Which of the following substances is an Arrhenius acid?

Which of the following substances is an Arrhenius acid?

• A. LiOH
• B. PO4-3
• C. CH3COOH
• D. CO3-2

Answer: (C)

Arrhenius acids are substances that increase the concentration of hydronium ions in water by donating a proton. Acetic acid, CH3COOH, does exactly that: it donates a proton to water to form CH3COO− and H3O+. This makes it an Arrhenius acid, even though it’s a weak one. LiOH, on the other hand, dissociates to give Li+ and OH−, raising hydroxide concentration rather than hydronium, so it behaves as an Arrhenius base. The phosphate ion (PO4^3−) and carbonate ion (CO3^2−) act as bases in water as well, accepting protons or generating OH− through hydrolysis, rather than donating H+. Therefore, the substance that fits the Arrhenius acid definition is acetic acid.

Arrhenius acids are substances that increase the concentration of hydronium ions in water by donating a proton. Acetic acid, CH3COOH, does exactly that: it donates a proton to water to form CH3COO− and H3O+. This makes it an Arrhenius acid, even though it’s a weak one.

LiOH, on the other hand, dissociates to give Li+ and OH−, raising hydroxide concentration rather than hydronium, so it behaves as an Arrhenius base. The phosphate ion (PO4^3−) and carbonate ion (CO3^2−) act as bases in water as well, accepting protons or generating OH− through hydrolysis, rather than donating H+. Therefore, the substance that fits the Arrhenius acid definition is acetic acid.