In an aqueous solution, which substance yields hydrogen ions as the only positive ion?

In an aqueous solution, which substance yields hydrogen ions as the only positive ion?

• A. C2H5OH
• B. CH3COOH
• C. KH
• D. KOH

Answer: (B)

In water, acids increase the concentration of hydrogen ions by donating a proton to a water molecule, forming hydronium ions (H3O+). The positive ions present in solution come from this proton transfer, not from the conjugate base. Acetic acid does this: CH3COOH + H2O ⇌ H3O+ + CH3COO−. The only positive ion produced is hydronium, with acetate as the accompanying anion. Other substances behave differently: ethanol is essentially neutral in water, so it doesn’t produce H3O+ as a major ion; potassium hydride reacts with water to give K+ and OH− (not H3O+); potassium hydroxide dissociates to K+ and OH− as well. Thus, acetic acid is the one that yields hydrogen ions as the only positive ion.

In water, acids increase the concentration of hydrogen ions by donating a proton to a water molecule, forming hydronium ions (H3O+). The positive ions present in solution come from this proton transfer, not from the conjugate base.

Acetic acid does this: CH3COOH + H2O ⇌ H3O+ + CH3COO−. The only positive ion produced is hydronium, with acetate as the accompanying anion. Other substances behave differently: ethanol is essentially neutral in water, so it doesn’t produce H3O+ as a major ion; potassium hydride reacts with water to give K+ and OH− (not H3O+); potassium hydroxide dissociates to K+ and OH− as well. Thus, acetic acid is the one that yields hydrogen ions as the only positive ion.