Question

When each of the following pairs of aqueous solutions is mixed, does a precipitation reaction occur? If so, write balanced molecular, total ionic, and net ionic equations. (a) Potassium chloride + iron(III) nitrate (b) Ammonium sulfate + barium chloride

Short answer

No precipitate forms in (a). In (b), the precipitate is BaSO₄.

Step-by-step solution

- Identify the reactants

For each pair of solutions, identify the chemical formulas. (a) Potassium chloride: KCl, Iron(III) nitrate: Fe(NO₃)₃ (b) Ammonium sulfate: (NH₄)₂SO₄, Barium chloride: BaCl₂

- Determine possible products

When mixing the solutions, use double displacement to determine the products:(a) KCl + Fe(NO₃)₃ → KNO₃ + FeCl₃ (b) (NH₄)₂SO₄ + BaCl₂ → BaSO₄ + 2NH₄Cl

- Solubility rules

Apply the solubility rules to determine if any precipitate forms:(a) Both KNO₃ and FeCl₃ are soluble in water, so no precipitation reaction.(b) BaSO₄ is insoluble in water, so it forms a precipitate while NH₄Cl remains soluble.

- Write balanced molecular equation

Write the balanced molecular equation for (b): (NH₄)₂SO₄(aq) + BaCl₂(aq) → BaSO₄(s) + 2NH₄Cl(aq)

- Write total ionic equation

Write the total ionic equation by splitting aqueous compounds into ions:2NH₄⁺(aq) + SO₄²⁻(aq) + Ba²⁺(aq) + 2Cl⁻(aq) → BaSO₄(s) + 2NH₄⁺(aq) + 2Cl⁻(aq)

- Identify and write net ionic equation

Cancel out the spectator ions (ions that appear on both sides) to find the net ionic equation:SO₄²⁻(aq) + Ba²⁺(aq) → BaSO₄(s)

Key concepts

Solubility Rules

When working with precipitation reactions, understanding solubility rules is crucial. Solubility rules help predict whether a compound will dissolve in water (aqueous) or form a solid precipitate. Most compounds containing alkali metal ions (like potassium or sodium) and ammonium ion (NH₄⁺) are soluble. Nitrates (NO₃⁻), acetates (C₂H₃O₂⁻), and most chlorates (ClO₃⁻) are also generally soluble. However, some compounds are insoluble. For example, sulfates (SO₄²⁻) are generally soluble except for those of barium (Ba²⁺), lead (Pb²⁺), and calcium (Ca²⁺). Chlorides are typically soluble, but exceptions like silver chloride (AgCl) exist. Knowing these rules helps determine if a precipitate forms during a chemical reaction.

Double Displacement Reactions

A double displacement reaction, or metathesis, involves the exchange of ions between two compounds. These reactions generally occur in aqueous solutions. The general form is:

AB + CD → AD + CB.

Here, the cations A and C swap places. For example, when mixing potassium chloride (KCl) and iron(III) nitrate (Fe(NO₃)₃), the reaction forms potassium nitrate (KNO₃) and iron(III) chloride (FeCl₃):

KCl + Fe(NO₃)₃ → KNO₃ + FeCl₃.

A double displacement reaction might yield a precipitate if one of the products is insoluble based on solubility rules. In our example, no precipitate forms since both KNO₃ and FeCl₃ are soluble. However, in the reaction between ammonium sulfate ((NH₄)₂SO₄) and barium chloride (BaCl₂), barium sulfate (BaSO₄) forms as a precipitate because it is insoluble in water.

Net Ionic Equations

Net ionic equations simplify reactions by showing only the species that change during the reaction. They help focus on the formation of the precipitate. To write a net ionic equation:

• Write the balanced molecular equation. For ammonium sulfate and barium chloride, it is:
  
  (NH₄)₂SO₄(aq) + BaCl₂(aq) → BaSO₄(s) + 2NH₄Cl(aq).
  
  
• Split aqueous compounds into their ions to write the total ionic equation:
  
  2NH₄⁺(aq) + SO₄²⁻(aq) + Ba²⁺(aq) + 2Cl⁻(aq) → BaSO₄(s) + 2NH₄⁺(aq) + 2Cl⁻(aq).
  
  
• Identify spectator ions (ions that appear on both sides) and cancel them out. Here, NH₄⁺ and Cl⁻ are spectator ions.
• The net ionic equation is:
  
  SO₄²⁻(aq) + Ba²⁺(aq) → BaSO₄(s).
  
  

This equation highlights the formation of the barium sulfate precipitate, which is the key change in the reaction.