Q24 of 26 Page 1

(a) Examine the given defective crystal:


Answer the following questions:


(i) Is the above defect stoichiometric or non-stoichiometric?


(ii) Write the term used for this type of defect. Give an example of the compound which shows this type of defect.


(iii) How does this defect affect the density of the crystal?


(b) Write two differences between amorphous solids and crystalline solids.


OR


(a) In terms of band theory, how are conductors different from semi conductors and insulators? Give one example of each.


(b) Why does the electrical conductivity of semi conductors increase with rise in temperature?


(c) What is the formula of a compound in which the element Y form hcp lattice and atom X occupies 1/3rd of octahedral voids?


(a) (i) The above defect is stoichiometric because the no. of missing cation and anion is equal. (A cation is missing from 2nd row and an anion is missing from 3rd row)


(ii) This defect is called Schottky defect. It is a vacancy defect shown by anionic substances in which cation and anion are of similar size.


An example of the compound which shows this type of defect is NaCl.


(iii) Since, the cations and anions are missing from the lattice thereby creating vacancy. Thus, density of crystal decreases.


(b)



OR


(a) In terms of band theory, conductors, semi conductors and insulators can be differentiated as follows-



(b) The electrical conductivity of semi conductors increase with rise in temperature because the energy gap between valence and conduction band in semi-conductor is very small and with rise in temperature, electrons can flow from valence band to conduction band thereby increasing conductivity.


(c) Since, Y forms hcp lattice, the no. of atoms of Y =


= 4


No. of tetrahedral voids in lattice = 2 (no. of atoms of Y)


= 2


Since, X occupy 1/3rd of tetrahedral voids, then no. of atoms of X = 8 =


Formula of compound =


= X2Y3


More from this chapter

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22

Define the following terms:

(i) Antacids (ii) Antiseptic (iii) Tranquillizers


 23

Sheela, domestic helper of Mrs. Vimla, fainted while sweeping the floor. Mrs. Vimla immediately took her to the nearby hospital where she was diagnosed to be severely anaemic. The doctor prescribed an iron rich diet and multi vitamins supplement to her. Mrs. Vimla supported her financially to get the medicines. After a month, Sheela was diagnosed to be normal.

After reading the above passage, answer the following questions.


(i) Name the vitamin whose deficiency causes pernicious anaemia.


(ii) What are vitamins and how are they classified?


(iii) What values (any two) are displayed by Mrs. Vimla?


 25

A translucent white waxy solid (A) on heating in an inert atmosphere is converted to its allotropic form (B). Allotrope (A) on reaction with aqueous KOH liberates highly poisonous gas (C) having rotten fish smell. With excess of chlorine forms (D), which on hydrolysis forms the compound (E). Identify the compounds A to E.

OR


Give reasons:


(i) H2S has a lower boiling point than H2O.


(ii) Reducing character decreases from SO2 to TeO2.


(iii) H2Te is the strongest reducing agent amongst all the hydrides of group 16 elements.


(iv) BiH3 is stronger reducing agent than SbH3.


(v) HF is not stored in glass bottles but is kept in wax coated glass bottles.


 26

An organic compound (A) on treatment with ethyl alcohol gives a carboxylic acid (B) and a compound (C). Hydrolysis of (C) under acidic conditions gives (B) and (D). (B) upon heating with Ca(OH)2 gives (E), C3H6O. Identify A, B, C, D and E.

OR


(a) How are the following obtained?


(i) Benzaldehyde from Benzoylchloride


(ii) Acetone from propan-2-ol


(b) Give chemical tests to distinguish between the following pairs of compounds.


(i) Pentan-2-one and Pentan-3-one


(ii) Benzaldehyde and Acetophenone


(c) Carboxylic acids do not give characteristic reactions of carbonyl group. Why?