Q. 25

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Answer :

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 (SO2SO3) 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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