Question

which compound is a base?
○ a. hcn
○ b. naf
○ c. (ce{ca(oh)2})
○ d. (ce{ch3cooh})

Explanation:

To determine which compound is a base, we use the definition of a base (Arrhenius base: produces $\ce{OH^-}$ ions in solution; Bronsted - Lowry base: accepts $\ce{H^+}$).

• Option A: $\ce{HCN}$ (hydrocyanic acid) is an acid as it donates $\ce{H^+}$.
• Option B: $\ce{NaF}$ is a salt (formed from a strong base $\ce{NaOH}$ and a weak acid $\ce{HF}$), and in solution, $\ce{F^-}$ hydrolyzes to make the solution basic, but $\ce{NaF}$ itself is not a base (it is a salt that acts as a base - former).
• Option C: $\ce{Ca(OH)_2}$ is a strong base. It dissociates in water as $\ce{Ca(OH)_2 -> Ca^{2+} + 2OH^-}$, producing hydroxide ions, so it fits the definition of a base.
• Option D: $\ce{CH_3COOH}$ (acetic acid) is a weak acid as it donates $\ce{H^+}$.

Answer:

C. $\ce{Ca(OH)2}$