Bases and Alkalis

Bases and Alkalis

A base is a compound that reacts with and neutralises an acid. The

reaction forms a salt plus water.

Alkalis are a type of base - ones that dissolve in water. Alkalis are

compounds that react and neutralise acids. Like bases, they form a

salt and water in the reaction.

Alkalis turn red litmus indicator paper blue and they cause Universal

Indicator paper to turn blue or purple. Alkaline solutions have a pH

value greater than 7. Alkaline solutions feel soapy and are corrosive.

Examples of bases and alkalis:

NAME

FORMULA

DOES IT DISSOLVE IN WATER

ALKALI OR BASE

FOUND IN/USED FOR

Copper oxide

CuO

No

Base

Sodium hydroxide

NaOH

Yes

Alkali pH 13

Used to remove grease from ovens & drains. Used to make soap

Ammonia

NH3

Yes

Alkali pH 10

The main active ingredient in household cleaning fluids

Calcium hydroxide

Ca(OH)2

No

Base

Slaked lime used in agriculture

Aluminium hydroxide

Al(OH)3

No

Base

Used in some indigestion tablets

Acids and Alkalis

Neutralisation

Neutralisation is the reaction of an acid with a base or alkali until

the solution is neutral (pH7). In neutralisation, the acid and base

(or alkali) both lose their properties and the solution becomes

neutral. A salt and water are formed.

Neutralisation is used in the following everyday situations:

* Farmers use an alkali called calcium hydroxide (slaked lime or

lime). This is spread on the fields or ploughed ground. It is used

to neutralise the slightly acidic soil or even to make the soil

slightly alkaline, because grass and vegetable crops often need

often soils with a specific pH to grow well.

* When you get a burning feeling in your throat after you've been