Which of the following is an Arrhenius acid?

Which of the following is an Arrhenius acid?

• A. NaOH
• B. NH3
• C. HCl
• D. Na2CO3

Answer: (C)

Arrhenius acids are substances that increase the hydrogen ion concentration in water by dissociating to release H+. In water, those H+ ions are effectively hydronium ions (H3O+). Among the options, the one that releases H+ when dissolved is the substance that acts as an Arrhenius acid: it dissociates to give H+ (and a counterion) in solution. The others do not increase H3O+—they either contribute OH− (as in a base) or involve ammonia acting as a base by accepting a proton from water to form NH4+ and OH−, or they form carbonate species that behave as bases in water. So the correct Arrhenius acid is the substance that directly increases hydronium ions in aqueous solution.

Arrhenius acids are substances that increase the hydrogen ion concentration in water by dissociating to release H+. In water, those H+ ions are effectively hydronium ions (H3O+). Among the options, the one that releases H+ when dissolved is the substance that acts as an Arrhenius acid: it dissociates to give H+ (and a counterion) in solution. The others do not increase H3O+—they either contribute OH− (as in a base) or involve ammonia acting as a base by accepting a proton from water to form NH4+ and OH−, or they form carbonate species that behave as bases in water. So the correct Arrhenius acid is the substance that directly increases hydronium ions in aqueous solution.