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GATE 2024 ES – Question 54

Environmental Chemistry · Principles of Water Chemistry · 2 marks · Numerical answer

Mix2 MLD wastewater at 45°C, pH2 with 3 MLD at 30°C, pH8. Neglect buffering and temperature effects on pH. Find mixed pH, to two decimals.

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Correct answer: 2.38 to 2.41

Explanation

The acidic stream supplies approximately.01 M H⁺; the alkaline stream supplies10⁻⁶ M OH⁻ under the stipulated temperature-independent water-ion convention. Neutralize before volume averaging: $[H^+]\approx[2(.01)-3(10^{-6})]/5=.0039994$ M. Therefore $pH=-\log_{10}(.0039994)=2.3980$,rounded **2.40**. Arithmetic averaging of pH values is invalid because pH is logarithmic.

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