Acids are chemicals which will break apart in water (or another solvent) and yield hydrogen ions. For instance:
HCl is an acid because in water in breaks apart to form H+ and Cl- ions.
However, H+ ions react with many compounds. For example, when you put a metal (say copper) in an acid with a high concentration of H+, two H+ ions grab a couple electrons from the metal to form a hydrogen molecule (H2). A charged metal ion (say Cu++) will then go into solution, since it loses some of its electrons.
So the ’acidic nature’ is just another way of saying that acids release a particular ion (H+) that reacts with many other substances, causing them to go into solution.
Bases are compounds that produce OH- ions in water. Sodium hydroxide is a common example:
NaOH -----> Na+ + OH-
OH- and H+ react to form water.
Carbonates (CO3--) are actually weak bases. Carbonic Acid (H2CO3) breaks apart to form H+ and HCO3- or to make two H+’s and CO3--. The fractions found as H2CO3, HCO3-, and CO3-- depend on what the concentration of H+ ions is, which depends both on how much carbonate is present and on what other acids and bases are around. If there’s lot’s of H+ (acidic), it tends to recombine to make H2CO3. If there’s little (basic), then mostly CO3-- will be found.
CO3-2 and HCO3- are what chemists call "the Conjugate Base of a weak acid" since Carbonic acid is a weak acid (it doesn’t entirely break up into H+ and HCO3-; Some of the compound remains as H2CO3 in the solution)
Ions like CO3--, HCO3- as well as SO4--, PO4---, etc in water react to:
CO3-- + H20 ----> HCO3- + OH-
So a carbonate like Na2CO3 forms a weak base in water.
Jason (w mike)
(republished on 07/12/06)