General Chemistry Exam 3 Study Guide

Review of Previous Exam Material

This section covers foundational concepts necessary for success in general chemistry, including measurement, chemical nomenclature, and basic chemical reactions.

• SI Units and Prefixes: Know the metric prefixes from mega (106) to nano (10-9). For example, 1 megameter (Mm) = 106 meters; 1 nanometer (nm) = 10-9 meters.

• Volume Conversion: 1 milliliter (mL) = 1 cubic centimeter (cm3).

• Significant Figures: Use correct significant figures in all calculations. Significant figures reflect the precision of measured values.

• Diatomic Elements: Seven elements exist naturally as diatomic molecules: H2, N2, O2, F2, Cl2, Br2, I2.

• Ionic vs. Molecular Compounds: Ionic compounds consist of metals and nonmetals (e.g., NaCl), while molecular compounds are formed from nonmetals (e.g., CO2).

• Empirical Formulas: The simplest whole-number ratio of atoms in a compound. For example, the empirical formula for glucose (C6H12O6) is CH2O.

• Naming Ionic Compounds: Include polyatomic ions (e.g., SO42-) and transition metals (use Roman numerals for charge).

• Naming Binary Molecular Compounds: Use prefixes (mono-, di-, tri-, etc.) up to deca- (10).

• Balancing Chemical Equations: Ensure the same number of atoms of each element on both sides of the equation.

• Molar Mass: The mass of one mole of a substance, used to convert between grams and moles. Formula:

Stoichiometry

Stoichiometry involves quantitative relationships between reactants and products in a chemical reaction.

• Relating Quantities: Use balanced equations to relate moles and masses of reactants and products.

• Limiting Reagent: The reactant that is completely consumed first, limiting the amount of product formed.

• Excess Reagent: The reactant that remains after the reaction is complete.

• Percent Yield: Measures the efficiency of a reaction. Formula:

• Example: If 10 g of product is obtained but the theoretical yield is 12 g, percent yield is .

Solutions and Molarity

Solutions are homogeneous mixtures; molarity is a measure of concentration.

• Molarity (M): Defined as moles of solute per liter of solution. Formula:

• Calculating Concentrations: Determine concentrations of formula units, specific ions, and total ions in a solution.

• Preparing Solutions: Dissolve a known amount of solute in solvent and dilute to a desired volume.

• Using Molarity in Calculations: Convert between moles, grams, and solution volume using molarity.

• Dilution: Process of reducing concentration by adding solvent. Formula:

• Example: To prepare 250 mL of 0.1 M NaCl from 1.0 M stock, use , so L = 25 mL.

Stoichiometry in Solution Reactions

Apply stoichiometry to reactions in solution, such as precipitation and neutralization.

• Precipitation Reactions: Occur when two solutions combine to form an insoluble product (precipitate).

• Neutralization Reactions: Acid reacts with base to form water and a salt.

• Using Molarity: Calculate moles and mass of reactants/products from solution volumes and concentrations.

Electrolytes and Dissolution Processes

Electrolytes are substances that produce ions in solution; their strength depends on the degree of ionization.

• Strong Electrolytes: Completely dissociate in water (e.g., NaCl, HCl).

• Weak Electrolytes: Partially ionize (e.g., acetic acid, NH3).

• Nonelectrolytes: Do not produce ions (e.g., sugar, ethanol).

• Dissolution Processes:

  • Strong Acids: Complete ionization.

  • Weak Acids/Bases: Partial ionization; equilibrium arrows used in equations.

  • Soluble Ionic Compounds: Dissociate to produce ions.

  • Nonelectrolytes: Simple dissolution, no ions produced.

• Writing Dissolution Equations: Write complete and balanced equations for dissolution of ionic compounds, acids, bases, and molecular compounds.

Precipitation Reactions (Metathesis/Double Displacement)

Precipitation reactions involve the exchange of ions between two compounds, resulting in the formation of an insoluble product.

• Solubility Rules: Used to predict whether a compound will dissolve in water.

• Predicting Products: Identify possible products and determine if a precipitate forms.

• Writing Equations:

  • Molecular Equation: Shows reactants and products as compounds.

  • Complete Ionic Equation: Shows all soluble ionic substances as ions.

  • Net Ionic Equation: Shows only the ions and molecules directly involved in the reaction; spectator ions are omitted.

• Spectator Ions: Ions that do not participate in the reaction.

• Example: Mixing AgNO3 and NaCl forms AgCl (precipitate):

  • Molecular: AgNO3 (aq) + NaCl (aq) → AgCl (s) + NaNO3 (aq)

  • Complete Ionic: Ag+ (aq) + NO3- (aq) + Na+ (aq) + Cl- (aq) → AgCl (s) + Na+ (aq) + NO3- (aq)

  • Net Ionic: Ag+ (aq) + Cl- (aq) → AgCl (s)

Acids and Bases

Acids and bases are classified by their strength and their behavior in solution.

• Strong Acids: Seven strong acids to know: HCl, HBr, HI, HNO3, HClO4, HClO3, H2SO4.

• Strong Bases: Typically group 1 and 2 hydroxides (e.g., NaOH, KOH, Ca(OH)2).

• Identifying Acids: Acids have H at the front of the formula (e.g., HCl).

• Dissolution Representation:

  • Strong Acids: Complete dissociation:

  • Weak Acids: Partial dissociation with equilibrium:

Neutralization Reactions

Neutralization is a type of double displacement reaction where an acid reacts with a base to produce water and a salt.

• Predicting Products: Combine H+ from acid and OH- from base to form H2O; remaining ions form a salt.

• Writing Equations:

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

  • Complete Ionic Equation: H+ (aq) + Cl- (aq) + Na+ (aq) + OH- (aq) → Na+ (aq) + Cl- (aq) + H2O (l)

  • Net Ionic Equation: H+ (aq) + OH- (aq) → H2O (l)

Reference Materials

A periodic table and solubility rules will be provided during the exam. Use these resources to identify element properties and predict solubility in reactions.

Table: Classification of Electrolytes

Table: Seven Strong Acids

Additional info: This guide expands on brief points from the content guide, providing academic context and examples for each topic. It is structured to help students review key concepts for Exam 3 in CHEM105.