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Question

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 B2O3<CO2<N2O3 acidic character Increase.
(ii) 3rd period Al2O3<SiO2<P4O10<SO3<Cl2O7 acidic character increases. On moving down the group, acidic character decreases and basic character increases e.g.,
(a)Natureofoxidesof13groupelementsB2O3Weakly acidicAl2O3Ga2O3AmphotericIn2O3BasicTI2OStrongly basic
(b) Nature of oxides of 15 group elements
N2O5StronglyacidicP4O10 ModeratelyAcidicAs4O10 AmphotericSb4O10 Amphoteric Bl2O3Basic
Among the oxides of same element, higher the oxidation state of the element, stronger is the acid, e.g., SO3 is a stronger acid than SO2
B2O3 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.
B2O3Boron trioxide+3H2O2H3BO3Orthoboric acidB(OH)3+HOH[B(OH)4]+H+

Al2O3 is amphoteric in nature, it is insoluble in water but dissolves in alkalies and reacts with acids.

Al2O3 + 2 NaOH 2 NaAlO2Sodium metaaluminate +H2O

Al2O3 + 6 HCl 2 AlCl3AlumniumChloride + 3 H2O

Tl2O is as basic as NaOH due to its lower oxidation state (+1)
Tl2O + 2HCl 2 TlCl + H2OP4O10 on reaction with water gives orthophosphoric acid
P4O10Phosphorous pentaoxide+6H2O4H3PO4OrthoPhospharic acid
Cl2O7 is strongly acidic in nature and on dissolution in water, it gives perchloric acid
2HClO4Dichlorine heptoxide+H2O2HClO4Perchloric acid


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