Question

Alums purify muddy water by:
A.Dialysis
B.Absorption
C.Coagulation
D.Forming true solution

Answer 1

Hint: Aluminium sulfate is widely known as Alum. So, when alum is added to raw water it reacts with the bicarbonate alkalinities present in the water and forms gelatinous precipitate. Moreover, alum in its crystalline form can be stored in a clean glass container.

Complete step by step answer:
So basically, aluminium sulfate is also known as Filter alum or Dialuminium trisulfate. It is generally a white crystalline solid in its anhydrous form and is a colorless liquid in its solution form. Both the forms are non-toxic and non-combustible. Moreover, it is formed by reacting the correct amount of sulfuric acid with freshly precipitated aluminium hydroxide. After that, the resulting solution is evaporated and allowed to crystallize and we obtain pure, lustrous crystals, granules or powder.
Now, alums purify muddy water by coagulation. Basically, coagulation involves the addition of compounds to obtain pure substances or to separate certain compounds. Now, the $A{l^{3 + }}$ ion has high coagulating power so it will easily coagulate the negative solution. Now, muddy water is a negative solution, so $A{l^{3 + }}$ will coagulate the impurities in muddy water and hence due to coagulation the impurities will settle down and we will obtain a pure solution. Moreover, when alum is added to raw water, it reacts with the alkalinities present in water and forms a gelatinous precipitate. Further, this flock attracts the other fine particles in raw material. As a result, the water obtained over this sediment is almost clean.

Hence, option C is correct.

Note:Aluminium sulfate has various applications. It is used in baking soda, in purification of water, in making paper, in dyeing of cloth, in sewage treatment etc. Moreover, it causes irritation to skin and eyes so it should be handled with care. It is mildly dangerous if swallowed because it can form extremely corrosive sulfuric acid.