Q25 of 26 Page 1

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.


A = white phosphorus (translucent white waxy solid)


B = red phosphorus (obtained by heating white phosphorus at 573 K in an inert atmosphere)


C = Phosphine, PH3 (rotten fish smell and highly poisonous gas)


P4 +3KOH +3H2O PH3 + 3KH2PO2


D = Phosphorus pentachloride, PCl5


P4 + 10 Cl2 4PCl5


E = Phosphorus acid, H3PO4


PCl5 + 4 H2O 5HCl + H3PO4


OR


(i) H2S has a lower boiling point than H2O. As O has a smaller size and higher electronegativity than S, H2O molecules are associated through strong intermolecular H-bonding. Hence, it boils at a higher temperature than H2S in which no such bonding exists.


(ii) SO2 is a strong reducing agent which means it will get oxidized (SO2→SO3) and oxidation state of sulphur will change from +4 to +6 and in case of sulphur +6 is more stable than +4. So it will quickly oxidize to a more stable state reducing others. Whereas in case of TeO2, Te is more stable in +2 oxidation state than +4 so it will reduce quickly to lower stable state oxidizing others. Thus, reducing character decreases from SO2 to TeO2.


(iii) H2Te is the strongest reducing agent amongst all the hydrides of group 16 elements because the bond dissociation enthalpy of hydrides decreases down the group due to increase in size of group 16 elements and thus, reducing character increases.


(iv) BiH3 is stronger reducing agent than SbH3 because the bond dissociation enthalpy of hydrides decreases down the group due to increase in size of group 15 elements and thus, reducing character increases.


(v) HF is not stored in glass bottles but is kept in wax coated glass bottles because HF reacts with glass. It reacts with SiO2 to form [SiF6]2- ions which are quite stable. Hence, in order to store HF we use wax coated glass bottles.


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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?


 24

(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?


 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?