Question

$A{{l}_{2}}{{\left( S{{O}_{4}} \right)}_{3}}$ is used in the following but not:
A) As a coagulant in treating drinking water and sewage
B) In plastic industry
C) As a mordant in dyeing
D) In paper industry
E) Both as a mordant in dyeing and in paper industry

Answer 1

It is a factual type of question about the uses of the compound $A{{l}_{2}}{{\left( S{{O}_{4}} \right)}_{3}}$
The $A{{l}_{2}}{{\left( S{{O}_{4}} \right)}_{3}}$ is generally referred to as filter alum.

Complete Solution :
So this is a factual question,in which the options given are the fields where $A{{l}_{2}}{{\left( S{{O}_{4}} \right)}_{3}}$ may find application, we have to sort it according to the role $A{{l}_{2}}{{\left( S{{O}_{4}} \right)}_{3}}$ in different industries and its uses and find the odd one out ie we have to correctly find the industry where $A{{l}_{2}}{{\left( S{{O}_{4}} \right)}_{3}}$is not used.
- This is an easy question, if we know the uses of the aluminium sulphate compound we could easily sort it.
- Before going into the solution lets discuss some facts –general properties and uses about the compound $A{{l}_{2}}{{\left( S{{O}_{4}} \right)}_{3}}$,which would serve as an bonus tip, if some factual type question on $A{{l}_{2}}{{\left( S{{O}_{4}} \right)}_{3}}$ may be asked.
- So $A{{l}_{2}}{{\left( S{{O}_{4}} \right)}_{3}}$ is a sulphate compound of Al. It possesses a white crystalline solid state in its anhydrous form i.e when not associated with water of crystallisation. But when dissolved it forms a colourless solution. It is non-toxic in both forms but its decomposition product which is umes of sulphate is highly toxic.
- It is an odourless compound and possesses sweet taste or similar to astringent.
- It is generally by adding sulphuric acid to calcium hydroxide and this mixture on reaction finally yields the aluminium sulphate.

Uses- The $A{{l}_{2}}{{\left( S{{O}_{4}} \right)}_{3}}$ possess the coagulating property ie it separates out the suspension or colloids from the solution and it is used as a coagulant in removing sewage waste, in the process of purification of water, in paper industry etc.
- It also finds application as a mordant in the textile industry where these mordants are used during dyeing.
- Hence from the above options given the $A{{l}_{2}}{{\left( S{{O}_{4}} \right)}_{3}}$ is not used in plastic industry.
So, the correct answer is “Option B”.

Note: Many refer $A{{l}_{2}}{{\left( S{{O}_{4}} \right)}_{3}}$ as alum, since alum is also a sulphate of aluminium but alum is disulphate of aluminum with general formula $XAl{{(S{{O}_{4}})}_{2}}.12{{H}_{2}}O$, where X is any monovalent atom. We generally refer to alum as Potassium Aluminium sulphate.