🧪 5A [Reactions in Aqueous Solutions]

Water Dissociation Constant

An expression of the autoionization of water into H⁺ and OH⁻ at a certain temperature, given by the product of the ions' molar concentrations.

Denoted by K_w, and equal to 10⁻¹⁴ at 25°C. K_w = [H⁺][OH⁻].

Titration

An analytical procedure in which a solution of known concentration is slowly added to a solution of unknown concentration to the point of molar equivalency, thereby providing the concentration of the unknown solution.

Titrant

A solution of known concentration added in small volumes to a solution of unknown concentration to reach the equivalence point.

Titrand

A solution of unknown concentration to which small volumes of a solution of known concentration are added to reach the equivalence point.

Strong Acid

An acid that will completely dissociate in aqueous solution (such as HCl, HI, HNO₃, and HClO₄).

Solvent

A medium, commonly a liquid, into which a solute is dissolved to create a solution.

Solvation

The process of forming a cagelike network of solvent molecules around a solute in a solution.

Solution Equilibrium

When a solute is dissolved in a solvent, it will dissociate until reaching an equilibrium point at which the rate of dissociation equals the rate of precipitation of the solute, regardless of any additional solute introduced into the mixture.v

Solute

A compound, commonly an ion, dissolved in a solvent to create a solution.

Solubility Product Constant

The product of the molar concentrations of dissociated ions in a saturated solution, where each ion is raised to the power of its stoichiometric coefficient. Denoted Kₛₚ.

Solubility

A ratio that measures how much solute can dissolve in a solvent at a given temperature.

Raoult's Law

States that the vapor pressure of a solvent is proportional to the mole fraction of the solvent in the solution; provides an explanation for the boiling point elevation seen in solutions.

pH

Scaled value used to measure the acidic strength of a solution, calculated by taking the negative logarithm of the proton concentration in a solution:

pH = -log [H⁺].

Normality

Concentration of a solution calculated by gram equivalent weight of solute per liter of solution, often denoted by N.

Neutralization Reaction

A reaction in which an acid and a base are combined to form a salt (and often water as well).

Molarity

Concentration of a solution calculated by moles of solute per liters of solution, often denoted by M.

Molar Solubility

The molarity of a solute such that a solution is saturated (at equilibrium).

Molality

Concentration of a solution calculated by moles of solute per kilograms of solvent, often denoted by m.

Lewis Definition

A definition of acids as electron pair acceptors and bases as electron pair donors.

Ion Product

The product of the molar concentrations of dissociated ions in solution at any point in a dissociation reaction, where each ion is raised to the power of its stoichiometric coefficient. Denoted IP.

Indicator

A chemical species that changes color when undergoing dissociation. Indicators are used to signal the end point of a titration.

Henderson-Hasselbalch Equation

An equation commonly used in titrationbased problems that relates the pH or pOH of a solution to the pKₐ and the ratio of the dissociated species. 

pH=pKa+log (A^-/HA).

Half-Equivalence Point

The point in a titration at which exactly half the molar equivalence of reactant is consumed by the titrant being added. At this point in an acid-base titration, the pH is equal to the pKₐ of the titrand.

Equivalence Point

The point in a titration at which an equimolar amount of titrant has been added to the unknown solution.

Conjugate Acids and Bases

A systematic pairing of a protonated species (acid) with its deprotonated form (conjugate base) or a deprotonated species (base) with its protonated form (conjugate acid). Conjugates appear on opposite sides of a chemical equation.

Concentration

The ratio of the amount of solute to the amount of solution; quantified by mole fraction, molarity, molality, or normality, among other measures.

Common Ion Effect

States that the molar solubility of one salt is reduced when another salt, having a common ion, is brought into the same solution.

Colligative Properties

The properties of solutions—such as vapor pressure lowering, freezing point depression, boiling point elevation, and osmotic pressure—that are affected only by the number of solute particles dissolved and not by their chemical identities.

Buffer

A solution containing a weak acid or base coupled with its conjugate salt, acting to prevent changes to the solution's pH upon the addition of acidic or basic substances.

Brønsted-Lowry Definition

Common definition of acids as proton (H⁺) donors and bases as proton acceptors.

Arrhenius Definition

A definition of acids as producers of excess H⁺ and bases as producers of excess OH⁻ in aqueous solutions.

Aqueous Solution

A solution containing water as its solvent.

Amphoteric

A species capable of reacting as either an acid or a base. In the Brønsted-Lowry sense, a species that can pick up or give off a proton. In the Lewis sense, a species that can donate or accept a lone pair of electrons.

Acid Dissociation Constant

An equilibrium expression used to measure acid strength, given by the ratio of the product of the products' molar concentrations to the product of the reactants' molar concentrations, with each term raised to the power of its stoichiometric coefficient. Denoted Kₐ.

Logarithm

A mathematical function that is the inverse of the exponentiation function. Logarithms with base ten are called common logarithms (log); logarithms with Euler's number (e ≈ 2.72) are called natural logarithms (ln).