Question

according to the brønsted-lowry definitions of acids and bases, which of the following compounds is both an acid and a base?

hclo3

koh

h2s

h2o

ca(oh)2

Explanation:

According to the Brønsted - Lowry definitions, an acid is a proton donor and a base is a proton acceptor.

• $\ce{HClO3}$: It can only donate protons (acts as an acid), for example, $\ce{HClO3 + H2O

ightarrow H3O+ + ClO3-}$.

• $\ce{KOH}$: It dissociates to give $\ce{K+}$ and $\ce{OH-}$, and $\ce{OH-}$ can accept protons (acts as a base), but it cannot donate protons in the Brønsted - Lowry sense.
• $\ce{H2S}$: It can donate protons (acts as an acid), like $\ce{H2S + H2O

ightarrow H3O+ + HS-}$, but it is not a good proton acceptor.

• $\ce{H2O}$: It can donate a proton (act as an acid) $\ce{H2O + NH3

ightarrow NH4+ + OH-}$ and also can accept a proton (act as a base) $\ce{H2O + HCl
ightarrow H3O+ + Cl-}$.

• $\ce{Ca(OH)2}$: It dissociates to give $\ce{Ca^{2 + }}$ and $\ce{OH-}$, and $\ce{OH-}$ can accept protons (acts as a base), but it cannot donate protons in the Brønsted - Lowry sense.

Answer:

$\ce{H2O}$