Problem 26 - Chemistry: The Central Science in SI Units, Global Edition

Question

Write balanced net ionic equations for the reactions that occur in each of the following cases. Identify the spectator ion or ions in each reaction. (a) \(\mathrm{Ba}(\mathrm{OH})_{2}(a q)+\mathrm{FeCl}_{3}(a q) \longrightarrow\) (b) \(\mathrm{ZnCl}_{2}(a q)+\mathrm{Cs}_{2} \mathrm{CO}_{3}(a q) \longrightarrow\) (c) \(\mathrm{Na}_{2} \mathrm{~S}(a q)+\operatorname{CoSO}_{4}(a q) \longrightarrow\)

Step-by-Step Solution

Answer

(a) The balanced net ionic equation for case (a) is: \(2OH^-(aq) + Fe^{3+}(aq) \longrightarrow 2Fe(OH)_3(s)\). The spectator ions are \(Ba^{2+}\) and \(Cl^-\). (b) The balanced net ionic equation for case (b) is: \(Zn^{2+}(aq) + CO_3^{2-}(aq) \longrightarrow ZnCO_3(s)\). The spectator ions are \(Cs^+\) and \(Cl^-\). (c) The balanced net ionic equation for case (c) is: \(S^{2-}(aq) + Co^{2+}(aq) \longrightarrow CoS(s)\). The spectator ions are \(Na^+\) and \(SO_4^{2-}\).

Step 1: Write Molecular Equation - a

Write the molecular equation for the given reaction: \(Ba(OH)_2(aq) + FeCl_3(aq) \longrightarrow\)

Step 2: Predict Products and Balance the Equation - a

In this reaction, we will have a double replacement reaction. The products will be \(BaCl_2\) and \(Fe(OH)_3\). Balancing the equation, we get: \(Ba(OH)_2(aq) + FeCl_3(aq) \longrightarrow BaCl_2(aq) + 2Fe(OH)_3(s)\)

Step 3: Dissociate Strong Electrolytes - a

Now dissociate all strong electrolytes in the reaction: \(Ba^{2+}(aq) + 2OH^-(aq) + Fe^{3+}(aq) + 3Cl^-(aq) \longrightarrow Ba^{2+}(aq) + 2Cl^-(aq) + 2Fe(OH)_3(s)\)

Step 4: Cancel Spectator Ions - a

Identify and cancel spectator ions in this reaction. The spectator ions are \(Ba^{2+}\) and \(Cl^-\), so: \(2OH^-(aq) + Fe^{3+}(aq) \longrightarrow 2Fe(OH)_3(s)\) (b)

Step 5: Write Molecular Equation - b

Write the molecular equation for the given reaction: \(ZnCl_2(aq) + Cs_2CO_3(aq) \longrightarrow\)

Step 6: Predict Products and Balance the Equation - b

In this reaction, we will have a double replacement reaction. The products will be \(ZnCO_3\) and \(CsCl\). Balancing the equation, we get: \(ZnCl_2(aq) + Cs_2CO_3(aq) \longrightarrow ZnCO_3(s) + 2CsCl(aq)\)

Step 7: Dissociate Strong Electrolytes - b

Now dissociate all the strong electrolytes in the reaction: \(Zn^{2+}(aq) + 2Cl^-(aq) + 2Cs^+(aq) + CO_3^{2-}(aq) \longrightarrow ZnCO_3(s) + 2Cs^+(aq) + 2Cl^-(aq)\)

Step 8: Cancel Spectator Ions - b

Identify and cancel spectator ions in this reaction. The spectator ions are \(Cs^+\) and \(Cl^-\), so: \(Zn^{2+}(aq) + CO_3^{2-}(aq) \longrightarrow ZnCO_3(s)\) (c)

Step 9: Write Molecular Equation - c

Write the molecular equation for the given reaction: \(Na_2S(aq) + CoSO_4(aq) \longrightarrow\)

Step 10: Predict Products and Balance the Equation - c

In this reaction, we will have a double replacement reaction. The products will be \(Na_2SO_4\) and \(CoS\). Balancing the equation, we get: \(Na_2S(aq) + CoSO_4(aq) \longrightarrow Na_2SO_4(aq) + CoS(s)\)

Step 11: Dissociate Strong Electrolytes - c

Now dissociate all the strong electrolytes in the reaction: \(2Na^+(aq) + S^{2-}(aq) + Co^{2+}(aq) + SO_4^{2-}(aq) \longrightarrow 2Na^+(aq) + SO_4^{2-}(aq) + CoS(s)\)

Step 12: Cancel Spectator Ions - c

Identify and cancel spectator ions in this reaction. The spectator ions are \(Na^+\) and \(SO_4^{2-}\), so: \(S^{2-}(aq) + Co^{2+}(aq) \longrightarrow CoS(s)\)

Key Concepts

Spectator Ions

Spectator ions play an intriguing role in chemical reactions. They are ions that remain unchanged during the course of the chemical reaction and do not participate in the formation of the product.
Think of them like spectators at a sporting event; they observe without affecting the outcome of the game.
In net ionic equations, we specifically focus on the reaction's active participants by omitting spectator ions from the equation, leaving only those ions involved in forming the product. This adjustment simplifies the equation, making the reaction clearer by spotlighting what truly changes.

• Examples of spectator ions from the exercises include \(Ba^{2+}\), \(Cl^-\), \(Cs^+\), and \(SO_4^{2-}\).
• They are present before and after the reaction, without any change in their chemical state.
• Naming them helps understand which species are directly involved in the reaction.

This approach of identifying and excluding spectator ions can help students better understand the essential chemistry of the reaction.

Double Replacement Reactions

Double replacement reactions are fascinating processes where two compounds exchange components to form two new compounds.
In these reactions, the cations and anions of two different molecules swap places, leading to the formation of new products.
For example, when \(Ba(OH)_2\) reacts with \(FeCl_3\), the \(Ba\) and \(Fe\) ions exchange partners, resulting in \(BaCl_2\) and \(Fe(OH)_3\).

• The basic form of the reaction is \(AB + CD \longrightarrow AD + CB\).
• The reaction is often instantaneous and driven by the formation of a solid, gas, or weak electrolyte like water.
• In the exercise provided, reactions (a), (b), and (c) describe such transformations, emphasizing the importance of balancing the resulting equations.

Understanding double replacement reactions is crucial as it lays the foundation for predicting the products of chemical reactions.

Strong Electrolytes

Strong electrolytes are substances that completely dissociate into ions when dissolved in water.
These ions enable the solution to conduct electricity very efficiently, hence the name "strong electrolyte."
Typical examples include most salts, strong acids, and strong bases, such as \(HCl\), \(NaCl\), and \(NaOH\).

• In the net ionic equations given, strong electrolytes like \(Ba(OH)_2\), \(FeCl_3\), and \(ZnCl_2\) are dissociated into their constituent ions.
• This leads to a detailed examination of the ions actively participating in a reaction.
• Recognizing strong electrolytes is important in achieving accurate chemical equations and predicting the behavior of solutions.

By understanding which substances are strong electrolytes, students can better analyze and predict reaction behaviors in aqueous solutions.