Although often considered synonymous with base, alkalis represent a subset of bases, defined as either the group of alkaline earth metals or basic salts composed of them or more broadly any base that forms hydroxide ions when dissolved in water. The word alkali (and the adjective alkaline) comes from the Arabic word al qaliy which means the calcified ashes and referred to the products of calcination-usually the burning of lime to produce cement. Some etymological dictionaries give the Arabic qala, to roast in a pan. The English word kiln is often supposed to come from culina (kitchen) an unexplained variant of coquere, to cook. Perhaps there is a missing Proto Indo-European root to link these words for cooking and roasting.
The modern usage of alkali dates to 1813. The alkali metals include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs) and francium (Fr). Found along the left side of the Periodic Table, the alkali metals are all highly reactive. The alkaline earth metals contain beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and radium (Ra). The alkalline earth metals occupy the second left most row of the Periodic Table and are also very reactive.
Mono Lake, California, pictured above, is an alkali lake with an unusual ecosystem based on brine shrimp that utilizes the heavy salt concentration. The lake was briefly famous when NASA discovered an organism that is capable of metabolizing arsenic in December 2010.
Image courtesy NASA.