Problem 48 - Chemistry and Chemical Reactivity

Question

Write balanced net ionic equations for the following reactions: (a) the reaction of aqueous solutions of silver nitrate and sodium iodide (b) the reaction of aqueous solutions of barium chloride and potassium carbonate

Step-by-Step Solution

Answer

(a) \(\text{Ag}^+ + \text{I}^- \rightarrow \text{AgI}(s)\) (b) \(\text{Ba}^{2+} + \text{CO}_3^{2-} \rightarrow \text{BaCO}_3(s)\)

Step 1: Write the Molecular Equation

For reaction (a), the molecular equation is: \[ \text{AgNO}_3(aq) + \text{NaI}(aq) \rightarrow \text{AgI}(s) + \text{NaNO}_3(aq) \]For reaction (b), the molecular equation is: \[ \text{BaCl}_2(aq) + \text{K}_2\text{CO}_3(aq) \rightarrow \text{BaCO}_3(s) + 2 \text{KCl}(aq) \].

Step 2: Write the Complete Ionic Equation

For reaction (a), dissociate all aqueous compounds:\[ \text{Ag}^+(aq) + \text{NO}_3^-(aq) + \text{Na}^+(aq) + \text{I}^-(aq) \rightarrow \text{AgI}(s) + \text{Na}^+(aq) + \text{NO}_3^-(aq) \]For reaction (b):\[ \text{Ba}^{2+}(aq) + 2\text{Cl}^-(aq) + 2\text{K}^+(aq) + \text{CO}_3^{2-}(aq) \rightarrow \text{BaCO}_3(s) + 2\text{K}^+(aq) + 2\text{Cl}^-(aq) \].

Step 3: Identify and Remove Spectator Ions

For reaction (a), the spectator ions are \( \text{Na}^+(aq) \) and \( \text{NO}_3^-(aq) \). For reaction (b), the spectator ions are \( \text{K}^+(aq) \) and \( \text{Cl}^-(aq) \).

Step 4: Write the Net Ionic Equation

For reaction (a), removing the spectator ions gives:\[ \text{Ag}^+(aq) + \text{I}^-(aq) \rightarrow \text{AgI}(s) \].For reaction (b), removing the spectator ions gives:\[ \text{Ba}^{2+}(aq) + \text{CO}_3^{2-}(aq) \rightarrow \text{BaCO}_3(s) \].

Key Concepts

Silver Nitrate Reaction

The reaction involving silver nitrate is a common example of a precipitation reaction, where a solid forms from the mixture of two solutions. When aqueous solutions of silver nitrate (AgNO₃) and sodium iodide (NaI) are combined, a chemical reaction occurs. Silver nitrate dissociates into silver ions (Ag⁺) and nitrate ions (NO₃⁻). Sodium iodide dissociates into sodium ions (Na⁺) and iodide ions (I⁻). When the Ag⁺ ions encounter the I⁻ ions, they combine to form a precipitate of silver iodide (AgI), an insoluble solid. The molecular equation for this reaction describes the substances involved before they separate into ions:- \(\text{AgNO}_3(aq) + \text{NaI}(aq) \rightarrow \text{AgI}(s) + \text{NaNO}_3(aq)\) Understanding this reaction helps in learning how ionic compounds can interact to form new compounds, sometimes resulting in a visible product, like a solid precipitate.

Barium Chloride Reaction

In the barium chloride reaction, solutions of barium chloride (BaCl₂) and potassium carbonate (K₂CO₃) are mixed, resulting in the formation of a solid product. When both compounds dissolve in water, they dissociate into their respective ions. Barium chloride separates into barium ions (Ba²⁺) and chloride ions (Cl⁻), while potassium carbonate dissociates into potassium ions (K⁺) and carbonate ions (CO₃²⁻). When Ba²⁺ and CO₃²⁻ ions meet, they form the insoluble compound barium carbonate (BaCO₃), which precipitates from the solution. The reaction is described by the following molecular equation:- \(\text{BaCl}_2(aq) + \text{K}_2\text{CO}_3(aq) \rightarrow \text{BaCO}_3(s) + 2 \text{KCl}(aq)\)This equation shows the initial compounds and the resulting products, illustrating how soluble ions can react to form an insoluble product in a chemical reaction.

Spectator Ions

In many chemical reactions, some ions do not participate in forming the final product. These are known as spectator ions. They remain unchanged and only "observe" the reaction taking place. In the silver nitrate and sodium iodide reaction, spectator ions are sodium ions (Na⁺) and nitrate ions (NO₃⁻), since they do not influence the formation of the silver iodide precipitate. In the barium chloride and potassium carbonate reaction, potassium ions (K⁺) and chloride ions (Cl⁻) are the spectator ions. - Spectator ions: - Are present in the solutions but do not participate in forming the precipitate. - Are not included in the net ionic equation. - Help in balancing the charges in the complete ionic equation. Understanding spectator ions is key to simplifying reactions down to their core reactive components, highlighting what actually participates in the formation of a new compound.

Molecular Equation

A molecular equation provides a detailed representation of the reactants and products in a chemical reaction. It displays all the compounds involved in their whole form without breaking them down into their ions. This form of the equation offers a clear picture of what substances are combined and what products form through the reaction.Taking reaction (a) as an example, the molecular equation - \(\text{AgNO}_3(aq) + \text{NaI}(aq) \rightarrow \text{AgI}(s) + \text{NaNO}_3(aq)\)clearly states that silver nitrate and sodium iodide react to form silver iodide and sodium nitrate. The molecular equation for reaction (b) is:- \(\text{BaCl}_2(aq) + \text{K}_2\text{CO}_3(aq) \rightarrow \text{BaCO}_3(s) + 2 \text{KCl}(aq)\)These equations help students understand the starting materials and the produced compounds, serving as a vital step before decomposing the solution into ionic forms, eventually leading to the net ionic equation.