Alkali
The word "alkali" is derived from Arabic "al qalīy" (or "alkali"), meaning "the calcined ashes" (see calcination), referring to the original source of alkaline substances. A water-extract of burned plant ashes, called potash and composed mostly of potassium carbonate, was mildly basic. After heating this substance with calcium hydroxide ("slaked lime"), a far more strongly basic substance known as "caustic potash" (potassium hydroxide) was produced. Caustic potash was traditionally used in conjunction with animal fats to produce soft soaps, one of the caustic processes that rendered soaps from fats in the process of saponification, one known since antiquity. Plant potash lent the name to the element potassium, which was first derived from caustic potash, and also gave potassium its chemical symbol K (from the German name Kalium), which ultimately derived from alkali.
Alkali metal
Lithium and sodium react with carbon to form acetylides, LiC and NaC, which can also be obtained by reaction of the metal with acetylene. Potassium, rubidium, and caesium react with graphite; their atoms are intercalated between the hexagonal graphite layers, forming graphite intercalation compounds of formulae MC (dark grey, almost black), MC (dark grey, almost black), MC (blue), MC (steel blue), and MC (bronze) (M = K, Rb, or Cs). These compounds are over 200 times more electrically conductive than pure graphite, suggesting that the valence electron of the alkali metal is transferred to the graphite layers (e.g. ). Upon heating of KC, the elimination of potassium atoms results in the conversion in sequence to KC, KC, KC and finally KC. KC is a very strong reducing agent and is pyrophoric and explodes on contact with water. While the larger alkali metals (K, Rb, and Cs) initially form MC, the smaller ones initially form MC, and indeed they require reaction of the metals with graphite at high temperatures around 500 °C to form. Apart from this, the alkali metals are such strong reducing agents that they can even reduce buckminsterfullerene to produce solid fullerides MC; sodium, potassium, rubidium, and caesium can form fullerides where "n" = 2, 3, 4, or 6, and rubidium and caesium additionally can achieve "n" = 1.