fibres and plastics

ASSIGNMENT: CLASS-XII
SUBJECT-CHEMISTRY
TOPIC- solid state
Potassium crystallizes in a body centred cubic lattice. Calculate the approximate number of unit cells in 1g of potassium. Atomic mass of potassium= 39u.
CsCl has bcc arrangement and its unit cell edge length is 400 pm. Calculate the interionic distance in CsCl. (D.S.B.E)
Cesium chloride forms a body centred cubic lattice. Cesium and chloride ions are in contact along the body diagonal of the cell. The length of the side of the unit cell is 412 pm and Cl- ion has a radius of 181 pm. Calculate the radius of Cs + ion.
The ions of NaF and MgO all have the same no. of electrons and the inter nuclear distances are about the same. Then why are their melting points so different?
Name the a) most symmetrical b) most unsymmetrical crystal system.
What is the maximum co-ordination number of an atom in a hcp crystal structure of an element? (D.S.B.E-2005)
How are unit cell and space lattice related?
Pick out the odd one from the following sets:
a) sulphur, argon, solid carbon dioxide, diamond.
b) SiC, quartz, BaO, graphite.
The radius of sodium ion and chloride ion is 95pm and 181pm resply. Predict whether the coordination no. of sodium ion is 6 or 4?
If the radius of bromide ion is 0.182 nm, how large a cation can fit in each of the tetrahedral hole?
A solid AB has rock salt structure. If the radius of cation A is 100 pm, what is the radius of anion B?
A compound formed by elements A & B crystallizes in the cubic arrangement, in which A atoms are at the corners of a cube and B atoms are at the face centers. What is the formula of the compound?
If three elements P, Q, R crystallize in a cubic solid lattice with P atoms at the corners, Q atoms at the cube center and R atoms at the edge centers, then write the formula of the compound.
When atoms are placed at the corners of all 12 edges of a cube, how many atoms are present per unit cell?
A unit cell consists of a cube in which there are anions(Y) at each corner and cations(X) at the center of alternate faces of the unit cell. What is the simplest formula of the compound? (C.B.S.E sample paper)
An ionic compound AB2 possesses CaF2 type crystal structure. Write the co-ordination no. Of the cation and anion in the crystal. ( D.S.B 2000)
Ferric oxide crystallizes in a hexagonal close packed array of oxide ions with two out of every three octahedral holes occupied by ferric ions. Derive the formula of the oxide.
A solid substance has rock salt geometry. What is the co-ordination no.of A & B? How many atoms of A& B are present in the unit cell?
In a solid, atoms A have ccp arrangement and atoms B occupy all the octahedral sites. If all the face centred atoms along one of the axes are removed, then what will be the resultant stoichiometry of the compound?
An element crystallizes in a structure having a fcc unit cell of an edge 200pm. Calculate its density if 200g of this element contain 24x1023 atoms.(A.I.S.B 1991)
An element has a body centred cubic structure with a cell edge of 288pm. The density of the element is 7.2g/cm3. how many atoms are present in 208g of the element? (D.S.B.E 2006)
An element crystallizes in fcc structure. 200g of this element has 4.12x1024 atoms. The density of this element is 7.2g/cm3. Calculate the edge length of the unit cell. (A.I.S.E 2001)
KF has rock salt structure. What is the distance between the ions in KF if density is 2.48g/cm3? (Haryana S.B. 2005)
Aluminium crystallizes in a cubic close packed structure. Its metallic radius is 125pm. What is the length of the side of unit cell and how many unit cells are there in 1.0 cm3 of aluminium? (D.S.B.E.2005, A.I.S.E.2005)
An element occurs in bcc structure with cell edge of 288pm. Its density is 7.2g/cm3. Calculate the atomic mass of the element. (Pb.S.B.E.2006)
What is the difference in the semiconductors obtained by doping silicon with As or Ga?
Non-stoichiometric cuprous oxide Cu2O can be prepared in the lab. 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?
Name a salt, which is added to AgCl so as to produce cation vacancies. (A.I.S.B.E.2003, D.S.B.E.2004)
Name the non-stoichiometric point defect responsible for colour in alkali metal halides. (A.I.S.B.E.2006)
Define dislocation in crystals.
Define coordination number.
Mention one property, which is caused by the presence of F-centres in a solid.
What makes alkali metal halides sometimes coloured, which are otherwise colourless? (D.S.B.2004)
Derive relationship between radius of a void( r) and radius of atom (R) in closed packed arrangement for a) octahedral void b) tetrahedral void.
Discuss the magnetic behaviour of transition metal oxides.
A compound AB has rock salt structure. The formula weight of the compound is 6.023y amu and the closest A---B distance is Y1/3 nm, where Y is an arbitrary constant.
a) Find the density of the lattice.
b) If the density of the lattice is found to be 20Kg/m3, predict the type of defect. (I.I.T.2004)
37. Sodium metal crystallizes in a body centred cubic lattice with cell edge, 4.29A0. What is the radius of sodium atom? (I.I.T.1994)
38. The composition of a sample of iron oxide is Fe0.93O1.00. What percentage of iron is present in the form of Fe(III)? (I.I.T.1997)
39. Chromium metal crystallizes in body centred cubic lattice. The length of the unit cell edge is 287pm. Calculate the atomic radius. What would be the density of chromium in g/cm3? Given, at. Mass of chromium is 51.996. (I.I.T.1997)

CLASS-XII
ASSIGNMENT: UNIT –1 (SOLID STATE)
Q1. A cubic solid is made up of two atoms A and B. Atoms A are present at the corners & B at the centre of the body. What is the formula of the unit cell?
Q2. Calculate the number of atoms in a cubic-based unit cell having one atom on each corner & two atoms on each body diagonal.
Q3. A unit cell consists of a cube in which there are A atoms at the corners & B atoms at the face centres. Two A atoms are missing from the two corners of the unit cell. What is the formula of the compound?
Q4. Name the non-stoichiometric point defect responsible for the colour in alkali metals.
Q5. In a cubic close packed structure of mixed oxides, it is found that lattice has O2- ions & one half of the octahedral voids are occupied by trivalent cations (A l3+) & one eighth of the tetrahedral voids are occupied by divalent cations (B2+). Derive the formula of the oxide.
Q6. How is pyroelectricity generated?
Q7. Aluminium metal forms a cubic face centred close packed structure. Its atomic radius is 125x10 -12m.
(a) Calculate the length of the side of the unit cell.
(b) How many unit cells are there in 1.0 m3 of aluminium
Q8. The edge length of NaCl unit cell is 564pm.What is the density of NaCl in g/cm3, if NaCl crystallizes in face centred cubic lattice.
Q9. An element crystallizes in astructure having a FCC unit cell of an edge 200pm. Calculate its density if 400 g of this element contain 48x1023 atoms.
Q10. An element A crystallizes in FCC structure. 200g of this element has 4.12x1024atoms. If the density of A is 7.2g/cm3 , calculate the edge length of the unit cell .
Q11. An element crystallizes in a BCC structure. The edge length of it’s unit cell is 288pm .If the density of the crystal is 7.3g/cm3, what is the atomic mass of the element?
Q12. Why is phosphorous doped silicon a semiconductor?
Q13. The density of chromium is 7.2g/cm3 .If the unit cell is a cubic with edge length of 289pm, determine the type of the unit cell. (atomic mass of Cr =52 u )
Q14.Frenkel defect is not found in the halides of alkali metals. Give reasons.
Q15. Schottky defect lowers the density of ionic crystals while Frenkel defect doesn’t. Discuss.
Q16. Why does ZnO that is white in colour become yellow on heating?
Q17. Why is latent heat of fusion of solid carbon dioxide less than that of SiO2 ?
Q18. The electrical conductivity of a metal decreases with rise in temperature while that of semiconductors increases. Justify.
ANSWERS
(1) AB (2) 9 (3) AB4 (5) A2BO4 (7) 2.25x1028 (8) 2.16g/cm3 (9) 41.67g/cm3 (10) 299.9 pm
(11) 52.51 g/mol (13) bcc .