Hydrogen Bonds: Weak electrostatic attractions between water molecules (between partial positive H and partial negative O of another molecule).

Universal Solvent:

Hydration: Water surrounds ions ($e.g.$, $Na^+$ and $Cl^-$ in $NaCl$) to dissolve them.
Hydrolysis: Water molecule itself breaks ($H_2O \rightleftharpoons H^+ + OH^-$) to break down other molecules.

Acid-Base Balance (Ionic Equilibrium): Water's ability to dissociate into $H^+$ (acidity) and $OH^-$ (alkalinity).

pH Scale: 0-14. <7 acidic, 7 neutral, >7 alkaline.
Salts: Can be acidic, basic, or neutral when dissolved in water, depending on their parent acid and base strength.

Solution: Mixture of solute (dissolved substance) and solvent (dissolving medium).
Concentration: Amount of solute per unit volume of solvent ($g/L$).
Colligative Properties (depend on concentration):
- Vapor Pressure: Pressure exerted by vapor above a liquid. Lower in solutions than pure water.
- Boiling Point: Temperature at which vapor pressure equals atmospheric pressure. Higher in solutions than pure water.
  - Affected by atmospheric pressure (higher altitude $\rightarrow$ lower BP).
- Freezing Point: Temperature at which liquid becomes solid. Lower in solutions than pure water.
  - Solutes interfere with ice crystal formation.
- Osmotic Pressure: Pressure needed to prevent osmosis. Higher in solutions than pure water.
Osmosis: Movement of water across a semipermeable membrane from low solute concentration to high solute concentration.

Density: Mass per unit volume ($g/cm^3$ or $kg/m^3$).
Unique Property: Maximum density at $4^\circ C$.
- As water cools from $4^\circ C$ to $0^\circ C$, it expands, and density decreases.
- Ice is less dense than liquid water, so it floats.
Importance of Ice Floating: Insulates aquatic life in cold regions.
Salinity: Higher salinity (more dissolved salts) increases water density.
Hydrometer: Device used to measure liquid density.
Ocean Currents: Driven by differences in water density (due to temperature and salinity), and water pressure.

Heat: Form of energy (measured in Joules).
Temperature: Measure of hotness or coldness (measured in $^\circ C$, K, $^\circ F$).
- $K = ^\circ C + 273$.
- $^\circ F = (1.8 \times ^\circ C) + 32$.
Specific Heat: Amount of heat energy required to raise the temperature of 1 kg of a substance by 1 Kelvin.
- Water has a high specific heat, enabling it to regulate temperature slowly.
Latent Heat of Vaporization: Energy required to change a substance from liquid to gas without changing temperature.
Heat Transfer Mechanisms:
- Conduction: Heat transfer through direct contact (solids).
- Convection: Heat transfer through fluid movement (liquids and gases).
- Radiation