Which of the following is the correct method to calculate the percent ionization of HA in a 0.10 M solution, given that the acid dissociation constant (K_a) is known?

• A. Percent ionization = ( K_a / [HA] ) × 100
• B. Percent ionization = ( [HA] / [H^+] ) × 100
• C. Percent ionization = ( [A^-] / K_a ) × 100
• D. Percent ionization = ( [H^+] / 0.10 ) × 100

Answer: (D)

Verified step by step guidance

1. Understand that percent ionization refers to the fraction of the original acid (HA) that dissociates into ions in solution, expressed as a percentage.
2. Recognize that in the dissociation of a weak acid HA, the concentration of hydrogen ions [H^+] produced is equal to the concentration of the conjugate base [A^-] formed.
3. Recall that percent ionization is calculated by dividing the concentration of ionized acid (which is [H^+]) by the initial concentration of the acid ([HA]_initial), then multiplying by 100 to convert to a percentage.
4. Express the formula for percent ionization as: \(\text{Percent ionization} = \left( \frac{[H^+]}{[HA]_{initial}} \right) \times 100\)
5. Note that the acid dissociation constant \(K_a\) is used to find the equilibrium concentration of \([H^+]\), but the percent ionization itself depends on the ratio of \([H^+]\) to the initial acid concentration, not directly on \(K_a\).