Acids, Bases, and Buffers Lecture Notes

Practice flashcards covering definitions and concepts of acids, bases, pH, titrations, and buffer solutions based on the provided lecture transcript.

Brønsted-Lowry acid

A substance that can donate a proton ($H^+$ ion).

Brønsted-Lowry base

A substance that can accept a proton ($H^+$ ion).

Alkali

A water-soluble base that produces $OH^-$ ions in aqueous solution.

Oxonium ion

The ion $H_3O^+$ (also called hydronium or hydroxonium) formed when a proton bonds with a water molecule in aqueous solution.

Ionic product of water ($K_w$)

The equilibrium constant for the ionisation of water, expressed as $K_w = [H^+(aq)][OH^-(aq)]$, which equals $1.0 \times 10^{-14}\text{ mol}^2\text{ dm}^{-6}$ at $298\text{ K}$.

pH

A logarithmic scale of acidity defined as $pH = -\log_{10}[H^+(aq)]$.

Strong acid

An acid, such as hydrochloric acid ($HCl$), that dissociates completely into ions in aqueous solution.

Strong base

A base, such as sodium hydroxide ($NaOH$), that is fully dissociated into ions in aqueous solution.

Weak acid

An acid, such as ethanoic acid ($CH_3COOH$), that is only slightly ionised or not fully dissociated when dissolved in water.

Weak base

A base, such as ammonia ($NH_3$), that reacts with water in an equilibrium that lies well to the left, producing few $OH^-$ ions.

Acid dissociation constant ($K_a$)

The equilibrium constant for the dissociation of a weak acid, given by $K_a = \frac{[H^+(aq)]_{eqm}[A^-(aq)]_{eqm}}{[HA(aq)]_{eqm}}$ with units in $\text{mol dm}^{-3}$.

$$pK_a$$

A logarithmic measure of acid strength defined as $pK_a = -\log_{10} K_a$; the smaller the value, the stronger the weak acid.

Equivalence point

The point in a titration where sufficient base has been added to just neutralise the acid (or vice-versa); also known as the stoichiometric point.

End point

The volume of alkali or acid added in a titration when the indicator just changes colour.

Monoprotic acid

An acid that has only one acidic hydrogen that can be donated to a base, such as $HCl$.

Diprotic acid

An acid that has two acidic hydrogens that can be donated to a base, such as $H_2SO_4$.

Buffer solution

A solution that resists changes in pH when small amounts of acid or alkali are added to it.

Acidic buffer

A mixture of a weak acid and its soluble salt that maintains a pH below 7.

Basic buffer

A mixture of a weak base and its soluble salt that maintains a pH above 7.

Half-neutralisation point

The point halfway between zero and the equivalence point in a titration where $[HA] = [A^-]$ and $pH = pK_a$.

Henderson-Hasselbalch equation

A logarithmic form of the acid dissociation constant expression used to calculate the pH of a buffer: $pH = pK_a - \log_{10} \frac{[HA]}{[A^-]}$.