What change occurs when AgCl is doped with CdCl2 ? (b) What type of semiconductor is produced when silicon is doped with boron ? Q.34 Aluminium crystallizes in an fcc structure. Atomic radius of the metal is 125 pm. What is the length of the side of the unit cell of the metal ?