Acids and Bases

Conjugate base

An acid that has lost its hydrogen ion.

Conjugate acid

A base that has gained a hydrogen ion.

Strong acid

An acid that dissociates 100% into ions.

Weak acid

An acid that does not dissociate 100%.

Strong base

A base that is 100% ionized in solution.

Weak base

A base that is less than 100% ionized.

Strong Acid

Hydrobromic acid (HBr), Perchloric acid (HClO4), Hydrochloric acid (HCl), Hydroiodic acid (HI), Chloric acid (HClO3), Sulfuric acid (H2SO4), Nitric acid (HNO3).

Weak Acid

Formic acid (HCOOH), Acetic acid (CH3COOH), Trichloroacetic (CCl3COOH), Hydrofluoric (HF), Hydrocyanic (HCN), Hydrogen sulfide (H2S), Water (H2O).

Strong Base

Sodium hydroxide (NaOH), Potassium hydroxide (KOH), Lithium hydroxide (LiOH), Rubidium hydroxide (RbOH), Cesium hydroxide (CsOH), Calcium hydroxide (Ca(OH)2), Barium hydroxide (Ba(OH)2), Strontium hydroxide (Sr(OH)2).

Weak Base

Ammonia (NH3), Trimethyl ammonia (N(CH3)3), Pyridine (C5H5N), Ammonium hydroxide (NH4OH).

pH

A unit that describes the acidity and alkalinity of a solution.

pH expression

pH = -log [H+].

Significance of pH

Important for oxygen transport, enzyme activity, and generation of metabolic energy. Many biological reactions depend on the charge of the molecule, which is determined by the pH of the solution.

Buffer solution

A solution that resists pH change on addition of a small quantity of acid/base.

Acidic buffer

A weak acid and its salt with its conjugate base (e.g., CH3COOH/CH3COONa).

Basic buffer

A weak base with its salt (main contributor of ions) with its conjugate acid (e.g., NH4OH/NH4Cl).

Intracellular buffer systems

Phosphate, Protein, Hemoglobin, Amino acid.

Extracellular buffer systems

Protein, Carbonic acid-bicarbonate, Plasma protein, Amino acids.

Chemical buffer system

Bicarbonate, Phosphate, Protein.

Physiological buffers

Respiratory mechanism (CO2 excretion), Renal mechanism (H+ excretion).

Henderson-Hasselbalch equation

Used to calculate the pH of a buffer solution. pH = pKa + log ([A-]/[HA]).

pKa

The -log of the acid dissociation constant, which indicates the strength of an acid.

Applications of Henderson-Hasselbalch equation

Predicting acid behavior at a specific pH, determining solubility from pH, determining protein isoelectric point.