The word alkali can mean:-

• In chemistry, an alkali is a specific type of base, formed as a carbonate or hydroxide salt of an alkali metal or alkali earth metal element. Sometimes the word alkali is used to refer to any base but this is a misnomer derived from the fact that most common bases are alkalis.
• In the western parts of the USA, natural soda or potash deposits (soda and potash themselves are both alkali salts).
• Alkali Springs is a place in Oregon in the USA.

Common properties of alkalis

Alkalis are all Arrhenius bases and share many properties with other chemicals in this group (Arrhenius bases form hydroxide ions when dissolved in water). Common properties of alkaline solutions include:

• Alkalis all form aqueous solutions.
• Alkalis are bitter to taste (compared with acid solutions which are described as sour).
• Caustic (causing chemical burns).
• Slippery or soapy to the touch (due to the caustic reaction dissolving the surface of the skin and fingerprint).
• Alkalis have a pH greater than 7 and hence can be detected with litmus paper (litmus will turn blue on contact with an alkali).

Confusion between base and alkali

The terms base and alkali are often used interchangeably, since most common bases are alkalis. It is common to speak of "measuring the alkalinity of soil" when you actually mean measuring the pH (base property). Similarly, bases which are not alkalis, like ammonia, are sometimes erroneously referred to as alkaline.

Alkali salts

Most basic salts are alkali salts.

Common alkali salts include:

• sodium hydroxide (often called "caustic soda")
• potassium hydroxide (commonly called "potash")
• lye (generic term, for either of the previous two, or even for a mixture)
• calcium carbonate (sometimes called "free lime")

Alkali soil

Soil with a pH above 7.4 is normally referred to as alkaline. This soil property can occur naturally, due to the presence of alkali salts. Although some plants do prefer slightly basic soil (including cabbage family vegetables and buffalograss), most plant prefer a mildly acidic soil (pH between 6.0 and 6.8), and high pH levels can cause a problem.

In alkali lakes (a type of salt lake), evaporation concentrates the naturally occurring alkali salts, often forming a crust of mildly basic salt across a large area.

Examples of Alkali Lakes:

Redberry Lake, Saskatchewan, Canada.

Tramping Lake, Saskatchewan, Canada.

Etymology

The word "alkali" is derived from Arabic al qalīy = "the calcined ashes", referring to the original source of alkaline substance. Ashes were used in conjunction with animal fat to produce soap, a process known as saponification.