Glossary
Acids
Substances that increase the concentration of hydrogen ions (H⁺) in a solution, typically by donating H⁺.
Example:
Lemon juice is an acid because it releases H⁺ ions, giving it a sour taste and a low pH.
Adhesion
The property of water where water molecules are attracted to and stick to other polar or charged surfaces.
Example:
Water droplets clinging to the side of a glass after you've emptied it demonstrate adhesion.
Bases
Substances that decrease the concentration of hydrogen ions (H⁺) in a solution, typically by accepting H⁺ or releasing hydroxide ions (OH⁻).
Example:
Baking soda is a base that can neutralize acids, often used to relieve heartburn.
Cohesion
The property of water where water molecules are attracted to and stick to other water molecules, primarily due to hydrogen bonding.
Example:
The continuous column of water moving up a tall tree is maintained by cohesion among water molecules.
Dissociation of Water
The reversible process where water molecules break apart into hydrogen ions (H⁺, often as H₃O⁺) and hydroxide ions (OH⁻).
Example:
The dissociation of water is fundamental to understanding pH, as it determines the concentration of H⁺ and OH⁻ ions in a solution.
Evaporative Cooling
The process by which a liquid cools a surface as it evaporates, absorbing a significant amount of heat energy from the surface.
Example:
When you sweat during exercise, the evaporative cooling of the sweat helps lower your body temperature.
Hydrogen Bond
A weak intermolecular attraction formed between a partially positive hydrogen atom (bonded to an electronegative atom) and another partially negative electronegative atom.
Example:
The double helix structure of DNA is stabilized by numerous hydrogen bonds between complementary base pairs.
Hydrophilic
Describes substances that have an affinity for water and are attracted to it, often due to their polar or ionic nature.
Example:
Sugar is hydrophilic, which is why it dissolves so easily in your tea.
Hydrophobic
Describes substances that avoid water and are not attracted to it, typically because they are nonpolar.
Example:
The oily residue on a pan is hydrophobic, causing water to bead up on its surface rather than mixing.
Logarithmic Scale
A scale where each unit represents a tenfold change in the quantity being measured.
Example:
Because the pH scale is a logarithmic scale, a solution with a pH of 4 is ten times more acidic than a solution with a pH of 5.
Neutral pH
A pH value of 7.0, indicating an equal concentration of hydrogen ions (H⁺) and hydroxide ions (OH⁻) in a solution.
Example:
Pure distilled water has a neutral pH of 7.0.
Polar Molecule
A molecule with an unequal distribution of charge, resulting in distinct partial positive and partial negative regions.
Example:
Water is a polar molecule because oxygen pulls electrons more strongly than hydrogen, creating a slight negative charge on oxygen and slight positive charges on hydrogens.
Specific Heat
The amount of heat energy required to raise the temperature of one gram of a substance by one degree Celsius.
Example:
Water's high specific heat helps regulate Earth's climate, as oceans absorb and release large amounts of heat with minimal temperature fluctuations.
Surface Tension
A property of water caused by the stronger attractive forces (cohesion) between water molecules at the surface compared to those below, creating a 'skin' effect.
Example:
A small insect can walk on water without sinking due to the high surface tension of the water.
pH Scale
A logarithmic scale ranging from 0 to 14 that measures the acidity or alkalinity of a solution based on its hydrogen ion concentration.
Example:
A chemist uses the pH scale to determine if a newly synthesized compound is acidic, basic, or neutral.