pH and Buffers Flashcards

Vocabulary flashcards for key terms related to pH, buffers, acids, and bases.

Buffer

A solution which resists a change in pH when either acid or base is added to it.

pH Scale

Measures how acidic or basic a substance is, ranging from 0 to 14.

Acidic Solution (pH)

A solution with a pH less than 7.

Basic Solution (pH)

A solution with a pH greater than 7; also known as alkaline.

Neutral pH

A pH of 7, such as that of pure water, where the number of H+ ions equals the number of OH- ions.

pH Determination Methods

Includes pH indicator paper/strips, indicator dyes (e.g., litmus, phenolphthalein, phenol red), and glass electrodes (pH meter).

pH Meter

An instrument with a glass electrode selectively sensitive to H+ concentration, used for accurate pH determinations.

pH Formula

pH = log 1/[H+] = -log [H+]

pOH Formula

pOH = log 1/[OH-] = -log [OH-]

Acid (Arrhenius Definition)

A H+ donor (proton donor).

Base (Arrhenius Definition)

A H+ acceptor (proton acceptor).

Strong Acids

Acids like hydrochloric, sulphuric, and nitric acids that are completely ionised in dilute aqueous solutions.

Strong Bases

Bases like NaOH and KOH that are also completely ionised.

Weak Acids and Bases

Acids and bases that are not completely ionised when dissolved in water; common in biological systems.

Conjugate Acid-Base Pair

A proton donor and its corresponding proton acceptor (e.g., Acetic acid (CH3COOH) and acetate anion (CH3COO-)).

Dissociation Constant (Ka)

Equilibrium constant for ionisation reactions, indicating the tendency of an acid to lose a proton.

pKa

pKa = log 1/Ka = -log Ka ; analogous to pH, indicates acid strength (lower pKa = stronger acid).

Titration

A method used to determine the amount of acid in a given solution by neutralizing it with a strong base of known concentration.

Henderson-Hasselbalch Equation

Relates pH, pKa, and the ratio of the concentrations of the proton acceptor and donor: pH = pKa + log [A-]/[HA]

Buffer Capacity

The number of moles of acid or alkali that must be added to 1 litre of buffer to change its pH by 1 unit.

Buffer Molarity

The sum of the molarities of its component molecules.

Ideal Buffer pKa

Should be between 6 and 8, the range in which most biological reactions take place.

Zwitterionic Buffers

Contain both positive and negative charge so do not pass through biological membranes