Question

which of the following substances is an arrhenius acid?
○ bf₃
○ hcn
○ nh₃
○ mg(oh)₂

Explanation:

An Arrhenius acid is a substance that dissociates in water to produce hydrogen ions ($\ce{H+}$).

• $\ce{BF3}$ is a Lewis acid (accepts electron pairs) and does not produce $\ce{H+}$ in water.
• $\ce{HCN}$ (hydrocyanic acid) dissociates in water as $\ce{HCN

ightleftharpoons H+ + CN-}$, producing $\ce{H+}$, so it is an Arrhenius acid.

• $\ce{NH3}$ is a base (produces $\ce{OH-}$ indirectly or accepts $\ce{H+}$), not an acid.
• $\ce{Mg(OH)2}$ is a base (produces $\ce{OH-}$ ions in water: $\ce{Mg(OH)2

ightleftharpoons Mg^{2+} + 2OH-}$).

Answer:

B. HCN