GATE 2021 ES – Question 41
A 200 mL sample atpH9 requires 25 mL of .02 N H₂SO₄ to reachpH4.5. Find total alkalinity in mg/L as NaHCO₃. Atomic masses Na23,H1,C12,O16,S32,Ca40.
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Correct answer: (C) 210
Explanation
Acid equivalents=.025(.02)=.0005 eq. Per litre sample, this is .0005/.200=.0025 eq/L. NaHCO₃ equivalent mass=84 g/eq, so alkalinity=.0025(84000)=**210 mg/L as NaHCO₃,C**. Normality already accounts for acid equivalents;do not multiply it by 2 again.