Chapter 2.5: The Properties of Water Are Critical to the Chemistry of Life

Flashcards from Chapter 2.5 of Principles of Life, 3rd Edition.

Specific heat

The amount of heat needed to raise 1 gram of water by 1 degree Celsius

• This is naturally high in water and enables its existence in many organisms, buffering temperature

Heat of vaporization

The amount of energy needed for vaporization

• This is naturally high in water and enables the cooling of living organisms due to its absorption

Density

The ratio of a substance’s mass to volume

• This is lower in ice compared to water due to greater organization, which enables lakes to freeze top to bottom

Hydrogen bonds

Bonds between hydrogen atoms of different molecules; these can create cohesion (which holds water together for surface tension) and adhesion (which allows water to adhere to another surface)

Solvent

What dissolves a specific substance; these change distributions but do not break molecular structures

• Water is a type of this, forming weak attractions with substances with polarity, thus dividing hydrophilic and hydrophobic reactions

Hydrophilic

The tendency to be attracted to and dissolve in water; this is greater in polar molecules due to the creation of a hydration shell surrounding both ions

• The sum of these forces against a bond’s strength determines dissolution

• Common in biology

Hydrophobic

The tendency to not be attracted to and dissolve in water; this is seen in non-polar substances such as oil which do not form hydration shells

Amphipathic

Substances that are both hydrophilic and hydrophobic

Self-ionization

When H₂O spontaneously ionizes into H₃O⁺ and OH^-

• Occurs in very small amounts

Neutral solution

A solution in which the concentration of H⁺ (hydronium) ions is equal to the concentration of OH^- (hydroxide) ions

Acids

These raise H⁺ concentrations relative to OH^-

• Can be strong or weak depending on substance’s resistance to allowing a free H+

Bases

These produce more OH^- against H⁺ when as a result of dissociation, forming water with some of the H⁺ ions

• Can be strong or weak depending on stability; OH- is just very unstable and easily absorbs an H+

Buffer

A solution that reduces the impact of acids or bases on pH relative to if they were not present at all

• Acids adding H⁺ react with a negative ion in a buffer to form the original reactant, reducing the acid’s impact

• Bases adding OH^- react with the H⁺ in a buffer to form water, reducing basic impact

• Required in living systems, seen in blood to have a constant pH

pH

The negative log of the concentration of H₃O ions

• Neutral substances have concentrations of 10^-7 H₃O M

• Acidic substances have concentrations greater than 10^-7 H₃O M, resulting in a lower number

• Basic substances have concentrations less than 10^-7 H₃O M, resulting in a greater number