Question

Which of the following is the correct chemical formula of aluminium sulphate?
(A) \[A{{l}_{2}}S{{O}_{4}}\]
(B) \[A{{l}_{3}}{{(S{{O}_{4}})}_{2}}\]
(C) \[A{{l}_{3}}S{{O}_{4}}\]
(D) \[A{{l}_{2}}{{(S{{O}_{4}})}_{3}}\]

Answer 1

Hint: From the given question we can understand that the question is talking about aluminium metal and sulphate ion( which is a molecule or ion of sulphur and oxygen). Here we will balance oxIdation state of every atom or element.

Step by step solution:
* We know that a chemical formula shows the symbols of the elements in the compound and the ratio of the elements to one another. For example, the chemical formula for water is H₂O which indicates that 2 atoms of Hydrogen combine with 1 atom of oxygen. Or a chemical formula identifies each constituent element by its chemical symbol and indicates the proportionate number of atoms of each element.
* Aluminium sulfate is also called Filter Alum or Dialuminum trisulfate. It is a white crystalline solid in its anhydrous form and in its solution form it appears as a colourless liquid. Both the forms are non-toxic and noncombustible. Aluminium sulfate is formed by reacting with the correct amount of sulfuric acid to freshly precipitated aluminium hydroxide. 
* For the formula of aluminium sulphate we take aluminium and sulphate ions. Charge on sulphate ion is -2 (polyatomic ion) and charge or oxidation state of aluminium ion is +3(most common one). So by balancing the oxidation state formula of aluminium sulphate is: \[A{{l}_{2}}{{(S{{O}_{4}})}_{3}}\]
So, the correct option is “D”.

Note: Aluminium sulphate is used in baking soda, gardening to balance the soil pH, in the purification of water, the dyeing of cloth, making paper, printing on cloth, accelerator and waterproofing agent, firefighting foam, sewage treatment, fireproofing agent.