Properties of Water and Acids/Bases

Definition: A hydrogen bond is the attraction between an atom that has a partial positive charge (typically hydrogen) and an atom that has a partial negative charge (usually oxygen or nitrogen).

Definition: Adhesion occurs when water molecules stick to other polar molecules.
Principle: "Likes dissolve likes", meaning polar molecules prefer to associate with other polar molecules while nonpolar molecules associate with other nonpolar molecules.
Example: Water adheres to plant cell walls, aiding in water transport.

Water exhibits cohesion, a phenomenon where water molecules are attracted to each other due to hydrogen bonding.
This property allows water to create droplets and is vital for processes such as water transportation in plants.

Hydration of Water Movement: The arrangement of water molecules (H₂O) and their interaction with each other and other substances govern movement in biological systems.

Hydrogen Bonds in Ice: Hydrogen bonds in ice are stable, maintaining a structured lattice which results in lower density compared to liquid water.

Hydrogen Bonds in Liquid Water: In liquid form, water's hydrogen bonds break and reform continually, allowing for characteristics such as flow and adaptability in different environments.

Cohesion: Water molecules hold together due to hydrogen bonds, vital for various biological functions.
High Specific Heat: Water can absorb a large amount of heat without changing temperature significantly, due to hydrogen bonds absorbing heat when breaking.
High Heat of Vaporization: Many hydrogen bonds must be broken for water to evaporate, providing a cooling effect.
Lower Density of Ice: Ice’s structure places molecules further apart, allowing it to float and insulate aquatic environments.
Solubility: Water’s polarity makes it an excellent solvent, with polar molecules attracted to water enabling chemical reactions in living organisms.

Solution: A homogeneous mixture of two or more substances, with properties depending on the solute and solvent.
- Solvent: The medium that dissolves the solute (usually a liquid).
- Solute: The substance being dissolved.
- Aqueous Solution: When water acts as the solvent, it is often called an aqueous solution.
- Universal Solvent: Water is referred to as the universal solvent because of its ability to dissolve many substances.

Water’s polarity enables it to function effectively as a solvent for polar substances and ions.
- Hydrophilic: Polar molecules or parts of molecules that are attracted to water (e.g., ions, sugars).
- Hydrophobic: Nonpolar molecules repelled by water, leading to phenomena like aggregation known as hydrophobic interactions (e.g., oils, fats, wax).

Water molecules can ionize, resulting in hydroxide ions (OH⁻) and hydrogen ions (H⁺, also called protons).

Acids: Substances that donate H⁺ ions in a solution.
- Example: Hydrochloric acid (HCl) ionizes in water to produce H⁺ and Cl⁻ ions.
Bases: Substances that accept H⁺ ions.
- Example: Ammonia (NH₃) reacts with H⁺ to form ammonium ions (NH₄⁺).
- Sodium hydroxide (NaOH) completely ionizes in water into Na⁺ and OH⁻ ions.

Definition: A measure of the acidity or alkalinity of a solution, based on hydrogen ion concentration ([H⁺]).
Scale Range: 0-14, where 7 is neutral, less than 7 is acidic, and greater than 7 is basic.
Each unit change in pH represents a tenfold difference in H⁺ concentration.
- Example: Shifting from pH 7 to pH 5 indicates 100 times more H⁺ ions.
Common pH values:
- Liquid drain cleaner: pH = 14
- Ammonia: pH = 10.5-11.5
- Blood: pH = 7.4
- Lemon juice: pH = 2

Definition: Buffers help maintain pH stability by accepting H⁺ ions when excess is present and donating H⁺ ions when depleted.
Many buffers in biological systems consist of weak acids and their conjugate bases.

Carbonic Acid (H₂CO₃) can dissociate into bicarbonate (HCO₃⁻) and a hydrogen ion (H⁺).
The reverse reaction can also occur to maintain pH balance:
- HCO₃⁻ + H⁺ ⇌ H₂CO₃

Definition: Proteins are long chains of amino acids folded into complex three-dimensional shapes, predominantly held together by weak bonds (hydrogen bonds, ionic bonds).
Role of Proteins: Many are enzymes that catalyze chemical reactions crucial for biological processes.
The stability of protein structure can be influenced by changes in pH, which may alter bonding patterns.