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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
- 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
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.
Examples of common Alkalis
- Sodium hydroxide, NaOH
- Potassium hydroxide, KOH
- Calcium hydroxide, Ca(OH)2
- Aqueous ammonia, NH3 (aq)
Uses of common Alkalis
- Sodium hydroxide is used to make paper, detergents and soap.
- Potassium hydroxide is used in farming 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 cleansing 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.