Organic chemistry/Acid-base chemistry
Acid/Base chemistry began with the Bronsted-Lowry model of acids and bases. This model states molecules containing hydrogen ions are acids, while molecules containing hydroxyl (-OH) functional groups are bases. This is not necessarily true. The recent definition of an acid and a base is based upon how the substance ionizes in water. Acids produce positively charged molecules, while bases produce negatively charged molecules. This definition allows for bases such as ammonia which does not contain an hydroxide ion. The relative strength of acids and bases is measured by their respective ion concentrations once dissolved. The product of the positive ion concentration times the negative ion concentration equals 1*10 to the -14th power. The pH is equal to -log of the positive ion concentration. The pOH is equal to the -log of the negative ion concentration. Thus, pH is measured on a scale of 0 to 14, with 7(th pH of water) as neutral. Each "step" below 7 is ten times more acidic (since it was derived from a power of ten). While rare, substances can have pH levels below 0 or above 14. However, the pH plus pOH of a substance will always equal 14.
Reactions between acids and bases always produce water and a salt. Reactions between acids and metal always produce a salt and hydrogen gas.