Glossary
Acid Excess
A region in a titration where the initial acid is present in a greater amount than the added base, resulting in an acidic solution.
Example:
Before the equivalence point in a strong acid-strong base titration, the solution is in acid excess, and its pH is low.
Acid Only (region)
The initial phase of a titration where only the acid (either strong or weak) is present before any base has been added.
Example:
Before starting the titration, the beaker contains only the initial acid, representing the acid only region.
Base Excess
A region in a titration where the added base is present in a greater amount than the initial acid, resulting in a basic solution.
Example:
After the equivalence point in a strong acid-strong base titration, the solution is in base excess, leading to a high pH.
Buffer Region
The portion of a titration curve for a weak acid/strong base (or vice versa) where significant amounts of both the weak acid and its conjugate base are present, resisting pH changes.
Example:
The relatively flat part of a weak acid titration curve is the buffer region, where the solution effectively resists pH changes.
Buffers
Mixtures of a weak acid and its conjugate base that resist significant changes in pH when small amounts of acid or base are added.
Example:
Your blood is a buffer system, maintaining a stable pH around 7.4, crucial for enzyme function and overall health.
Conjugate Acid/Base Pairs
Two species that differ by the presence or absence of a proton (H+). The acid has one more proton than its conjugate base.
Example:
Ammonia (NH3) and ammonium ion (NH4+) form a conjugate acid/base pair, with NH4+ being the acid and NH3 its conjugate base.
Conjugate Base (A-)
The species formed after a weak acid donates its proton. It is capable of accepting a proton to reform the acid.
Example:
When hydrofluoric acid (HF) loses a proton, it forms the fluoride ion (F-), which is its conjugate base.
Equimolar
A state where the moles of two reacting substances are equal, often referring to the equivalence point in a titration.
Example:
At the equivalence point of a titration, the acid and base are equimolar, meaning they have reacted completely in their stoichiometric ratio.
Equivalence Point
The point in a titration where the moles of titrant added are stoichiometrically equal to the moles of the substance being titrated.
Example:
At the equivalence point of a strong acid-strong base titration, the pH is 7, indicating complete neutralization.
Half-equivalence Point
The point in a weak acid-strong base titration where exactly half of the initial weak acid has been neutralized, and pH = pKa.
Example:
At the half-equivalence point, the concentrations of the weak acid and its conjugate base are equal, simplifying pH calculations.
Henderson-Hasselbalch Equation
An equation used to calculate the pH of a buffer solution, relating pH to the pKa of the weak acid and the ratio of the concentrations of the conjugate base and weak acid.
Example:
To determine the pH of a buffer made from acetic acid and acetate, you would use the Henderson-Hasselbalch equation.
Homeostasis
The ability of an organism or system to maintain internal stability, often involving the regulation of pH, temperature, and other conditions.
Example:
Maintaining a stable body temperature is an example of homeostasis in biological systems, just as buffers maintain pH.
ICE Table
A tabular method (Initial, Change, Equilibrium) used to organize and calculate equilibrium concentrations of reactants and products in a reversible reaction.
Example:
To find the pH of a weak acid solution, you often set up an ICE table to determine the equilibrium concentration of H+.
Ka
The acid dissociation constant, an equilibrium constant that quantifies the extent to which a weak acid dissociates in solution.
Example:
A larger Ka value indicates a stronger weak acid, meaning it dissociates more readily.
Kb
The base dissociation constant, an equilibrium constant that quantifies the extent to which a weak base dissociates in solution.
Example:
A high Kb value signifies a stronger weak base, which produces more hydroxide ions in water.
Kw
The ion-product constant for water, representing the equilibrium constant for the autoionization of water (H2O <=> H+ + OH-), which is 1.0 x 10^-14 at 25°C.
Example:
The relationship between Ka and Kb for a conjugate acid-base pair is given by Ka * Kb = Kw.
Net Ionic Equation
An equation that shows only the species that participate directly in a chemical reaction, excluding spectator ions.
Example:
For the reaction of HCl and NaOH, the net ionic equation is H+(aq) + OH-(aq) → H2O(l), highlighting the formation of water.
Post-equivalence Region
The portion of a titration curve after the equivalence point, where the titrant (either acid or base) is in excess.
Example:
Beyond the equivalence point, the solution enters the post-equivalence region, and the pH is primarily determined by the excess titrant.
Spectator Ions
Ions that are present in a solution during a chemical reaction but do not participate in the reaction itself.
Example:
In the reaction between NaCl and AgNO3, the Na+ and NO3- ions are spectator ions because they remain in solution unchanged.
Stoichiometry
The quantitative relationship between reactants and products in a chemical reaction, based on mole ratios from the balanced equation.
Example:
Using stoichiometry, you can calculate how many grams of product will form from a given amount of reactant.
Strong Acid - Strong Base Reactions
Reactions between a strong acid and a strong base that proceed to completion, typically forming a neutral salt and water.
Example:
The neutralization of hydrochloric acid (HCl) with sodium hydroxide (NaOH) is a classic strong acid - strong base reaction.
Weak Acid (HA)
An acid that only partially dissociates in water, meaning it does not donate all of its protons.
Example:
Acetic acid (CH3COOH), found in vinegar, is a common weak acid used in buffer solutions.
Weak Acid - Strong Base Reactions
Reactions involving a weak acid and a strong base, which typically result in the formation of a buffer solution before the equivalence point.
Example:
Titrating formic acid (a weak acid) with potassium hydroxide (a strong base) is an example of a weak acid - strong base reaction.
pH
A measure of the hydrogen ion concentration in a solution, indicating its acidity or alkalinity.
Example:
A solution with a pH of 2 is highly acidic, while a solution with a pH of 12 is highly basic.
pKa
The negative logarithm (base 10) of the acid dissociation constant (Ka), indicating the strength of a weak acid.
Example:
A weak acid with a pKa of 4.74 is stronger than one with a pKa of 9.25.
pOH
A measure of the hydroxide ion concentration in a solution, related to pH by the equation pH + pOH = 14 at 25°C.
Example:
If a solution has a high concentration of OH- ions, its pOH will be low, indicating a basic solution.