Glossary
Acid-Base Titrations
A specific type of titration used to determine the concentration of an acid or a base by neutralizing it with a solution of known concentration of the opposite type.
Example:
A common acid-base titration involves using a strong base like NaOH to find the concentration of a weak acid like acetic acid in vinegar.
Amphiprotic Water
Water's ability to act as both a Brønsted-Lowry acid (donating a proton) and a Brønsted-Lowry base (accepting a proton).
Example:
In the autoionization of water, one water molecule acts as an acid and another as a base, demonstrating amphiprotic water behavior.
Analyte
The solution with an unknown concentration that is being analyzed in a titration, typically placed in an Erlenmeyer flask.
Example:
To determine the concentration of an unknown HCl solution, the HCl is the analyte being tested.
Brønsted-Lowry Acid
A species that donates a proton (H⁺) in a chemical reaction.
Example:
In the reaction HCl + H₂O → H₃O⁺ + Cl⁻, HCl acts as a Brønsted-Lowry acid by donating a proton to water.
Brønsted-Lowry Base
A species that accepts a proton (H⁺) in a chemical reaction.
Example:
When ammonia (NH₃) reacts with water to form NH₄⁺ and OH⁻, NH₃ is the Brønsted-Lowry base because it accepts a proton from water.
Complexation Titrations
Titrations based on the formation of a soluble complex compound between the titrant and the analyte, often used to determine metal ion concentrations.
Example:
An EDTA complexation titration is frequently used to measure the hardness of water by quantifying the calcium and magnesium ions present.
Conjugate Acid
The species formed when a Brønsted-Lowry base accepts a proton.
Example:
When the acetate ion (CH₃COO⁻) accepts a proton, it forms its conjugate acid, acetic acid (CH₃COOH).
Conjugate Base
The species formed when a Brønsted-Lowry acid donates a proton.
Example:
After carbonic acid (H₂CO₃) donates a proton, it becomes its conjugate base, the bicarbonate ion (HCO₃⁻).
Endpoint
The experimental point in a titration where the indicator changes color, signaling that the reaction is perceived to be complete.
Example:
You stop adding titrant when you observe the endpoint, which is when the indicator's color change persists for at least 30 seconds.
Equivalence Point
The theoretical point in a titration where the moles of titrant added exactly equal the moles of analyte initially present, signifying the completion of the reaction.
Example:
At the equivalence point of a strong acid-strong base titration, the pH will be exactly 7, as all the acid and base have neutralized each other.
Indicator
A substance, typically a weak acid or base, that changes color within a specific pH range, signaling the endpoint of a titration.
Example:
In an acid-base titration, adding phenolphthalein as an indicator will cause the solution to turn pink when the endpoint is reached.
Inflection Point
The point on a titration curve where the slope changes dramatically, corresponding to the equivalence point.
Example:
The steepest part of the S-shaped curve on a titration graph marks the inflection point, which is where the moles of acid and base are equal.
Linear Region
The portion of a titration curve where the pH changes gradually, often indicating a buffer region in weak acid/base titrations.
Example:
In the linear region of a weak acid-strong base titration curve, the solution resists large pH changes due to the presence of a conjugate acid-base pair.
M_aV_a = M_bV_b
A simplified equation used for titration calculations at the equivalence point, where the moles of acid equal the moles of base, assuming a 1:1 mole ratio.
Example:
If you know the molarity and volume of a strong acid, you can use M_aV_a = M_bV_b to quickly calculate the unknown molarity of a strong base required for neutralization.
Precipitation Titrations
Titrations where the reaction between the titrant and analyte forms an insoluble precipitate, used to determine the concentration of a substance that forms a precipitate.
Example:
Determining the chloride ion concentration in water can be done via a precipitation titration using silver nitrate, where the formation of silver chloride indicates the reaction's completion.
Redox Titrations
Titrations that involve an oxidation-reduction reaction, used to determine the concentration of an oxidizing or reducing agent.
Example:
A redox titration might use potassium permanganate to determine the concentration of iron(II) ions in a sample, with the endpoint often indicated by a distinct color change.
Titrant
The solution of known concentration that is added from a burette during a titration.
Example:
When titrating an unknown acid, a precisely measured 0.100 M NaOH solution acts as the titrant.
Titration Curve
A graph that plots the pH of the analyte solution against the volume of titrant added, visually representing the pH changes throughout a titration.
Example:
Analyzing the shape of a titration curve can help determine if the acid or base involved is strong or weak.
Titrations
A quantitative chemical analysis method used to determine the unknown concentration of a reactant by reacting it with a solution of known concentration.
Example:
In a lab, you might perform a titration to find out how much acetic acid is really in that bottle of vinegar.