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Why is 0.15 M of hypochlorous acid acidic and 0.15 M of sodium hypochlorite basic?

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Answer:

HOCl is such a weak acid that the basicity of the OCl⁻ predominates in the mixture.

Explanation:

HOCl is a weak acid with pKₐ 7.53. NaOCl is its salt. A solution of a weak acid and its salt is a buffer. We can calculate the pH of the buffer.

Step 1. Write the equation for the equilibrium

HOCl + H₂O ⇌ H₃O⁺ + OCl⁻; pKa = 7.53

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Step 2. Calculate the pH of the buffer

The Henderson-Hasselbalch equation is

pH = pKₐ + log([OCl⁻]/[HOCl])

pH = 7.53 + log(0.15/0.15)

pH = 7.53 + log1

pH= 7.53 + 0

pH = 7.53

So, the solution is basic.

The conjugate base of a weak acid is a relatively strong base.

HOCl is such a weak acid that the basicity of its conjugate base predominates in an equimolar mixture of the two components.

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