10.5 Nitrogen pentaoxide $N_2O_5$

  p Block Elements

This oxide is also known as nitric anhydride.

Preparation:

It is prepared by distilling concentrated nitric acid with phosphorous pentoxide in glass apparatus.$${P_2}{O_5} + 2HN{O_3} \to 2HP{O_3} + {N_2}{O_5}$$

It is also prepared by the action of dry chlorine on silver nitrate at $95^\circ C$

$$4AgN{O_3} + 2C{l_2} \to 4AgCl + 2{N_2}{O_5} + {O_2}$$

Properties:

(a) It is white crystalline solid. The crystals melt at 30 C giving a yellow liquid which decomposes at 40 C to give brown $N_2O$. The decomposition occurs with the explosion.$$2{N_2}{O_5} \to 4N{O_2} + {O_2}$$

(b) It is an acidic oxide, It is with water with hissing sound forming nitric acid.$${N_2}{O_5} + {H_2}O \to 2HN{O_3}$$on account of this, it is known as nitric anhydride, with alkalies if forms nitrates.$$2NaOH + {N_2}{O_5} \to 2NaN{O_3} + {H_2}O$$

(c) It acts as strong oxidizing agent. It affects organic substances such as cork, rubber, etc. It oxidizes iodine readily into iodine pentaoxide.$${I_2} + 5{N_2}{O_5} \to {I_2}{O_5} + 10N{O_2}$$

(d) With aqueous $Nacl$, the ionic reaction takes place.$${N_2}{O_5} + NaCl \to NaN{O_3} + N{O_2}Cl$$

The reaction proves that $N_2O_5$ exists as ionic nitronium nitrate$(NO_2,NO_3)$

(e) $N_2O_5$ is decomposed by alkali metals.

Structure:

In the gaseous state, it exists as a symmetrical molecule having structure $O_2N-O-NO_2,N-O-N$ bond is almost linear. It may be represented as:

X-ray studies suggest that solid $N_2O_5$ is ionic in nature, i,e, nitronium nitrate, $NO_2,NO_3$.