Question

4.26 write balanced net ionic equations for the reactions that occur in each of the following cases. identify the spectator ion or ions in each reaction.
(a) cr₂(so₄)₃(aq) + (nh₄)₂co₃(aq) →
(b) ba(no₃)₂(aq) + k₂so₄(aq) →
(c) fe(no₃)₂(aq) + koh(aq) →

Explanation:

Step1: Write total ionic equations

(a) The total ionic equation for $\mathrm{Cr}_{2}(\mathrm{SO}_{4})_{3}(aq)+3(\mathrm{NH}_{4})_{2}\mathrm{CO}_{3}(aq)\to \mathrm{Cr}_{2}(\mathrm{CO}_{3})_{3}(s)+3(\mathrm{NH}_{4})_{2}\mathrm{SO}_{4}(aq)$ is $2\mathrm{Cr}^{3 +}(aq)+3\mathrm{SO}_{4}^{2 -}(aq)+6\mathrm{NH}_{4}^{+}(aq)+3\mathrm{CO}_{3}^{2 -}(aq)\to\mathrm{Cr}_{2}(\mathrm{CO}_{3})_{3}(s)+6\mathrm{NH}_{4}^{+}(aq)+3\mathrm{SO}_{4}^{2 -}(aq)$.
(b) The total ionic equation for $\mathrm{Ba}(\mathrm{NO}_{3})_{2}(aq)+\mathrm{K}_{2}\mathrm{SO}_{4}(aq)\to\mathrm{BaSO}_{4}(s)+2\mathrm{KNO}_{3}(aq)$ is $\mathrm{Ba}^{2 +}(aq)+2\mathrm{NO}_{3}^{-}(aq)+2\mathrm{K}^{+}(aq)+\mathrm{SO}_{4}^{2 -}(aq)\to\mathrm{BaSO}_{4}(s)+2\mathrm{K}^{+}(aq)+2\mathrm{NO}_{3}^{-}(aq)$.
(c) The total ionic equation for $\mathrm{Fe}(\mathrm{NO}_{3})_{2}(aq)+2\mathrm{KOH}(aq)\to\mathrm{Fe}(\mathrm{OH})_{2}(s)+2\mathrm{KNO}_{3}(aq)$ is $\mathrm{Fe}^{2 +}(aq)+2\mathrm{NO}_{3}^{-}(aq)+2\mathrm{K}^{+}(aq)+2\mathrm{OH}^{-}(aq)\to\mathrm{Fe}(\mathrm{OH})_{2}(s)+2\mathrm{K}^{+}(aq)+2\mathrm{NO}_{3}^{-}(aq)$.

Step2: Cancel out spectator ions to get net - ionic equations

(a) Canceling out $6\mathrm{NH}_{4}^{+}(aq)$ and $3\mathrm{SO}_{4}^{2 -}(aq)$ on both sides, the net - ionic equation is $2\mathrm{Cr}^{3 +}(aq)+3\mathrm{CO}_{3}^{2 -}(aq)\to\mathrm{Cr}_{2}(\mathrm{CO}_{3})_{3}(s)$. Spectator ions are $\mathrm{NH}_{4}^{+}$ and $\mathrm{SO}_{4}^{2 -}$.
(b) Canceling out $2\mathrm{K}^{+}(aq)$ and $2\mathrm{NO}_{3}^{-}(aq)$ on both sides, the net - ionic equation is $\mathrm{Ba}^{2 +}(aq)+\mathrm{SO}_{4}^{2 -}(aq)\to\mathrm{BaSO}_{4}(s)$. Spectator ions are $\mathrm{K}^{+}$ and $\mathrm{NO}_{3}^{-}$.
(c) Canceling out $2\mathrm{K}^{+}(aq)$ and $2\mathrm{NO}_{3}^{-}(aq)$ on both sides, the net - ionic equation is $\mathrm{Fe}^{2 +}(aq)+2\mathrm{OH}^{-}(aq)\to\mathrm{Fe}(\mathrm{OH})_{2}(s)$. Spectator ions are $\mathrm{K}^{+}$ and $\mathrm{NO}_{3}^{-}$.

Answer:

(a) Net - ionic equation: $2\mathrm{Cr}^{3 +}(aq)+3\mathrm{CO}_{3}^{2 -}(aq)\to\mathrm{Cr}_{2}(\mathrm{CO}_{3})_{3}(s)$; Spectator ions: $\mathrm{NH}_{4}^{+}$, $\mathrm{SO}_{4}^{2 -}$
(b) Net - ionic equation: $\mathrm{Ba}^{2 +}(aq)+\mathrm{SO}_{4}^{2 -}(aq)\to\mathrm{BaSO}_{4}(s)$; Spectator ions: $\mathrm{K}^{+}$, $\mathrm{NO}_{3}^{-}$
(c) Net - ionic equation: $\mathrm{Fe}^{2 +}(aq)+2\mathrm{OH}^{-}(aq)\to\mathrm{Fe}(\mathrm{OH})_{2}(s)$; Spectator ions: $\mathrm{K}^{+}$, $\mathrm{NO}_{3}^{-}$