General Chemistry: Acids, Bases, pH, and Biological Molecules

Acids, Bases, and pH in Chemistry

Introduction to Acids and Bases

Acids and bases are fundamental concepts in chemistry, especially relevant to biological systems. Understanding their properties and behavior is essential for interpreting chemical reactions in living organisms.

• Acid: A substance that donates protons (H+) in aqueous solution.

• Base: A substance that accepts protons or donates hydroxide ions (OH-).

• Properties: Acids taste sour, turn blue litmus red, and have pH less than 7. Bases taste bitter, feel slippery, turn red litmus blue, and have pH greater than 7.

• Example: Hydrochloric acid (HCl) is a strong acid; sodium hydroxide (NaOH) is a strong base.

pH Scale and Measurement

The pH scale quantifies the acidity or basicity of a solution. It is a logarithmic scale ranging from 0 (most acidic) to 14 (most basic), with 7 being neutral.

• pH Definition: $pH = -\log_{10}[H^+]

• Measurement: pH can be measured using pH paper, pH meters, or natural indicators such as red cabbage juice extract.

• Application: pH is crucial in biological fluids like blood, urine, and gastric juice.

• Example: Blood has a pH around 7.4; gastric juice is highly acidic (pH ~2).

Neutralization Reactions

Neutralization occurs when an acid reacts with a base to form water and a salt. This process is important in maintaining pH balance in biological systems.

• General Equation: $\text{Acid} + \text{Base} \rightarrow \text{Salt} + \text{Water}$

• Example: $\mathrm{HCl} + \mathrm{NaOH} \rightarrow \mathrm{NaCl} + \mathrm{H_2O}$

Types of Chemical Bonds

Chemical bonds are the forces holding atoms together in molecules and compounds. The main types are ionic, covalent, and hydrogen bonds.

• Ionic Bond: Transfer of electrons from one atom to another, forming ions (e.g., NaCl).

• Covalent Bond: Sharing of electron pairs between atoms (e.g., H2O).

• Hydrogen Bond: Weak attraction between a hydrogen atom and an electronegative atom (e.g., between water molecules).

Organic Compounds and Biological Molecules

Organic Compounds and Hydrocarbons

Organic compounds are primarily made of carbon and hydrogen. Hydrocarbons are the simplest organic compounds, consisting only of these two elements.

• Hydrocarbons: Classified as alkanes, alkenes, and alkynes based on the type of carbon-carbon bonds.

• Example: Methane (CH4) is the simplest hydrocarbon.

Carbohydrates

Carbohydrates are essential biomolecules that provide energy and structural support in living organisms.

• Monosaccharides: Simple sugars (e.g., glucose, fructose).

• Disaccharides: Two monosaccharides joined together (e.g., sucrose, lactose).

• Polysaccharides: Long chains of monosaccharides (e.g., starch, cellulose, glycogen).

• General Formula: $(CH_2O)_n$

Lipids

Lipids are a diverse group of hydrophobic molecules, including fats, oils, and phospholipids. They are important for energy storage and membrane structure.

• Triglycerides: Composed of glycerol and three fatty acids.

• Phospholipids: Major components of cell membranes.

• Steroids: Lipids with a characteristic four-ring structure (e.g., cholesterol).

Amino Acids and Proteins

Amino acids are the building blocks of proteins, which perform a vast array of functions in cells.

• Amino Acid Structure: Central carbon, amino group, carboxyl group, hydrogen atom, and R group (side chain).

• Protein Structure: Proteins are polymers of amino acids linked by peptide bonds.

• Functions: Enzymes, structural support, transport, signaling.

Cell Structure and Function (Biological Context)

Cell Theory and Types of Cells

The cell is the basic unit of life. Cell theory states that all living things are composed of cells, and all cells arise from pre-existing cells.

• Unicellular: Organisms made of a single cell (e.g., bacteria).

• Colonial: Groups of identical cells living together.

• Multicellular: Organisms composed of many specialized cells (e.g., plants, animals).

Cell Organelles and Their Functions

Cells contain specialized structures called organelles, each with specific functions.

• Nucleus: Contains genetic material (DNA).

• Mitochondria: Site of cellular respiration and energy production.

• Chloroplasts: Site of photosynthesis in plant cells.

• Endoplasmic Reticulum (ER): Synthesizes proteins and lipids.

• Golgi Apparatus: Modifies, sorts, and packages proteins.

• Lysosomes: Contain digestive enzymes.

Prokaryotic vs. Eukaryotic Cells

Cells are classified as prokaryotic or eukaryotic based on the presence of a nucleus and membrane-bound organelles.

Feature	Prokaryotic Cell	Eukaryotic Cell
Nucleus	Absent	Present
Organelles	Few, not membrane-bound	Many, membrane-bound
Examples	Bacteria, Archaea	Plants, Animals, Fungi, Protists

Plant vs. Animal Cells

Plant and animal cells share many features but also have key differences.

Feature	Plant Cell	Animal Cell
Cell Wall	Present	Absent
Chloroplasts	Present	Absent
Vacuole	Large central	Small or absent
Shape	Rectangular	Round/Irregular

Cell Transport Mechanisms

Passive and Active Transport

Cells regulate the movement of substances across their membranes through passive and active transport mechanisms.

• Passive Transport: Movement of molecules from high to low concentration without energy input (e.g., diffusion, osmosis, facilitated diffusion).

• Active Transport: Movement of molecules against a concentration gradient, requiring energy (ATP).

• Examples: Sodium-potassium pump (active), oxygen diffusion (passive).

Endocytosis and Exocytosis

Cells use endocytosis and exocytosis to transport large molecules or particles across the membrane.

• Endocytosis: Process by which cells engulf substances into a pouch which becomes a vesicle.

• Exocytosis: Process by which cells expel materials using vesicles that fuse with the plasma membrane.

Solutions and Tonicity

Solutions can be classified based on their solute concentration relative to the cell, affecting water movement.

• Solution: A homogeneous mixture of solute and solvent.

• Solvent: The substance in which the solute dissolves (usually water in biological systems).

• Solute: The substance dissolved in the solvent.

• Tonicity: Describes the relative concentration of solutes in two solutions separated by a membrane.

• Types:

  • Isotonic: Equal solute concentration; no net water movement.

  • Hypotonic: Lower solute concentration outside the cell; water enters the cell.

  • Hypertonic: Higher solute concentration outside the cell; water leaves the cell.

Comparison of Tonicity Effects

Solution Type	Effect on Animal Cell	Effect on Plant Cell
Isotonic	No change	No change
Hypotonic	Swells, may burst	Turgid (normal)
Hypertonic	Shrinks (crenates)	Plasmolyzed

Additional info: Some context and definitions were inferred to provide a self-contained study guide suitable for General Chemistry students, as the original notes were in outline form.