Question

The mass of aluminum in aluminum sulphate is $ 0.0675g $ . Find the mass of aluminium sulphate?

Answer 1

Hint: The aluminium sulphate is an ionic compound with molecular formula of $ A{l_2}{\left( {S{O_4}} \right)_3} $ . From the mass and molar mass of aluminium the moles will be determined. As the moles of aluminium are double to moles of sulphate, from then obtained moles of sulphate and molar mass of sulphate the mass of sulphate can be determined.

Complete Step By Step Answer:
Aluminium is a metal and can easily undergo loss of electrons or oxidation to form a positively charged ion known as cation. Sulphur and oxygen combine with each other and form an anionic group known as sulphate.
Aluminium sulphate is an ionic compound that was formed by the combination of aluminium ions whose molar mass is given as $ 27.0gmo{l^{ - 1}} $ and sulphate group. The molecular formula of $ A{l_2}{\left( {S{O_4}} \right)_3} $ whose molar mass is given as $ 342.15gmo{l^{ - 1}} $
The number of moles of aluminium in aluminium sulphate is $ \dfrac{{0.0675g}}{{27.0gmo{l^{ - 1}}}} = 0.0025mol $
From the dissociation of aluminium sulphate, it was clear that one mole of aluminium sulphate produces two moles of aluminium.
Thus, moles of aluminium sulphate is half of the moles of aluminium which will be $ \dfrac{{0.0025}}{2} = 0.00125mol $
Mass of aluminium sulphate is the product of moles and molar mass which will be $ 0.00125moles \times 342.15gmo{l^{ - 1}} = 0.428g $
Thus, the mass of aluminium sulphate is $ 0.428g $ .

Note:
Ionic compounds form by the combination of atoms or groups that have electronegativity difference and this compound can easily dissociate into ions. The number of aluminium ions produced from one mole of aluminium sulphate are two. Thus, the number of moles of aluminium sulphate is half of the number of moles of aluminium.