Solution_Stoichiometry

General Chemistry 2 Overview

  • Focus on the properties of solutions, solubility, and stoichiometry in reactions in solutions.

  • Application of energy changes in chemical reactions for calculating enthalpy change.

Learning Targets

  • Ability to perform stoichiometric calculations for reactions in solution.

Lesson 5.1: Precipitation Reactions

Definition

  • Precipitation Reaction: Involves the formation of an insoluble ionic compound when a cation and an anion react.

    • The insoluble product formed is called a precipitate.

Solubility

  • Solubility: The ability of a substance to dissolve in a given amount of solvent at a specific temperature.

  • Example:

    • NaCl: 35.89 g per 100 mL of water at 15°C.

    • BaSO4: 0.0002448 g per 100 mL of water at the same temperature.

Double Displacement Reactions

  • Involves exchanging ions between two reactants to form new compounds.

  • Occurs when an insoluble precipitate or water is produced.

Solubility Rules

Soluble Compounds

  • Exceptions include:

    • Alkali metals, ammonium ion, nitrate, perchlorate, acetate: always soluble.

    • Chlorides, bromides, iodides: soluble except those of Pb²⁺, Ag⁺, Hg₂²⁺.

    • Sulfates: soluble except for Sr²⁺, Ba²⁺, Pb²⁺, Hg₂²⁺.

Insoluble Compounds

  • Carbonates, phosphates: generally insoluble, except those of alkali metals and ammonium ion.

  • Hydroxides: generally insoluble, with exceptions for alkali metals and some alkaline earth metals.

Chemical Equations

Types of Equations

  1. Molecular Equation: Represents all reactants and products as intact compounds.

    • Example: CdSO4(aq) + K2S(aq) → CdS(s) + K2SO4(aq)

  2. Total Ionic Equation: Shows all soluble ionic compounds as ions in solution.

  3. Net Ionic Equation: Eliminates spectator ions from the total ionic equation.

    • Example: Cd²⁺(aq) + S²⁻(aq) → CdS(s)

Real-Life Applications

  • BaSO4: Used in imaging (e.g., X-rays) due to its nontoxic nature and insolubility.

  • Silver Bromide (AgBr): Used in photography due to its ability to develop images upon exposure to light.

  • Washing Soda (Na2CO3): Softens hard water by forming insoluble precipitates with calcium and magnesium ions.

Practice Problems

  • Determine solubility of compounds and verify precipitation reactions by writing balanced chemical equations.

  • Calculate theoretical yields and excess reactants in precipitation reactions.

Acid-Base Reactions

Definitions

  • Acids: Produce hydrogen ions (H⁺) in solution with a sour taste.

  • Bases: Produce hydroxide ions (OH⁻) in solution with a bitter taste and slippery feel.

Neutralization Reactions

  • Classified as double displacement: acid + base → salt + water.

    • Example: HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)

Titration in Quantitative Chemistry

Definition

  • Titration: A technique for determining the concentration of a solution by reacting a known solution with an unknown concentration.

Components

  • Titrant: Solution with known concentration.

  • Analyte: Solution with unknown concentration.

Steps in Titration

  1. Determine the balanced molecular equation.

  2. Measure the moles of titrant used.

  3. Calculate the concentration of the analyte.

Tips and Check Your Understanding

  • Understand the relationship between reactants and products in stoichiometric calculations.

  • Solve theoretical yield problems to reinforce knowledge of how reactants interact in chemical equations.