Question

Aluminium reacts with sulphuric acid to form aluminium sulphate. Write the molecular formula of aluminium sulphate.

Answer 1

Hint: Aluminium is a metal with the symbol $Al$. It has a silvery white appearance. Metals react with acids to liberate hydrogen gas. Similarly aluminium also reacts with sulphuric acid to liberate hydrogen gas.

Complete step by step answer:
We know aluminium is a metal and metals react with acid to liberate hydrogen gas. In this question metal is aluminium and acid is sulphuric acid. We have to find a formula of aluminium sulphate which is also formed as a product along with hydrogen gas. Chemical formula of aluminium is $Al$ and sulphuric acid is ${H_2}S{O_4}$ . The reaction that will take place is:
$2Al + 3{H_2}S{O_4}\xrightarrow[{}]{}A{l_2}{\left( {S{O_4}} \right)_3} + 3{H_2}$
In above reaction $Al$ is aluminium, ${H_2}S{O_4}$ is sulphuric acid, ${H_2}$ is hydrogen gas and $A{l_2}{\left( {S{O_4}} \right)_3}$ is aluminium sulphate.
Charge on aluminium ion is $ + 3$, this means it is cation and charge on sulphate ion is $ - 2$, this means it is anion. To make a compound neutral which is composed of aluminium and sulphate ion we have to take two ions of aluminium so that total positive charge will be $3 \times 2 = 6$ and three ions of sulphate so that total negative charge is $2 \times 3 = 6$. Now, cationic charge is equal to anionic charge; this means compound is neutral.
So, formula of aluminium sulphate is $A{l_2}{\left( {S{O_4}} \right)_3}$
Additional information: In this reaction hydrogen gas is liberated. This gas is highly explosive. To test the presence of hydrogen gas during a reaction (on a small scale) a burning matchstick is brought near the face of the test tube. A pop sound will be produced if hydrogen gas is liberated (as it burns). But on large scale it is not preferable as hydrogen is highly flammable gas due to which an explosion may take place.
Note:
Aluminium oxide is amphoteric in nature this means it reacts with both acids and bases. Along with aluminium, copper, zinc, tin, lead is also amphoteric in nature. Oxides and hydroxides of these metals react with both acids and bases.