Unit 4 Chemistry in the Environment

Unit 4 Chemistry in the Environment

Acids, Bases, and Salts

Definitions

• Acids: Proton donors / electron acceptors.

• Bases: Proton acceptors / electron donors.

Characteristics

• Acids:

  • Turn blue litmus to red.

  • Sour in taste.

  • pH range: 0-6.

• Bases:

  • Turn red litmus to blue.

  • Bitter in taste.

  • pH range: 8-14.

Classification

• Acids:

  • Monoacidic (Monobasic)

  • Diacidic (Dibasic)

  • Triacidic (Tribasic)

• Bases:

  • Monobasic

  • Dibasic

  • Tribasic

Strength

• Strong Acids: Completely dissociate in solution.

• Weak Acids: Partially dissociate.

• Strong Bases: Completely dissociate in solution.

• Weak Bases: Partially dissociate.

Chemical Properties

• Reactions:

  • Acid + Metal carbonate/Metal ➔ Salt + Hydrogen

  • Acid + Metal ➔ Salt + Hydrogen gas

  • Non-metal oxide + Base ➔ Metal oxide + Acid ➔ Salt + Water

Examples of Acids and Bases

• Common Acids: 1M HCl, Vinegar, Rainwater, Gastric juice.

• Common Bases: Baking soda, Ammonia, Sodium hydroxide.

Properties of Acids and Bases

Key Properties

• pH: Acids < 7, Bases > 7

• Taste: Acids are sour, Bases are bitter

• Electrical Conductivity: Variable based on concentration

• Feel: Weak acids are wet/sticky; strong bases are slippery

• Litmus Test:

  • Acids turn litmus red.

  • Bases turn it blue.

• Phenolphthalein: Colourless in acids, pink in bases.

• Bromothymol Blue: Yellow in acids, blue in bases.

Reactions with Acids and Bases

• Reaction with Metals:

  • Acids react with metals above hydrogen in activity series, producing hydrogen gas.

  • Example: Zn + 2 HCl ➔ ZnCl2 + H2.

• Reaction with Carbonates:

  • Produces carbon dioxide in neutralization reactions.

  • Example: Na2CO3 + HCl ➔ H2CO3 + NaCl ➔ H2O + CO2 + NaCl.

Theoretical Acid-Base Definitions

Definitions

• Arrhenius Theory: Acids produce H+ ions in water; Bases produce OH- ions.

• Bronsted-Lowry Theory: Acids are proton donors; Bases are proton acceptors.

• Lewis Theory: Acids are electron pair acceptors; Bases are electron pair donors.

Arrhenius Theory of Acids and Bases

• Ionization of Acids:

  • Acids ionize in water, producing H+.

  • Example: H2SO4(aq) ➔ 2H+(aq) + SO4^2-(aq).

• Dissociation of Bases:

  • Bases dissociate in water, producing OH-.

  • Example: Ca(OH)2(aq) ➔ Ca2+(aq) + 2OH-(aq).

Neutralization Reactions

Examples

• Write ionization for HCl: HCl(aq) ➔ H+(aq) + Cl-(aq).

• Write dissociation for NaOH: NaOH(aq) ➔ Na+(aq) + OH-(aq).

• Combined reaction:

  • NaOH + HCl ➔ NaCl + H2O.

  • Net ionic: OH-(aq) + H+(aq) ➔ H2O(l).

Strong and Weak Acids and Bases

Characteristics

• Strong Acids/Bases: Fully ionize in solution, resulting in low/high pH and high reactivity.

• Weak Acids/Bases: Partially ionize, with only a small percentage leading to limited ion availability (approx. 2%).

pH Scale

Overview

• pH scale ranges from 0-14:

  • Acids: pH 0-6.

  • Bases: pH 8-14.

  • Neutral: pH 7.

• Change of 1 pH unit equates to a 10x change in acidity or basicity.

Water as an Acid or Base

• Water acts as both acid and base:

  • Reaction: H2O(l) + H2O(l) ↔ H3O+(aq) + OH-(aq).

• Aqueous solutions contain both ions; the balance determines acidity:

  • [H3O+] > [OH-] ➔ acidic.

  • [H3O+] = [OH-] ➔ neutral.

  • [H3O+] < [OH-] ➔ basic.

pH and pOH Relationship

Definitions

• pH = -log[H+].

• pOH = -log[OH-].

• Relationship: [H+] x [OH-] = 10^-14, pH + pOH = 14.

Acid-Base Stoichiometry

Overview

• Initial reading and final reading in a titration indicate how much titrant was used.

• Titration is performed with a standardized solution to find the unknown concentration.

Titration Process

• Titrant: The solution of known concentration.

• Equivalence Point: When neutralization is complete, based on mole ratio.

Example of Titration

Calculation Steps

1. Calculate average volume of titrant used, excluding overshot trials.

2. Convert mL to L.

3. Write balanced equation (e.g. H2SO4 + 2NaOH → Na2SO4 + 2H2O).

4. Find number of moles from titrant used.

5. Use the mole ratio for unknown solution moles.

6. Calculate concentration of unknown solution.

Water Softening

Definitions

• Hard Water: High concentrations of Ca2+ and Mg2+.

• Soft Water: Low concentrations of Ca2+ and Mg2+.

• The reactions may lead to the formation of sediment such as soap scum.

Water Contamination Types

Types

1. Physical Contaminants:

• Floating debris, suspended particles, oils.

2. Biological Contaminants:

• Bacteria, viruses, protozoa (e.g. E. coli).

3. Chemical Contaminants:

• Industrial chemicals, leachate from landfills.

Establishing Water Quality

• Coordination between all levels of government ensures clean drinking water.

• Maximum Acceptable Concentrations (MAC): Levels of substances listed in ppm for safety and aesthetics.

Gasses in the Environment

Composition

• 78% Nitrogen, 21% Oxygen, 0.9% Argon, 0.037% CO2.

The Atmosphere

• Acts as a blanket, trapping heat; essential for life.

Ozone Layer

• Located in the stratosphere; protects from harmful UV radiation.

• Formation: O2 and UV light produce O3.

CFCs and Their Impact

• CFCs deplete ozone; phased out by the Montreal Protocol in 1987.

Structure of the Atmosphere

Layers

1. Exosphere: Outer layer.

2. Thermosphere: Absorbs solar radiation.

3. Mesosphere: Burns up meteors.

4. Stratosphere: Contains ozone layer.

5. Troposphere: Weather occurs here.

Air Pollutants

Definitions

• Any gas/particle that harms organisms/environments.

• Sources: Natural (volcanoes) and anthropogenic (industrial emissions).

Types of Air Pollutants

1. Carbon Monoxide (CO): From burning fossil fuels.

2. Nitrogen Oxides (NOx): From vehicle exhausts, biomass burning.

3. Particulate Matter (PM): From various sources including volcanic.

4. Sulfur Dioxide (SO2): From burning fossil fuels.

5. Volatile Organic Compounds (VOCs): From industrial processes.

Acid Precipitation

• Rainwater's natural acidity (pH 5.6) from CO2 forming carbonic acid.

Air Quality Health Index (AQHI)

• Scale from 1 to 10+ indicating risk levels and health messages for outdoor activities.