Chapter 3 | Water and Life

Hydrogen Bonds

Weak bonds that form between the partial positive charge of a hydrogen atom in one molecule and the partial negative charge of an oxygen atom in another molecule

Polarity of Water

Water molecules have a partial negative charge around the oxygen atom and partial positive charges around the hydrogen atoms. This polarity allows water molecules to form hydrogen bonds with each other

Cohesion

The tendency of water molecules to stick to each other due to hydrogen bonding. This property allows water to form droplets and maintain surface tension

Adhesion

The tendency of water molecules to stick to other substances, especially those that are hydrophilic (polar molecules). This property is responsible for water’s ability to climb up plant stems through capillary action

High Surface Tension

The strong cohesive forces between water molecules at the surface, which makes it difficult to break through the surface layer. This is why water striders can walk on water and why water droplets retain their shape

High Specific Heat

The amount of heat required to raise the temperature of a substance by one degree Celsius. Water has a high specific heat, meaning it absorbs and releases heat more slowly than many other substances

Evaporative Cooling

The process by which the evaporation of water removes heat from the surface, cooling the surrounding area (e.g., sweating)

Ice Floats

When water freezes, its molecules form a crystalline structure with more empty space, making it less dense than liquid water

Solution

A homogenous mixture of two or more substances

Solvent

The substance that dissolves other substances (in most cases, this is water)

Solute

The substance that is dissolved in the solvent

Hydrophilic

Substances that are attracted to water and can dissolve in it (e.g., salts, sugars)

Hydrophobic

Substances that repel water and do not dissolve in it (e.g., oils)

Acid

A substance that increases the concentration of hydrogen ions (H⁺) in a solution, resulting in a pH less than 7. Example: Hydrochloric acid (HCl) dissociates into H⁺ and Cl⁻

Base

A substance that decreases the concentration of hydrogen ions (H⁺) in a solution, resulting in a pH greater than 7. Example: Sodium hydroxide (NaOH) dissociates into Na⁺ and OH⁻

Hydronium Ion (H₃O⁺)

Formed when a hydrogen ion (H⁺) associates with a water molecule

Hydroxide Ion (OH⁻)

Formed when a base dissociates in water

pH Scale

A scale used to measure the acidity or basicity of a solution. It ranges from 0 (acidic) to 14 (basic), with 7 being neutral