Question

Which of the following are Amphoteric oxides?
A. $Sn{{O}_{2}}$
B. $A{{l}_{2}}{{O}_{3}}$
C. $G{{a}_{2}}{{O}_{3}}$
D. $Si{{O}_{2}}$

Answer 1

Hint: Amphoteric oxides are those compounds which can react with both acids and base. Mostly Amphoteric oxides are formed by the metals. In periodic table elements to the leftmost corner form basic oxide, rightmost corner forms acidic oxide and elements in between forms Amphoteric oxide.

Complete step-by-step answer:As we know that amphoteric oxides react with both acids and base.
So, from the above given compounds $Sn{{O}_{2}}\,A{{l}_{2}}{{O}_{3}}\,G{{a}_{2}}{{O}_{3}}$are the amphoteric oxides.
This is because all these three can react with acids as well as a base, as discussed below:
a. $Sn{{O}_{2}}$reacts with the bases to form ‘’stannates’’and halogen acids attack $Sn{{O}_{2}}$to form hexahalostannates such as ${{\left[ Sn{{I}_{6}} \right]}^{2-}}$. Hence it is an amphoteric oxide.
b. $A{{l}_{2}}{{O}_{3}}$reacts with both acids and bases. The reactions are shown below;
$\begin{align}
  & A{{l}_{2}}{{O}_{3}}\,+\,6HCl\,\to \,2AlC{{l}_{3}}\,+\,3{{H}_{2}}O\, \\
 & A{{l}_{2}}{{O}_{3}}\,+\,2NaOH\,\to \,3{{H}_{2}}O\,+\,2NaAl{{\left( OH \right)}_{4}} \\
\end{align}$
Hence, we can say that Aluminum oxide $\left( A{{l}_{2}}{{O}_{3}} \right)$ is also an amphoteric oxide.
c. $G{{a}_{2}}{{O}_{3}}$also reacts with both acids and base and thus it is also an amphoteric oxide.
It reacts with base to form a solution of gallate ion $Ga{{\left( OH \right)}_{4}}^{-}$.
It reacts with hydrochloric acid as shown below
$G{{a}_{2}}{{O}_{3}}\,+\,6HCl\,\to 2GaC{{l}_{3}}\,+\,3{{H}_{2}}O$
d. Silicon dioxide $\left( Si{{O}_{2}} \right)$is an acidic oxide. It reacts with the strong bases to form silicate salts. Hence, it is not an amphoteric oxide.

Therefore, $A.\,S{{n}_{2}}{{O}_{3}}\,B.\,A{{l}_{2}}{{O}_{3}}\,C.\,G{{a}_{2}}{{O}_{3}}\,$are correct options.

Note:One can also generally identify amphoteric oxide as follows. If the oxide is formed from an element located at the left most corner, it is a basic oxide. If it is formed with an element at the right most corner, it forms acidic oxide. If it is formed by an element lying in between the periodic table, it is amphoteric oxide.