Unit 2 Practice Questions (Q14) - Environmental Sciences

ICAR JRF Environmental Sciences 29 Jun 2024Shift 1

MCQ (Single Correct) +4 −1

Which of the following gas is released when alum is added to water?

Ca (OH)3 C02 Correct Al (OH)3 CaSOx

Alum Coagulation Chemistry:
When filter alum (aluminum sulfate, $Al_2(SO_4)_3 \cdot 18H_2O$) is dosed into raw water containing natural calcium bicarbonate alkalinity:

$$Al_2(SO_4)_3 + 3Ca(HCO_3)_2 \rightarrow 2Al(OH)_3\downarrow + 3CaSO_4 + 6CO_2\uparrow$$

Insoluble aluminum hydroxide floc precipitates out, while gaseous carbon dioxide ($CO_2$) is liberated into solution, slightly lowering water pH. (Correct answer: Option 2)

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