Problem 24 - Chemistry: The Central Science

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) \(\mathrm{Cr}_{2}\left(\mathrm{SO}_{4}\right)_{3}(\mathrm{aq})+\left(\mathrm{NH}_{4}\right)_{2} \mathrm{CO}_{3}(a q) \longrightarrow\) (b) \(\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}(a q)+\mathrm{K}_{2} \mathrm{SO}_{4}(a q) \longrightarrow\) (c) \(\mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{2}(a q)+\mathrm{KOH}(a q) \longrightarrow\)

Step-by-Step Solution

Answer

(a) Balanced net ionic equation: \(2Cr^{3+}(aq) + 3SO_4^{2-}(aq) \longrightarrow 2Cr(OH)_3(s)\); Spectator ions: \(6NH_4^+\) and \(3CO_3^{2-}\) (b) Balanced net ionic equation: \(Ba^{2+}(aq) + SO_4^{2-}(aq) \longrightarrow BaSO_4(s)\); Spectator ions: \(2K^+\) and \(2NO_3^-\) (c) Balanced net ionic equation: \(Fe^{2+}(aq) + 2OH^-(aq) \longrightarrow Fe(OH)_2(s)\); Spectator ions: \(2K^+\) and \(2NO_3^-\)

Step 1: Balanced Molecular Equation

First, we need to write the balanced molecular equation for the reaction: \(Cr_{2}(SO_4)_3(aq) + 3(NH_4)_2CO_3(aq) \longrightarrow 2Cr(OH)_3(s) + 6NH_4^+(aq) + 3CO_3^{2-}(aq)\) #Step 2: Identify Strong Electrolytes#

Step 2: Strong Electrolytes Identification

The strong electrolytes in the reaction are the soluble ionic compounds and strong acids or bases. In this case, the strong electrolytes are \(Cr_2(SO_4)_3\) and \((NH_4)_2CO_3\). #Step 3: Ionic Equation#

Step 3: Writing the Ionic Equation

Next, we write the ionic equation by breaking the strong electrolytes into their constituent ions: \[2Cr^{3+}(aq) + 3SO_4^{2-}(aq) + 6NH_4^+(aq) + 3CO_3^{2-}(aq) \longrightarrow 2Cr(OH)_3(s) + 6NH_4^+(aq) + 3CO_3^{2-}(aq)\] #Step 4: Identify and Remove Spectator Ions#

Step 4: Identifying and Removing Spectator Ions

Spectator ions are the ions that are present on both sides of the equation and do not participate in the reaction. In this case, the spectator ions are \(6NH_4^+\) and \(3CO_3^{2-}\). We remove these ions from both sides of the equation. #Step 5: Balanced Net Ionic Equation#

Step 5: Balanced Net Ionic Equation for Reaction (a)

After removing the spectator ions, we are left with the balanced net ionic equation: \[2Cr^{3+}(aq) + 3SO_4^{2-}(aq) \longrightarrow 2Cr(OH)_3(s)\] #b. Ba(NO₃)₂(aq) + K₂SO₄(aq) -># #Step 1: Balanced Molecular Equation#

Step 6: Balanced Molecular Equation

First, we need to write the balanced molecular equation for the reaction: \(Ba(NO_3)_2(aq) + K_2SO_4(aq) \longrightarrow BaSO_4(s) + 2KNO_3(aq)\) #Step 2: Identify Strong Electrolytes#

Step 7: Strong Electrolytes Identification

The strong electrolytes in the reaction are the soluble ionic compounds and strong acids or bases. In this case, the strong electrolytes are \(Ba(NO_3)_2\) and \(K_2SO_4\). #Step 3: Ionic Equation#

Step 8: Writing the Ionic Equation

Next, we write the ionic equation by breaking the strong electrolytes into their constituent ions: \[Ba^{2+}(aq) + 2NO_3^-(aq) + 2K^+(aq) + SO_4^{2-}(aq) \longrightarrow BaSO_4(s) + 2K^+(aq) + 2NO_3^-(aq)\] #Step 4: Identify and Remove Spectator Ions#

Step 9: Identifying and Removing Spectator Ions

Spectator ions are the ions that are present on both sides of the equation and do not participate in the reaction. In this case, the spectator ions are \(2K^+\) and \(2NO_3^-\). We remove these ions from both sides of the equation. #Step 5: Balanced Net Ionic Equation#

Step 10: Balanced Net Ionic Equation for Reaction (b)

After removing the spectator ions, we are left with the balanced net ionic equation: \[Ba^{2+}(aq) + SO_4^{2-}(aq) \longrightarrow BaSO_4(s)\] #c. Fe(NO₃)₂(aq) + KOH(aq) -># #Step 1: Balanced Molecular Equation#

Step 11: Balanced Molecular Equation

First, we need to write the balanced molecular equation for the reaction: \(Fe(NO_3)_2(aq) + 2KOH(aq) \longrightarrow Fe(OH)_2(s) + 2KNO_3(aq)\) #Step 2: Identify Strong Electrolytes#

Step 12: Strong Electrolytes Identification

The strong electrolytes in the reaction are the soluble ionic compounds and strong acids or bases. In this case, the strong electrolytes are \(Fe(NO_3)_2\) and \(KOH\). #Step 3: Ionic Equation#

Step 13: Writing the Ionic Equation

Next, we write the ionic equation by breaking the strong electrolytes into their constituent ions: \[Fe^{2+}(aq) + 2NO_3^-(aq) + 2K^+(aq) + 2OH^-(aq) \longrightarrow Fe(OH)_2(s) + 2K^+(aq) + 2NO_3^-(aq)\] #Step 4: Identify and Remove Spectator Ions#

Step 14: Identifying and Removing Spectator Ions

Spectator ions are the ions that are present on both sides of the equation and do not participate in the reaction. In this case, the spectator ions are \(2K^+\) and \(2NO_3^-\). We remove these ions from both sides of the equation. #Step 5: Balanced Net Ionic Equation#

Step 15: Balanced Net Ionic Equation for Reaction (c)

After removing the spectator ions, we are left with the balanced net ionic equation: \[Fe^{2+}(aq) + 2OH^-(aq) \longrightarrow Fe(OH)_2(s)\]

Key Concepts

Spectator Ions

Spectator ions are ions that appear on both sides of a chemical equation but don't partake in the reaction itself. They're present in the reaction mixture but remain unchanged. When dealing with ionic equations, identifying spectator ions is crucial because they can be "cancelled out" to give the net ionic equation, which reflects the actual chemical change happening in the solution.
For example, in a reaction between barium nitrate and potassium sulfate, which forms a precipitate of barium sulfate, the spectator ions are potassium (\(K^+\)) and nitrate (\(NO_3^-\)) ions. These ions start as ions in the solution and remain the same, making them unreactive in the process. Discovering spectator ions leads to a simplified view of the chemical change happening, showcasing only the substances that actually react to form the final product.

Balanced Molecular Equations

Writing a balanced molecular equation is the fundamental step in understanding chemical reactions. It displays the reactants and products in their molecular form. The equation needs to reflect the law of conservation of mass, meaning the number of each type of atom on the reactants side must equal the number on the products side.
For instance, in the reaction of ferric nitrate with potassium hydroxide, the balanced molecular equation is:
\[Fe(NO_3)_2(aq) + 2KOH(aq) \longrightarrow Fe(OH)_2(s) + 2KNO_3(aq)\]
This equation indicates that one molecule of iron(II) nitrate reacts with two molecules of potassium hydroxide to produce solid iron(II) hydroxide and two molecules of potassium nitrate. Each element appears with the same number of atoms on both sides, confirming the reaction is balanced.

Strong Electrolytes Identification

Strong electrolytes are substances that fully dissociate into ions when dissolved in water. Knowing which compounds are strong electrolytes is essential for writing accurate ionic equations. Most soluble ionic compounds and strong acids or bases fall under this category.
Taking the example of chromium sulfate and ammonium carbonate in solution, each compound separates into ions completely, i.e., chromium sulfate into chromium and sulfate ions, and ammonium carbonate into ammonium and carbonate ions. Recognizing strong electrolytes allows us to express reactions in ionic forms, focusing on the interaction of the ions themselves rather than the entire compounds.

Ionic Equations

Ionic equations illustrate a reaction in terms of ions present in the solution. These equations are a step beyond molecular equations as they break down soluble strong electrolytes into their respective ions. The key outcome is the net ionic equation, which excludes spectator ions and highlights the essence of the chemical reaction.
For example, in the reaction between iron nitrate and potassium hydroxide forming iron hydroxide, the ionic equation is:
\[Fe^{2+}(aq) + 2OH^-(aq) \longrightarrow Fe(OH)_2(s)\]
This equation emphasizes the interaction between iron and hydroxide ions leading to the formation of solid iron(II) hydroxide, the true reaction happening in solution. Understanding ionic equations helps one explore the core of chemical interactions beyond surface-level transformations.