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GATE 2024 ES – Question 50

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

A buffer contains .1 M acetic acid and .05 M sodium acetate. Given pKa4.76,find pH, to two decimals.

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Correct answer: 4.46 to 4.46

Explanation

Use Henderson–Hasselbalch with conjugate-base/acid ratio: $pH=pK_a+\log_{10}([A^-]/[HA])=4.76+\log_{10}(.05/.10)=4.76-.30103=4.45897$. Rounded as requested,**4.46**. The ratio is below 1,so the pH is below pKa.

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