GATE 2016 CE (CE1) – Question 60

Water and Waste Water Quality and Treatment · Water quality standards, parameters and water quality index · 2 marks · Numerical answer

Effluent from an industry 'A' has a pH of 4.2. The effluent from another industry 'B' has double the hydroxyl (OH-) ion concentration than the effluent from industry 'A'. pH of effluent from the industry 'B' will be __________

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Correct answer: 4.4 to 4.6

Explanation

pOH=−log10[OH−], so doubling hydroxyl concentration lowers pOH by log10(2)=0.30103. At unchanged temperature pH+pOH is constant, hence pH rises by the same amount. Starting from4.2 gives **4.501**, approximately4.50. Doubling concentration does not double pH.