The GATE Grind

GATE 2022 CE (CE2) – Question 42

Water and Waste Water Quality and Treatment · Water quality standards, parameters and water quality index · 2 marks · Multiple choice

A 100 mg of HNO3 (strong acid) is added to water, bringing the final volume to 1.0 liter. Consider the atomic weights of H, N, and O, as 1 g/mol, 14 g/mol, and 16 g/mol, respectively. The final pH of this water is (Ignore the dissociation of water.)

  1. 2.8
  2. 6.5
  3. 3.8
  4. 8.5

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (A) 2.8

Explanation

HNO₃ has molar mass 63 g/mol and dissociates completely, supplying one hydrogen ion per molecule. Thus $[H^+]=0.100/63=0.00158730$ mol/L.

$pH=-\log_{10}[H^+]=2.79934$, or **2.8 (A)**. Convert milligrams to grams before dividing by molar mass.