A base is a fundamental category of many compounds whose water-based solutions have a bitter taste, a slippery feel in water, turn red litmus paper blue, and can react with acids to form salts. A base, also known as an alkali, has a pH higher than 7; a strong base will have a pH of 13 or higher.
Specific types of bases include:
- Arrhenius base: any chemical that increases the number of free hydroxide ions (OH-) when they're added to a water-based solution. The more ions produced, the stronger the acid.
- Brönsted or Brönsted-Lowry base: any chemical that acts as a proton acceptor in a chemical reaction.
- Lewis base: any chemical that donates two electrons to form a covalent bond during a chemical reaction.
In biology, "base" also refers to a nitrogenous base, which is a nitrogen-containing molecule having the chemical properties of an alkali. Examples include adenine, thymine, guanine, and cytosine.
From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.