Question

Write ionic and net ionic equations for the following reactions: (a) \(\mathrm{Na}_{2} \mathrm{~S}(a q)+\mathrm{ZnCl}_{2}(a q) \longrightarrow\) (b) \(\mathrm{K}_{3} \mathrm{PO}_{4}(a q)+3 \mathrm{Sr}\left(\mathrm{NO}_{3}\right)_{2}(a q) \longrightarrow\) (c) \(\mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2}(a q)+2 \mathrm{NaOH}(a q) \longrightarrow\)

Short answer

a) Net Ionic Equation : \(\mathrm{S^{2-}(aq) + Zn^{2+}(aq)} \longrightarrow\)b) Net Ionic Equation : \(\mathrm{PO_{4}^{3-}(aq) + 3Sr^{2+}(aq)} \longrightarrow\)c) Net Ionic Equation : \(\mathrm{Mg^{2+}(aq) + 2OH^{-}(aq)} \longrightarrow\)

Step-by-step solution

Ionic and Net Ionic Equations

Ionic Equations are equations that show all the compounds in ionic form. Net Ionic Equations are equations that only show the key substances involved in the reaction. A rule to remember, all soluble ionic compounds and strong acids dissociate into their ions in solution.

Problem a: \(\mathrm{Na}_{2} \mathrm{~S}(a q)+\mathrm{ZnCl}_{2}(a q) \longrightarrow\)

First, break down the reactants in ionic form and this is the full ionic equation:\(\mathrm{2Na^{+}(aq) + S^{2-}(aq) + Zn^{2+}(aq) + 2Cl^{-}(aq)} \longrightarrow\)Next, the net ionic equation is generated by removing spectator ions, ions which occur in the same form on both sides of the equation. These are \(Na^{+}\) and \(Cl^{-}\).Hence, the net ionic equation is \(\mathrm{S^{2-}(aq) + Zn^{2+}(aq)} \longrightarrow\)

Problem b: \(\mathrm{K}_{3} \mathrm{PO}_{4}(a q)+3 \mathrm{Sr}\left(\mathrm{NO}_{3}\right)_{2}(a q) \longrightarrow\)

Start with the full ionic equation:\(\mathrm{3K^{+}(aq) + PO_{4}^{3-}(aq) + 3Sr^{2+}(aq) + 6NO_{3}^{-}(aq)} \longrightarrow\)Remove the spectator ions, which are \(K^{+}\) and \(NO_{3}^{-}\), to get the net ionic equation:\(\mathrm{PO_{4}^{3-}(aq) + 3Sr^{2+}(aq)} \longrightarrow\)

Problem c: \(\mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2}(a q)+2 \mathrm{NaOH}(a q) \longrightarrow\)

Break down the reactants into ions for the full ionic equation:\(\mathrm{Mg^{2+}(aq) + 2NO_{3}^{-}(aq) + 2Na^{+}(aq) + 2OH^{-}(aq)} \longrightarrow\)Remove the spectator ions, here again, \(Na^{+}\) and \(NO_{3}^{-}\), to find the net ionic equation:\(\mathrm{Mg^{2+}(aq) + 2OH^{-}(aq)} \longrightarrow\)

Key concepts

Net Ionic Equations

A net ionic equation is a streamlined version of a chemical equation. It highlights the key substances involved in the reaction. Unlike the full ionic equation that lists out all the ions present, the net ionic equation removes spectator ions. Spectator ions are ions that do not participate directly in the chemical reaction.

To write a net ionic equation, you first need the complete ionic equation. Then, by identifying and excluding the ions unchanged on both sides of the equation, you reduce it to the vital components. This yields the net ionic equation.

For example, consider a situation involving sodium sulfide (\( \mathrm{Na}_{2} \mathrm{~S} \)).

• Full Ionic Equation: \( \mathrm{2Na^{+}(aq) + S^{2-}(aq) + Zn^{2+}(aq) + 2Cl^{-}(aq)} \longrightarrow \)
• Net Ionic Equation: Remove \( \mathrm{Na^{+}} \) and \( \mathrm{Cl^{-}} \) (spectator ions) to get \( \mathrm{S^{2-}(aq) + Zn^{2+}(aq)} \longrightarrow \)

Chemical Reactions

Chemical reactions are processes where substances (reactants) transform into different substances (products). In aqueous solutions, many compounds dissociate into ions. This is especially true for ionic compounds and strong acids, which completely break down into their respective ions when dissolved in water.

During a chemical reaction, these ions may recombine to form a product. However, not all ions take part in the reaction.

• Dissociation: Compounds break down into their respective ions.
• Reaction: Ions that participate in forming new compounds.

Reactions in the aqueous phase often result in ionic and net ionic equations, showing how compounds dissociate and react in water. Understanding the dissociation and recombination helps in predicting reaction products and writing correct chemical equations.

Spectator Ions

Spectator ions are a notable concept in chemistry. These ions exist in the solution but don't directly participate in the reaction occurring. They're essential in maintaining charge neutrality and providing the environment for reactions, although they don’t affect the actual outcome.

For instance, when exploring chemical equations for reactions that occur in water, you’ll often find ions that appear unchanged on both sides of the equation. It's these ions that are considered 'spectator ions.'

• They maintain electrical balance.
• They do not participate in the chemical change.

For example, in a reaction involving potassium phosphate (\( \mathrm{K}_{3} \mathrm{PO}_{4} \)), the \( \mathrm{K^{+}} \) ions among others might be spectator ions, meaning they do not transform but simply exist in the aqueous solution.