Question

Microscopic imperfections in glass are usually harmless, but imperfections of nickel(II) sulfide can cause the glass to crack spontaneously. To study this process, nickel(II) sulfide can be synthesized from sodium sulfide and nickel(II) sulfate. $$ \begin{array}{r} \mathrm{Ni}^{2+}(a q)+\mathrm{SO}_{4}^{2-}(a q)+2 \mathrm{Na}^{+}(a q)+\mathrm{S}^{2-}(a q) \longrightarrow \\ \mathrm{NiS}(s)+2 \mathrm{Na}^{+}(a q)+\mathrm{SO}_{4}^{2-}(a q) \end{array} $$ Which are the spectator ions? Write the net ionic equation.

Short answer

\(\mathrm{Na}^{+}\) and \(\mathrm{SO}_{4}^{2-}\) are the spectator ions. The net ionic equation is \(\mathrm{Ni}^{2+}(aq) + \mathrm{S}^{2-}(aq) \longrightarrow \mathrm{NiS}(s)\).

Step-by-step solution

Identify the Reactants and Products

Review the given chemical equation and distinguish between the reactants and the products. Reactants are the starting substances, and products are the substances formed in the reaction. Reactants in the equation are \(\mathrm{Ni}^{2+}(aq)\), \(\mathrm{SO}_{4}^{2-}(aq)\), \(2\mathrm{Na}^{+}(aq)\) and \(\mathrm{S}^{2-}(aq)\), while the products are \(\mathrm{NiS}(s)\), \(2\mathrm{Na}^{+}(aq)\), and \(\mathrm{SO}_{4}^{2-}(aq)\).

Identify the Spectator Ions

Spectator ions are ions that appear in exactly the same form on both the reactant and product sides of the chemical equation and do not participate in the reaction. By comparing reactants and products, identify \(\mathrm{Na}^{+}\) and \(\mathrm{SO}_{4}^{2-}\) as spectator ions since they do not change during the reaction.

Write the Net Ionic Equation

Eliminate the spectator ions from the complete ionic equation to write the net ionic equation. The net ionic equation only includes the ions and compounds that undergo a chemical change. After canceling out the spectator ions, the net ionic equation is: \[\mathrm{Ni}^{2+}(aq) + \mathrm{S}^{2-}(aq) \longrightarrow \mathrm{NiS}(s)\]

Key concepts

Spectator Ions

In the realm of chemistry, understanding the role of spectator ions can significantly simplify the study of reactions.

Spectator ions are akin to observers at a sports game; they are present but don't participate in the action. Specifically, these ions remain unchanged and do not take part in the actual chemical reaction. They can be found in a solution where a reaction takes place, but they do not contribute to the formation of the product.

Noticing spectator ions in chemical equations is essential because it allows you to simplify the equation to what's known as the net ionic equation. This stripped-down equation only features the particles that undergo a chemical change, thereby giving a clearer view of the reaction's core transformation. For instance, in the synthesis of nickel(II) sulfide from sodium sulfide and nickel(II) sulfate, the sodium (Na+) and the sulfate (SO4^2-) ions appear unchanged on both sides of the equation. As such, they are labeled as spectator ions.

Identifying spectator ions can be mastered by comparing the reactants and products and noting which ions are present in the same form on both sides of the chemical equation. Doing so helps focus on the essentials and provides a deeper insight into the heart of the reaction, as seen in the provided exercise.

Chemical Reactions

Chemical reactions are the backbone of chemistry, involving the transformation of substances into different compounds or elements. These reactions occur when reactant molecules or ions interact to form new products. The process involves breaking old bonds and forming new ones, which translates to changes in energy, often observable as heat, light, or colour change.

In the exercise example, we observe a chemical reaction where nickel(II) ions react with sulfide ions to create nickel(II) sulfide, a compound with very different properties compared to the reactants. Chemical reactions are governed by the laws of conservation of mass and charge. This means that while atoms can be rearranged in a reaction, the total number of each type of atom, and the total charge, remains the same before and after the reaction.

When studying chemical reactions, it is crucial to understand the mechanisms and the conditions under which the reaction occurs. Variables such as temperature, concentration, and the presence of catalysts can significantly influence the reaction's rate and outcome. In educational settings, mastering the art of balancing equations and recognizing reaction patterns is a foundational skill for students. The provided exercise encourages this skill development by prompting students to derive the net ionic equation from the full chemical equation.

Ionic Compounds

Ionic compounds are substances consisting of positively and negatively charged ions held together by the strong force of ionic bonds. These bonds form when atoms transfer electrons between each other, resulting in a positive ion (cation) and a negative ion (anion). Ionic compounds are commonly formed from metals and nonmetals, with the metal losing electrons to become a cation and the nonmetal gaining electrons to become an anion.

Characteristics of ionic compounds include high melting and boiling points and the ability to conduct electricity when dissolved in water or melted, which makes them integral to countless chemical processes. For example, in the exercise provided, nickel(II) sulfide (NiS) is an ionic compound that forms when nickel(II) ions (Ni2+) and sulfide ions (S2-) react with each other.

Understanding the nature of ionic compounds is vital for being able to predict the outcome of reactions involving them. In aqueous solutions, these compounds often dissociate into their constituent ions, which can then participate in the reaction as active components or simply present as spectator ions, playing no direct role in the chemical change at hand. The dissociation into ions is a key concept when dealing with reactions in solution, further emphasizing the importance of ionic compounds in understanding chemistry.