Question

Which of the following is not included in the net ionic equation for the reaction between $CaC{l}_2$ and $N{a}_{2}C{O}_3$ to form calcium carbonate and sodium chloride?

• A. $C{a}^{2+}$
• B. $C{O}_3^{2-}$
• C. $2N{a}^{+}$
• D. $CaC{O}_3$
• E. All of the above

Answer 1

The correct option is C $2N{a}^{+}$

The overall reaction is :

$CaC{l}_2\left(aq\right)+N{a}_{2}C{O}_3\left(aq\right)\to CaC{O}_3\left(s\right)+2NaCl\left(aq\right)$

A net ionic equation is an equation representing the actual reaction that occurs during a precipitation reaction, leaving out the spectator ions.

Since the $N{a}^{+}$ and $C{l}^{-}$ ions are ionized in solution both before and after the reaction, and they remain unchanged by the reaction, one can infer that they do not actually take part in the reaction at all. Instead, they hang out in the aqueous solution and watch the other two ions, $C{a}^{2+}$ and $C{O}_3^{2-}$, react with one another. For this reason, the $N{a}^{+}$ and $C{l}^{-}$ ions are called spectator ions. For the calcium carbonate precipitation reaction, the net ionic equation looks like this:

$C{a}^{2+}\left(aq\right)+C{O}_3^{2-}\left(aq\right)\to CaC{O}_3\left(s\right)$

The spectator ions are not represented because, they do not take part in the reaction. Only the ions, that react with one another and the form precipitate, are represented in a net ionic equation.