Lecture 1: Water, Acids, Bases, and Buffers

Vocabulary practice flashcards covering water properties, noncovalent bonds, acids, bases, pH, and buffering systems.

Electronegativity

An atom's attraction to electrons in a bond, with Fluorine having the highest electronegativity value of $4.0$.

Hydrophilic

Describing substances that are soluble in water, which are usually polar molecules.

Hydrophobic

Describing substances that are not soluble in water, which are non-polar molecules.

Amphipathic

Describing a molecule that contains both hydrophilic and hydrophobic regions, such as a phospholipid.

Micelle

A spherical structure formed by amphipathic molecules in water with a hydrophobic interior and a hydrophilic exterior.

Bilayer

A structure composed of two layers of lipids with hydrophobic regions hidden in-between and hydrophilic regions on the outside.

Liposome

A spherical bilayer with hydrophilic regions in both the interior and exterior, and hydrophobic regions hidden in-between the two layers.

Hydrogen bond

A weak noncovalent bond involving a hydrogen bond donor and an electronegative acceptor atom like nitrogen or oxygen, with an energy of $8\text{ to }20\,\text{kJ\,mol}^{-1}$.

Hydrophobic effect

The passive clustering of nonpolar groups to avoid water, which minimizes the loss of hydrogen bonds between water molecules without requiring energy input.

Van der Waals interactions

Nonspecific interactions between any two atoms coming within $3\text{ to }4\,\text{\AA}$ of each other, driven by transient electrostatic charges.

Acid

A proton ($\text{H}^+$) donor.

Base

A proton ($\text{H}^+$) acceptor.

Strong acid

An acid that completely ionizes in aqueous solution, such as $\text{HCl}$ or $\text{H}_2\text{SO}_4$.

Weak acid

An acid that incompletely ionizes in aqueous solution, such as $\text{CH}_3\text{COOH}$ or $\text{H}_2\text{CO}_3$.

Ion product of water ($K_w$)

The product of hydrogen and hydroxide ion concentrations, $K_w = [\text{H}^+][\text{OH}^-] = 10^{-14}\,\text{M}^2$ at $25\,^\circ\text{C}$.

pH

An indicator of hydrogen ion concentration, defined mathematically as $\text{pH} = -\log_{10}[\text{H}^+]$.

$$\text{p}K_a$$

The logarithmic scale value defined as $\text{p}K_a = -\log_{10}(K_a)$, representing the pH at which an acid and its conjugate base are equal in concentration.

Titration

A process in which an acid is neutralized by an increasing amount of base or vice versa.

Buffer

A solution of a weak acid or base whose pH resists change when a small amount of base or acid is added.

Equivalence point

The ideal point in a titration where all of the starting base or acid is completely neutralized.

Buffer capacity

The ability of a buffer to resist pH change, which increases with higher concentration and is highest at a pH close to its $\text{p}K_a$.