Question

A metal A, which is used in the thermite process, when heated with oxygen gives an oxide B, which is amphoteric in nature. Identify A and B. Write down the reactions of oxide B with HCl and NaOH

Answer 1

Step 1: The metal A which is used in the Thermite process, when heated with Oxygen gives an Oxide B, which is amphoteric in nature:

• The metal A is Aluminium.
• When aluminum reacts with Oxygen, it forms an Aluminum oxide$\left({\mathrm{Al}}_2{\mathrm{O}}_3\right)$ which is an amphoteric oxide i.e. it behaves as both acidic as well as basic oxide.
• The chemical reaction can be depicted as:

$4\mathrm{Al}\left(\mathrm{s}\right)+3{\mathrm{O}}_2\left(\mathrm{g}\right)\to 2{\mathrm{Al}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)$

Step 2: The reaction of Aluminium oxide with Hydrochloric acid:

• When Aluminium oxide$\left({\mathrm{Al}}_2{\mathrm{O}}_3\right)$ reacts with Hydrochloric acid$\left(\mathrm{HCl}\right)$, it forms a salt of Aluminium which is Aluminium chloride$\left({\mathrm{AlCl}}_3\right)$ and water.
• The chemical reaction can be depicted as:

${\mathrm{Al}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)+6\mathrm{HCl}\left(\mathrm{aq}\right)\to 2{\mathrm{AlCl}}_3\left(\mathrm{s}\right)+3{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$

Step 3: The reaction of Aluminum oxide with Sodium hydroxide:

• When Aluminum oxide$\left({\mathrm{Al}}_2{\mathrm{O}}_3\right)$ reacts with Sodium hydroxide$\left(\mathrm{NaOH}\right)$, it forms Sodium aluminate$\left({\mathrm{NaAlO}}_2\right)$ and water.
• The chemical reaction can be depicted as:

${\mathrm{Al}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)+2\mathrm{NaOH}\left(\mathrm{aq}\right)\to 2{\mathrm{NaAlO}}_2\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$

Thus, A and B are Aluminum and Aluminium oxide respectively.