Question

What is the colour of the solution of $Al_2(SO_4)_3$ , in water?
A.Blue
B.Pink
C.Colourless
D.Green

Answer 1

Hint: Aluminium sulphate, also known as $Al_2(SO_4)_3$, is a chemical compound that has the formula $Al_2(SO_4)_3$. It is soluble in water and is mostly used as a coagulating agent (a neutralising charge that promotes particle collision) in the purification of drinking water and wastewater treatment plants, as well as in the production of paper.

Complete answer: Aluminium sulphate is used to purify water and as a mordant in cloth dyeing and printing. It allows suspended impurities in water to coagulate into larger particles, which can then quickly settle to the bottom of the bottle (or be flushed out). Coagulation or flocculation is the term for this process. According to research, the main cause of hydrogen sulphide gas in sanitary sewage systems in Australia is aluminium sulphate used in this manner in drinking water treatment.
Aluminium sulphate creates a gelatinous precipitate of aluminium hydroxide, Al(OH)₃, when immersed in a large volume of neutral or mildly alkaline water. The gelatinous precipitate aids dye adhesion to clothing fabrics by making the ink insoluble when dyeing and printing fabric.
As aluminium sulphate reacts with water, it produces aluminium hydroxide and sulphuric acid. Aluminium sulphate is white in colour and becomes colourless when hydrolyzed. The reaction takes place in a molten aluminium sulphate solution. It is mostly used as a coagulant.
\[A{l_2}S{O_4} + {H_2}O \to Al{(OH)_3} + {H_2}S{O_4}\]
Hence, it is White in colour.

Note:
Aluminum sulphate allows small impurities to clump together into larger and larger fragments when exposed to water. These clumps then sink to the bottom of the bottle, where they can be flushed out. As a result, the water is better to drink.