Which statement is true about weak acids?

Which statement is true about weak acids?

• A. They ionize completely in water
• B. They ionize in water but slowly
• C. They ionize only partially in water
• D. They do not ionize at all

Answer: (C)

In water, acid strength is about how much of the acid actually donates a proton at equilibrium. A weak acid only partially ionizes, so it establishes an equilibrium where most of the molecules remain undissociated and only a small portion split into H+ and A-. This partial ionization, reflected by a small acid dissociation constant (Ka), means the solution has a modest concentration of hydrogen ions and a relatively higher pH compared to strong acids of the same concentration. That’s different from strong acids, which ionize completely in water, producing lots of H+ and fully dissociated ions, making them strong electrolytes. Saying a weak acid ionizes slowly describes the rate of reaction rather than how much ionizes overall at equilibrium, so it doesn’t capture the defining trait. And saying it does not ionize at all isn’t correct for acids considered in this context.

In water, acid strength is about how much of the acid actually donates a proton at equilibrium. A weak acid only partially ionizes, so it establishes an equilibrium where most of the molecules remain undissociated and only a small portion split into H+ and A-. This partial ionization, reflected by a small acid dissociation constant (Ka), means the solution has a modest concentration of hydrogen ions and a relatively higher pH compared to strong acids of the same concentration.

That’s different from strong acids, which ionize completely in water, producing lots of H+ and fully dissociated ions, making them strong electrolytes. Saying a weak acid ionizes slowly describes the rate of reaction rather than how much ionizes overall at equilibrium, so it doesn’t capture the defining trait. And saying it does not ionize at all isn’t correct for acids considered in this context.