Weak Interactions in Aqueous Systems, Acids, Bases, pH, and Biochemical Calculations

Vocabulary flashcards covering weak interactions, molecular polarity, ionization of water, pH scale, buffers, and concentration calculations based on the lecture material.

Bond energy (E)

The amount of energy required to break apart a mole of molecules into its component atoms.

Electronegativity

The tendency for an atom of a given chemical element to attract shared electrons (or electron density) when forming a chemical bond.

Polar molecule

A molecule in which one end of the molecule is slightly positive, while the other end is slightly negative.

Van der Waals interactions

Weak intermolecular attractions driven by induced electrical interactions between two or more atoms or molecules that are very close to each other.

Hydrogen bond

An interaction between a hydrogen atom covalently bonded to another atom and a pair of nonbonded electrons on a separate atom (most often oxygen or nitrogen in biomolecules).

Hydrogen-bond donor

The atom to which the hydrogen atom involved in a hydrogen bond is covalently bonded.

Hydrogen-bond acceptor

The atom containing the nonbonded electron pair involved in a hydrogen bond.

Hydrophilic

Describing compounds that dissolve easily in water ("water-loving"), which are generally charged or polar compounds.

Hydrophobicity

The physical property of a molecule that is seemingly repelled from a mass of water.

Amphipathic molecule

A molecule that has a strongly hydrophilic "head" group coupled to a hydrophobic "tail" (usually a hydrocarbon).

Brønsted-Lowry Acid

A chemical species that can donate a proton.

Brønsted-Lowry Base

A chemical species that can accept a proton.

Strong acid

An acid that dissociates almost completely into a proton and a weak conjugate base in solution.

Amphiprotic species

Molecules or ions that can either donate or accept a proton, depending on their circumstances.

Ion product of water ($K_\text{w}$)

The equilibrium constant for the ionization of water, defined as $K_\text{w} = [\text{H}^+][\text{OH}^-]$, which equals $1 \times 10^{-14}\,\text{M}^2$ at $25\,^\circ\text{C}$.

pH

The negative logarithm to the base 10 of the hydrogen ion concentration, expressed as $\text{pH} = -\log[\text{H}^+]$.

Physiological pH range

The normal pH range of most body fluids, typically between $6.5$ and $8.0$ (with arterial blood range strictly maintained between $7.35$ and $7.45$).

Acid dissociation constant ($K_\text{a}$)

The equilibrium constant for the dissociation of a weak acid $\text{HA}$, expressed as $K_\text{a} = \frac{[\text{H}^+][\text{A}^-]}{[\text{HA}]}$.

$$\text{p}K_\text{a}$$

The negative logarithm of the acid dissociation constant ($-\log K_\text{a}$), where a numerically smaller value corresponds to a stronger acid.

Henderson–Hasselbalch Equation

An equation expressing pH in terms of $\text{p}K_\text{a}$ and base/acid ratio: $\text{pH} = \text{p}K_\text{a} + \log\left(\frac{[\text{A}^-]}{[\text{HA}]}\right)$.

Titration

A procedure used to determine the concentration of an acid in solution by incrementally adding a measured volume of strong base of known concentration until neutralization.

Buffer solution

A solution that resists changes in pH when small amounts of acid or base are added, typically consisting of a mixture of a weak acid and a salt of its conjugate base.

Solute

The substance being dissolved in a liquid solvent.

Solvent

The liquid in which a solute is dissolved to form a solution.

Molarity (M)

A unit of concentration defined as the number of moles of solute dissolved per liter of solution ($\text{mol/L}$).

Normality (N)

A concentration term expressing the number of equivalents of solute per liter of solution.

Molality (m)

The total moles of a solute contained in one kilogram of a solvent.

Osmolarity

The molarity of particles in a solution, calculated as $n \times M$ for dissociable substances, where $n$ is the number of ions produced per molecule.

Dilution

The process of decreasing the concentration of a solute in a solution, usually by mixing with additional solvent.

Serial dilution

A step-by-step series of simple dilutions where the source material for each step originates from the diluted solution of the preceding step.