Determination of Ka and Identification of an Unknown Weak Acid

This set of vocabulary flashcards covers the fundamental concepts of Bronsted-Lowry acid-base theory, the properties of strong and weak acids, and the technical terminology associated with acid-base titrations and dissociation constants.

Bronsted-Lowry acid

A substance which will donate a proton ($H^+$ ion) in aqueous solution to another substance.

Bronsted-Lowry base

A substance which is capable of accepting a proton from another substance in aqueous solution.

Monoprotic acids

Acids that have only one ionizable, or transferable, hydrogen ion (proton), such as hydrochloric acid ($HCl$), nitric acid ($HNO_3$), and acetic acid ($HC_2H_3O_2$).

Diprotic acids

Acids that have two ionizable hydrogen ions per molecule of acid, including sulfuric acid ($H_2SO_4$) and oxalic acid ($H_2C_2O_4$).

Strong acid

An acid which dissociates completely into its constituent ions in aqueous solution.

Weak acid

An acid which only partially ionizes into ions in aqueous solution.

Six Strong Acids

Hydrochloric acid ($HCl$), nitric acid ($HNO_3$), hydrobromic acid ($HBr$), perchloric acid ($HClO_4$), hydroiodic acid ($HI$), and sulfuric acid ($H_2SO_4$).

$$K_{a}$$

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

$$pK_{a}$$

A value used to compare acid strengths calculated by the equation $pK_{a} = -\text{log}(K_{a})$.

Titration

An experimental procedure in which a standardized solution is carefully added to a solution whose concentration is imprecisely known.

Titrant

A standardized solution whose concentration is very precisely known.

Equivalence point

The point at which the acid and base have exactly neutralized one another and the number of moles of $H^+$ equals the number of moles of $OH^-$ added.

Endpoint

The point in a titration at which an acid-base indicator, such as phenolphthalein, gives a color change signaling neutralization.

Titration curve

A graph constructed by plotting pH on the y-axis versus volume of $NaOH$ on the x-axis.

First derivative plot

A mathematical graph of the derivative of pH versus volume of $NaOH$ where the equivalence point is identified as the maximum slope (the peak).

Half-equivalence point

The point in a titration where exactly half the acid has been converted into its conjugate base ($[HA] = [A^-]$), and the measured $pH = pK_{a}$.

Molar mass of acid

The value calculated by dividing the mass of acid in grams by the number of moles of acid neutralized, expressed in $g/mol$.