Which substance can act as an Arrhenius acid in aqueous solution?

Which substance can act as an Arrhenius acid in aqueous solution?

• A. NaI
• B. LiH
• C. NH3
• D. HI

Answer: (D)

Arrhenius acids are substances that increase the concentration of hydronium ions (H3O+) in water. Hydroiodic acid does exactly this: it dissociates in aqueous solution to give H3O+ and I−, so the solution becomes acidic. Other substances listed do not raise H3O+ in water. A salt like sodium iodide simply splits into Na+ and I−; it doesn’t contribute hydronium ions. A hydride such as lithium hydride reacts with water to form lithium hydroxide and hydrogen gas, which makes the solution basic, not acidic. Ammonia in water acts as a base, accepting a proton to produce ammonium and OH−, again not increasing H3O+. So the substance that can act as an Arrhenius acid in aqueous solution is hydroiodic acid, HI.

Arrhenius acids are substances that increase the concentration of hydronium ions (H3O+) in water. Hydroiodic acid does exactly this: it dissociates in aqueous solution to give H3O+ and I−, so the solution becomes acidic.

Other substances listed do not raise H3O+ in water. A salt like sodium iodide simply splits into Na+ and I−; it doesn’t contribute hydronium ions. A hydride such as lithium hydride reacts with water to form lithium hydroxide and hydrogen gas, which makes the solution basic, not acidic. Ammonia in water acts as a base, accepting a proton to produce ammonium and OH−, again not increasing H3O+.

So the substance that can act as an Arrhenius acid in aqueous solution is hydroiodic acid, HI.