Statement 1: Heat evolved when 1 mole of H₃PO₄ is completely neutralized by excess NaOH is less than 3 × 57.1 kJ.
Statement 2: H₃PO₄ is a strong triprotic acid.

Question

Statement 1: Heat evolved when 1 mole of H 3 PO 4 is completely neutralized by excess NaOH is less than 3 × 57.1 kJ. Statement 2: H 3 PO 4 is a strong triprotic acid.

TestHub · Accepted Answer

H 3 PO 4 is a weak acid; part of the neutralization heat is consumed in ionizing its undissociated molecules, so the heat released per mole is less than 3 × 57.1 = 171.3 kJ even though three ionizable protons react (Statement 1 correct). It is precisely because H 3 PO 4 is weak, not strong, that this happens, so Statement 2 is incorrect. Ans: (c).

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