A solution is prepared by dissolving 0.025 mol of a strong diprotic acid H2A in water to make 500 mL of solution. What is the pH of the resulting solution? Assume complete dissociation.
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Correct answer
A. 1.00
Principle or equation
For a strong diprotic acid, each mole of H2A produces 2 moles of H+ ions. pH = -log[H+], where [H+] is the molar concentration of hydrogen ions.
Why this answer is correct
Calculate moles of H+: 0.025 mol H2A × 2 = 0.050 mol H+. Concentration [H+] = 0.050 mol / 0.500 L = 0.10 M. pH = -log(0.10) = 1.00.
Example
If 0.010 mol of H2SO4 is dissolved in 1.00 L, [H+] = 0.020 M, pH = 1.70.
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