Exam 2 Review Guide: Acids & Bases, Redox Reactions, Organic Chemistry, Polymers, and Nuclear Chemistry

Acids and Bases

Chemical and Physical Properties of Acids and Bases

Acids and bases are two fundamental classes of compounds in chemistry, distinguished by their characteristic properties and behaviors in solution.

• Acids: Taste sour, turn litmus paper red, react with metals to produce hydrogen gas, and conduct electricity in solution.

• Bases: Taste bitter, feel slippery, turn litmus paper blue, and also conduct electricity in solution.

Arrhenius and Bronsted-Lowry Definitions

Acids and bases can be defined in several ways, most commonly by the Arrhenius and Bronsted-Lowry theories.

• Arrhenius Acid: Produces H+ ions in aqueous solution.

• Arrhenius Base: Produces OH- ions in aqueous solution.

• Bronsted-Lowry Acid: Donates a proton (H+).

• Bronsted-Lowry Base: Accepts a proton (H+).

Strong and Weak Acids and Bases

The strength of an acid or base refers to its degree of ionization in water.

• Strong Acids/Bases: Completely ionize in solution (e.g., HCl, NaOH).

• Weak Acids/Bases: Partially ionize in solution (e.g., acetic acid, ammonia).

pH and Acidity/Basicity

The pH scale measures the concentration of hydrogen ions in a solution, indicating its acidity or basicity.

• pH Formula:

$\text{pH} = -\log_{10}[\text{H}^+]$

• pH < 7: Acidic

• pH = 7: Neutral

• pH > 7: Basic

Buffers

A buffer is a solution that resists changes in pH when small amounts of acid or base are added.

• Buffers typically consist of a weak acid and its conjugate base.

• They are important in biological systems to maintain stable pH.

Redox Reactions

Oxidation and Reduction

Redox reactions involve the transfer of electrons between substances.

• Oxidation: Loss of electrons.

• Reduction: Gain of electrons.

Oxidizing and Reducing Agents

• Oxidizing Agent: Causes oxidation by accepting electrons (is reduced).

• Reducing Agent: Causes reduction by donating electrons (is oxidized).

Electrochemical Cells (Batteries)

Electrochemical cells convert chemical energy into electrical energy through redox reactions.

• Consist of two electrodes (anode and cathode) and an electrolyte.

• Used in batteries to power devices.

Corrosion: Iron Rusting

Corrosion is a redox process where metals react with environmental substances.

• Iron rusts when it reacts with oxygen and water, forming iron(III) oxide.

Common Oxidizing Agents

• Hydrogen peroxide (H2O2)

• Potassium permanganate (KMnO4)

• Chlorine (Cl2)

Redox Reactions in Life

• Photosynthesis: Plants convert CO2 and H2O into glucose and O2 using sunlight.

• Food Metabolism: Cells extract energy from food via redox reactions.

Organic Chemistry: Hydrocarbons and Functional Groups

Hydrocarbons

Hydrocarbons are compounds composed solely of carbon and hydrogen.

• Alkanes: Single bonds (saturated hydrocarbons).

• Alkenes: At least one double bond (unsaturated).

• Alkynes: At least one triple bond (unsaturated).

Functional Groups

Functional groups are specific groups of atoms within molecules that determine the chemical properties of those molecules.

• Carboxylic Acids: Contain -COOH group; acidic; e.g., acetic acid.

• Esters: Contain -COOR group; often fragrant; e.g., ethyl acetate.

• Alcohols: Contain -OH group; e.g., ethanol.

Halogenated Hydrocarbons

Halogenated hydrocarbons contain halogen atoms (Cl, Br, F, I) and can be toxic or environmentally hazardous.

• Examples: Chloroform, DDT.

• Can cause health and environmental issues.

Polymers

Polymers and Monomers

Polymers are large molecules made from repeating units called monomers.

• Monomer: Small molecule that can join with others to form a polymer.

• Polymer: Large molecule formed from many monomers.

Natural Polymers

• Cellulose (plant cell walls)

• Starch (energy storage in plants)

• Proteins (chemically modified: gelatin)

Thermoplastics vs. Thermosetting Polymers

• Thermoplastics: Can be melted and reshaped; e.g., polyethylene.

• Thermosetting: Harden permanently after being set; e.g., Bakelite.

Cross-Linking

Cross-linking involves forming bonds between polymer chains, increasing strength and rigidity.

• Cross-linked polymers are less flexible and more durable.

Glass Transition Temperature

The glass transition temperature is the temperature at which a polymer changes from a hard, glassy state to a soft, rubbery state.

• Important for determining polymer applications.

Nuclear Chemistry

Sources and Dangers of Radiation

Natural radiation comes from cosmic rays, radioactive minerals, and radon gas. Ionizing radiation can damage living tissue.

• Alpha, beta, gamma radiation are types of ionizing radiation.

• Exposure can cause health risks such as cancer.

Balancing Nuclear Equations

Nuclear equations must conserve mass number and atomic number.

• Example:

$\text{^{14}_{6}C} \rightarrow \text{^{14}_{7}N} + \text{e}^-$

Decay Products

• Alpha decay: emits He nucleus ($\text{^{4}_{2}He}$)

• Beta decay: emits electron ($\text{e}^-$)

• Gamma decay: emits high-energy photon ($\gamma$)

Half-Life and Radioisotopic Dating

The half-life is the time required for half of a radioactive sample to decay.

• Half-life formula:

$N = N_0 \left( \frac{1}{2} \right)^{\frac{t}{t_{1/2}}}$

• Used in dating ancient materials (e.g., carbon-14 dating).

Nuclear Transmutation

Nuclear transmutation is the conversion of one element into another via nuclear reactions.

• Example: Bombarding nitrogen with alpha particles produces oxygen.

Applications of Radioisotopes

• Medical imaging (e.g., PET scans)

• Radiation therapy

• Industrial tracers

Blocking Radiation

Type of Radiation	Material Needed to Block
Alpha	Paper, skin
Beta	Plastic, glass, aluminum
Gamma	Lead, thick concrete

Fission vs. Fusion

• Fission: Splitting of heavy nuclei (e.g., uranium) to release energy.

• Fusion: Combining light nuclei (e.g., hydrogen) to form heavier nuclei; releases more energy than fission.

Hazardous Fallout Isotopes

• Strontium-90

• Iodine-131

• Cesium-137

Uses and Consequences of Nuclear Energy

• Used for electricity generation.

• Produces radioactive waste.

• Risk of accidents and environmental contamination.

Background Radiation

Background radiation is the constant, low-level radiation present in the environment from natural and artificial sources.

• Includes cosmic rays, radon, and medical procedures.