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UPSC Civil Service Exam Questions - Engineering

Q1:

A sample of ground water at a pH of 7.0 contains 122 mg/l of bicarbonates. What is the alkalinity of this water (in terms of CaC0 ) ?

A 120 mg/1

B 60 mg/1

C 100 mg/1

D 200 mg/l

ANS:C - 100 mg/1

Alkalinity, in this case, can be calculated as,
amount of sample in mg/L * (Equivalent wt of CaCo3/Equivalent wt of ion).

Here,
Amount of Sample = 122mg/L.
Equivalent wt of CaCO3 = 50.
Equivalent wt of HCO3-- = 61.

Therefore : 122*(50/61)=100mg/L as CaCO3.

Also,
Eq wt can be calculated as,
Eq Wt= Molecular Wt/Valancy.
Eq wt of CaCO3 = 100/2.
Wq wt of HCO3- = 61/1.
Molecular wt of HCO3-= (1+12+(16*3)) = 61.