Question

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

Short answer

Write balanced ionic and net ionic equations for each reaction.

Step-by-step solution

Identify the Reaction Products

We start by predicting the products of each given reaction:(a) \(\mathrm{Na}_{2} \mathrm{~S}(aq) + \mathrm{ZnCl}_{2}(aq) \rightarrow \mathrm{ZnS}(s) + 2\mathrm{NaCl}(aq)\) (b) \(\mathrm{K}_{3} \mathrm{PO}_{4}(aq) + 3\mathrm{Sr}\left(\mathrm{NO}_{3}\right)_{2}(aq) \rightarrow \mathrm{Sr}_{3}\left(\mathrm{PO}_{4}\right)_{2}(s) + 6\mathrm{KNO}_{3}(aq)\)(c) \(\mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2}(aq) + 2\mathrm{NaOH}(aq) \rightarrow \mathrm{Mg(OH)}_{2}(s) + 2\mathrm{NaNO}_{3}(aq)\)

Key concepts

Net Ionic Equations

Net ionic equations are a simplified way to represent chemical reactions. They only include the components that undergo a change during the reaction. This means excluding spectator ions, which remain unchanged throughout the process.
In the problem given, the goal is to write the net ionic equations for the reactions provided. For reaction (a), the equation is: \[ \text{Zn}^{2+}(aq) + \text{S}^{2-}(aq) \rightarrow \text{ZnS}(s) \]This highlights only the species forming the precipitate, zinc sulfide. After removing the spectator ions (Na⁺ and Cl⁻), one is left with just the ions that form the solid.
Having a net ionic equation allows one to clearly see what is truly occurring in the reaction, emphasizing the significant components without the clutter of ions that do not change.

Precipitation Reactions

Precipitation reactions occur when two aqueous solutions mix to form an insoluble solid, known as the precipitate. These reactions are critical in understanding net ionic equations because they help identify what components remain in solution and what forms a solid.
For instance, in reaction (b), the mixing of potassium phosphate and strontium nitrate results in the formation of strontium phosphate, a solid precipitate:\[ 2\text{PO}_{4}^{3-}(aq) + 3\text{Sr}^{2+}(aq) \rightarrow \text{Sr}_{3}(\text{PO}_{4})_{2}(s) \] Precipitation is useful for isolating certain chemicals or removing impurities. By understanding which combinations of ions create solids, you can better predict and control chemical reactions. These types of reactions help visually demonstrate the changes that occur when different substances combine.

Aqueous Reactions

Aqueous reactions are those happening in water as its solvent. They involve the interaction between soluble ionic compounds, at times leading to the formation of precipitates, gases, or weak electrolytes. In an aqueous solution, many compounds dissociate into ions.
To further clarify using reaction (c), both magnesium nitrate and sodium hydroxide are dissolved in water, forming separate ions. When these ions interact, a new solid forms:\[ \text{Mg}^{2+}(aq) + 2\text{OH}^{-}(aq) \rightarrow \text{Mg(OH)}_{2}(s) \]In this scenario, two solutions that appear to be clear and without distinct particles suddenly form a solid when mixed. Understanding aqueous reactions plays a pivotal role in chemistry due to their prevalence in natural and industrial processes. They can lead to surprising and important results based on the behavior of ions in water.

Chemical Equations

Chemical equations are symbolic representations of chemical reactions. They provide a clear way to show the reactants transforming into products, including the phases of each component. The initial given reactions need to be balanced properly to reflect the conservation of mass and energy.
Each provided reaction is written in a balanced state: - Reaction (a) shows the combination of sodium sulfide and zinc chloride forming zinc sulfide and sodium chloride. - For reaction (b), potassium phosphate reacts with strontium nitrate to yield strontium phosphate and potassium nitrate. - Similarly, reaction (c) results in a mixture of magnesium nitrate and sodium hydroxide forming magnesium hydroxide and sodium nitrate. In chemical equations, balancing means making sure that the number of atoms for each element and the charges are equal on both the reactant and product sides. This balance is essential in accurately conveying the chemical process and reflecting the principle of conservation of mass.