p - block elements form acidic, basic and amphoteric oxides. Explain each property by giving two examples and also write the reactions of these oxides with water.

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Solution

In p - block, when we move from left to right in a period, te acidio character of the oxides increases due to increase in electronegativity. e.g,
(i) 2nd period $B_{2} O_{3} < C O_{2} < N_{2} O_{3}$ acidic character Increase.
(ii) 3rd period $A l_{2} O_{3} < S i O_{2} < P_{4} O_{10} < S O_{3} < C l_{2} O_{7}$ acidic character increases. On moving down the group, acidic character decreases and basic character increases e.g.,
$(a) N a t u r e o f o x i d e s o f 13 g r o u p e l e m e n t s B_{2} O_{3} W e a k l y a c i d i c A l_{2} O_{3} G a_{2} O_{3}      A m p h o t e r i c I n_{2} O_{3} B a s i c T I_{2} O S t r o n g l y b a s i c$
(b) Nature of oxides of 15 group elements
$N_{2} O_{5} \begin{matrix} S t r o n g l y a c i d i c \end{matrix} P_{4} O_{10} \begin{matrix} M o d e r a t e l y A c i d i c \end{matrix} A s_{4} O_{10} A m p h o t e r i c S b_{4} O_{10} A m p h o t e r i c B l_{2} O_{3} B a s i c$
Among the oxides of same element, higher the oxidation state of the element, stronger is the acid, e.g., $S O_{3}$ is a stronger acid than $S O_{2}$
$B_{2} O_{3}$ is weakly acidic and on dissolution in water, it forms orthoboric acid Orthoboric acid does not act as a protonic acid(It does not ionise) but acts as a weak Lewis aoid.
$B_{2} O_{3} B o r o n t r i o x i d e + 3 H_{2} O ⇌ 2 H_{3} B O_{3} O r t h o b o r i c a c i d B (O H)_{3} + H - O H \Rightarrow [B (O H)_{4}]^{-} + H^{+}$

$A l_{2} O_{3}$ is amphoteric in nature, it is insoluble in water but dissolves in alkalies and reacts with acids.

$A l_{2} O_{3} + 2 N a O H △ - \to 2 N a A l O_{2} S o d i u m m e t a a l u m i n a t e + H_{2} O$

$A l_{2} O_{3} + 6 H C l △ - \to 2 A l C l_{3} A l u m n i u m C h l o r i d e + 3 H_{2} O$

$T l_{2} O$ is as basic as NaOH due to its lower oxidation state (+1)
$T l_{2} O + 2 H C l \to 2 T l C l + H_{2} O P_{4} O_{10} o n r e a c t i o n w i t h w a t e r g i v e s o r t h o p h o s p h o r i c a c i d$
$P_{4} O_{10} P h o s p h o r o u s p e n t a o x i d e + 6 H_{2} O ⟶ 4 H_{3} P O_{4} O r t h o - P h o s p h a r i c a c i d$
$C l_{2} O_{7}$ is strongly acidic in nature and on dissolution in water, it gives perchloric acid
$2 H C l O_{4} D i c h l o r i n e h e p t o x i d e + H_{2} O ⟶ 2 H C l O_{4} P e r c h l o r i c a c i d$

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