Alkali

In chemistry, an alkali is an aqueous (from water) solution with a pH value of more than 7. The word 'Alkali' comes from the Arabic 'qali' meaning 'from the ashes' since ashes mixed with water used as cleaning products (such as soaps) are made of alkali materials.

Example

• An alkali is where a base is dissolved in water. Often it is the salt of an Alkali metal.
• An alkali is the opposite to an acid and can be neutralised (brought down to pH 7) by adding acid.

Characteristics

• It feels soapy
• It is corrosive (it can burn your skin away)
• The higher the number is over 7 on the pH scale the stronger the alkali is.
• Highly soluble (can be dissolved) in water
• They have a bitter taste
• Turns red litmus paper blue
• Can conduct electricity due to the presence of mobile ions
• Is blue or purple on universal indicator

Strength

Like acids, alkalis can be weak or strong, depending on the nature and the concentration of the ionic salt composing it. The strength of an alkali can be found using universal indicator. Also like acids, the strength of an alkali is rated using the pH scale.

For example, soap and toothpaste contain weak alkalis, while cleaning products often contain strong ones.

Sodium Hydroxide

Examples of common alkalis

• Sodium hydroxide, NaOH
• Potassium hydroxide, KOH
• Calcium hydroxide, Ca(OH)₂
• Aqueous ammonia, NH₃ (aq)
• Magnesium hydroxide, Mg(OH)₂

Uses of common alkalis

• Sodium hydroxide is used to make paper, detergents and soap.
• Potassium hydroxide is used by farmers to make acidic soil more alkaline so that plants will grow better in it, and is also used as the electrolyte in alkaline, Ni-Cd, and Ni-MH batteries.
• Calcium hydroxide is used to neutralize acidic soil.
• Ammonium hydroxide is used as a cleaning agent.

Oxides and hydroxides

Metal oxides and metal hydroxides are two types of base. When neutralised (an acid is added) they produce a salt and water. The type of salt produced depends on the acid and base.

Related pages

• Base
• Acid

Other websites

• Small article on Alkaline chemicals
• A distributor of Alkali Metals
• A revision site directed towards GSCE students Archived 2007-06-08 at the Wayback Machine
• In depth article on Alkalis - not recommended for Simple Wikipedia users
• Alkali cleaning materials
• Small in depth article on Alkali Metals Archived 2007-08-17 at the Wayback Machine