Define : Cryoscopic constant
What is the action of hot/concentrated nitric acid on :
(a) Arsenic
(b) Antimony
Draw the structure of :
(a) Orthophosphoric acid
(b) Pyrophosphoric acid

Explanation

Cryscopic constant or molal depression constant is the depression in frrzing point produced by dissolving 1 mole of solute in 1 kg of solvent . Its units are K kg ` "mol"^(-1) or .^(@)C "kg mol"^(-1)` or K/molal .
(a) When the concentrated nitric acid reacts with the arsenic it forms arsenic acid .
` {:(5 HNO_(3),+,As,rarr,H_(3)AsO_(4),+,5NO_(2),H_(2)O),(("conc."),,,,("Arsenic acid"),,,):}`
(b) When the hot or concentrated nitric acid react with the antimony it forms a compound named as antimony pentoxide .
` {:(4Sb,+,20HNO_(3),to,Sb_(4)O_(10),+,20NO_(2),+,10H_(2)O),(,,("conc."),,("Antimony oxide"),,,,):}`
( a) Orthophosphoric Acid `(H_(3)PO_(4))` :

( b) Pyrophosphoric Acid `(H_(4)P_(2)O_(7)`) :
`HO-overset(OH)overset("| ")underset("O ")underset("|| ")("P ")-O-overset(OH)overset("| ")underset("O ")underset("|| ")("P ")-OH`