Glossary
Analyte
The solution with the unknown concentration whose quantity or concentration is being determined in a titration.
Example:
In a titration to find the concentration of HCl, the HCl solution is the analyte.
Buffer
A solution containing a weak acid and its conjugate base (or a weak base and its conjugate acid) that resists significant changes in pH upon the addition of small amounts of acid or base.
Example:
In a weak acid titration, a buffer region forms before the equivalence point, where the pH changes slowly.
Burette
A graduated glass tube with a stopcock at the bottom, used to deliver precise, variable volumes of liquid, especially in titrations.
Example:
A chemist carefully reads the volume of NaOH dispensed from the burette during an acid-base titration.
Equivalence Point
The point in a titration where the moles of titrant added exactly equal the moles of analyte initially present, indicating the completion of the reaction.
Example:
For a strong acid-strong base titration, the equivalence point is reached when the pH of the solution becomes 7.0.
Half-equivalence point
The point in a weak acid-strong base or weak base-strong acid titration where exactly half of the initial weak acid or base has been neutralized.
Example:
At the half-equivalence point of a weak acid titration, the pH of the solution is equal to the pKa of the weak acid.
Henderson-Hasselbalch equation
An equation that relates the pH (or pOH) of a buffer solution to the pKa (or pKb) of the weak acid (or base) and the ratio of the concentrations of the conjugate acid-base pair.
Example:
The Henderson-Hasselbalch equation is invaluable for calculating the pH of a buffer solution at any point before the equivalence point in a weak acid/base titration.
Meniscus
The curved surface of a liquid in a tube, typically concave for water-based solutions due to adhesion.
Example:
When reading a burette, one must always read the volume from the bottom of the meniscus for accuracy.
Post-Equivalence Point
The region of a titration curve after the equivalence point, where the titrant is in excess.
Example:
The pH in the post-equivalence point region is primarily determined by the excess strong acid or base added.
Pre-Equivalence Point
The region of a titration curve before the equivalence point is reached, where the analyte is in excess.
Example:
In the pre-equivalence point region of a weak acid titration, a buffer solution is formed.
Strong Acid - Strong Base Titration
A titration involving the reaction between a strong acid and a strong base, characterized by a sharp pH change around the equivalence point at pH 7.
Example:
The titration of HCl with NaOH is a classic example of a strong acid - strong base titration.
Titrant
The solution of known concentration that is added incrementally from a burette during a titration.
Example:
When standardizing an acid, a precisely measured solution of NaOH acts as the titrant.
Titration
A laboratory technique used to determine the unknown concentration of a solution by reacting it with a solution of known concentration.
Example:
Performing a titration to find out how much acetic acid is in a bottle of vinegar.
Titration Curve
A graph that plots the pH of a solution against the volume of titrant added during a titration.
Example:
Analyzing the shape of a titration curve can reveal whether the acid or base involved is strong or weak.
Weak Acid Titration
A titration where a weak acid is reacted with a strong base, resulting in a buffer region before the equivalence point and an equivalence point pH greater than 7.
Example:
Titrating acetic acid with sodium hydroxide is an example of a weak acid titration.
Weak Base Titration
A titration where a weak base is reacted with a strong acid, resulting in a buffer region before the equivalence point and an equivalence point pH less than 7.
Example:
Titrating ammonia with hydrochloric acid is an example of a weak base titration.
nMaVa = mMbVb
An equation used at the equivalence point of a titration to relate the molarities and volumes of the acid and base, incorporating their stoichiometric coefficients.
Example:
To find the unknown concentration of an acid, you can use nMaVa = mMbVb after determining the volume of base needed to reach the equivalence point.