Problem 118 - Introductory Chemistry Atoms First

Question

Indicate whether a precipitate forms when these solutions are mixed, and write the formula of the precipitate if one forms: (a) Silver nitrate and potassium iodide (b) Lithium sulfate and silver acetate (c) Sodium chloride and ammonium sulfate

Step-by-Step Solution

Answer

(a) Yes, a precipitate forms. Formula of the precipitate: AgI (b) Yes, a precipitate forms. Formula of the precipitate: Ag₂SO₄ (c) No precipitate forms.

Step 1: Know the solubility rules

To predict the formation of precipitates, we need to know the solubility rules. Some common solubility rules are: 1. All nitrates are soluble. 2. All acetates are soluble. 3. Most sulfates are soluble. 4. Most chlorides, bromides, and iodides are soluble, except those of silver, lead, and mercury. 5. Most carbonates, phosphates, and silicates are insoluble. Now let's apply these rules to our problems.

Step 2: (a) Silver nitrate and potassium iodide

Write down the reactants and their ions: Silver nitrate (AgNO3): Ag⁺ and NO₃⁻ Potassium iodide (KI): K⁺ and I⁻ Considering possible ion combinations for the products: AgI and KNO₃. According to the solubility rules, iodides are generally soluble except for silver, lead, and mercury. Therefore, AgI is insoluble and will form a precipitate. KNO₃ is soluble because all nitrates are soluble. The balanced chemical equation is: AgNO₃(aq) + KI(aq) → AgI(s) + KNO₃(aq) A precipitate forms: Yes Formula of the precipitate: AgI

Step 3: (b) Lithium sulfate and silver acetate

Write down the reactants and their ions: Lithium sulfate (Li2SO4): 2 Li⁺ and SO₄²⁻ Silver acetate (AgC2H3O2): Ag⁺ and C₂H₃O₂⁻ Considering possible ion combinations for the products: LiC₂H₃O₂ and Ag₂SO₄. According to solubility rules, all acetates are soluble, so LiC₂H₃O₂ is soluble. Most sulfates are soluble, but silver sulfate (Ag₂SO₄) is an exception and is insoluble. Therefore, Ag₂SO₄ will form a precipitate. The balanced chemical equation is: Li₂SO₄(aq) + 2 AgC₂H₃O₂(aq) → 2 LiC₂H₃O₂(aq) + Ag₂SO₄(s) A precipitate forms: Yes Formula of the precipitate: Ag₂SO₄

Step 4: (c) Sodium chloride and ammonium sulfate

Write down the reactants and their ions: Sodium chloride (NaCl): Na⁺ and Cl⁻ Ammonium sulfate ((NH₄)₂SO₄): 2 NH₄⁺ and SO₄²⁻ Considering possible ion combinations for the products: Na₂SO₄ and NH₄Cl. Most sulfates are soluble, and sodium sulfate (Na₂SO₄) is no exception. Most chlorides are soluble, and ammonium chloride (NH₄Cl) is no exception. The balanced chemical equation is: 2 NaCl(aq) + (NH₄)₂SO₄(aq) → Na₂SO₄(aq) + 2 NH₄Cl(aq) A precipitate forms: No Formula of the precipitate: no precipitate

Key Concepts

Solubility Rules

Understanding solubility rules is crucial for determining whether a precipitation reaction will occur. These rules provide guidelines on what types of ionic compounds are soluble or insoluble when dissolved in water. Here are some simplified solubility rules to keep in mind:

• Nitrates and Acetates: Nitrates (\(NO_3^−\)) and acetates often form soluble compounds, making them good candidates to stay dissolved in solution.
• Chlorides, Bromides, and Iodides: These halides are usually soluble, except when paired with silver, lead, or mercury, which form insoluble compounds like silver iodide (\(AgI\)).
• Sulfates: Sulfates (\(SO_4^{2-}\)) are generally soluble, but exceptions include those of barium, lead, and silver, such as silver sulfate (\(Ag_2SO_4\)).
• Carbonates and Phosphates: These typically form insoluble compounds unless combined with alkali metals or ammonium.

These rules help us predict whether a solid precipitate will form when solutions are mixed. For instance, in a reaction between silver nitrate and potassium iodide, silver iodide will precipitate because it is an insoluble iodide.

Chemical Equations

Chemical equations represent the rearrangement of atoms during a chemical reaction. A correctly balanced equation reflects the conservation of mass and charge, showing the same number of each type of atom on both sides of the equation. Here’s how to write a balanced chemical equation:

• Identify the Reactants and Products: Start by listing the reactants and products. For example, when mixing silver nitrate (\(AgNO_3\)) and potassium iodide (\(KI\)), the products are silver iodide (\(AgI\)) and potassium nitrate (\(KNO_3\)).
• Check Solubility Rules: Determine which compounds will be solid precitates or will remain in solution using solubility rules.
• Balance the Equation: Ensure that each element is balanced. Adjust coefficients as necessary. The equation for the mentioned reaction is:\[AgNO_3(aq) + KI(aq) \rightarrow AgI(s) + KNO_3(aq)\]

Balanced chemical equations are key to understanding the stoichiometry and actual process involved in a reaction.

Ionic Compounds

Ionic compounds are formed from positive and negative ions bonding together due to their opposite charges. They typically consist of metals combining with non-metals. Here are some important features of ionic compounds:

• Formation: Ionic compounds are made when metals lose electrons to become positively charged cations, and non-metals gain electrons to become negatively charged anions.
• Properties: These compounds often have high melting and boiling points because of the strong forces between ions. When dissolved in water or melted, they conduct electricity due to the movement of free ions.
• Examples: Common examples include table salt (\(NaCl\)) and silver nitrate (\(AgNO_3\)). Each compound’s specific properties depend on the ions' charges and sizes.

Understanding ionic compounds is fundamental to predicting outcomes in chemical reactions, such as precipitate formation. Each ionic compound brings specific characteristics to a reaction scenario, influencing whether a compound remains in solution or forms as a solid.