Blog

Bases

Bases:

 

A base is any metal oxide or hydroxide. This means that a base contains either oxide ions O2- or hydroxide ions OH–.

We can also define a base as a substance that reacts with an acid to give a salt and water only.

base + acid -> salt + water

 

For example,

 

CuO (s) + H2SO4 (aq) -> CuSO4 (aq) + H2O (l)

 

In this case, copper (II) sulphate CuSO4 is the salt produced.

 

Another example,

 

NaOH (aq) + HCl (aq) -> NaCl (aq) + H2O (l)

 

In this case, sodium chloride NaCl is the salt produced.

 

Note in the above cases, the oxide ions or the hydroxide ions from the bases react with the hydrogen ions from the acids to form water. This reaction is known as neutralization, and it is represented by the ionic equation below.

OH– (aq) + H+ (aq) -> H2O (l)

 

It occurs between alkalis and acids.

 

 

Alkalis:

An alkali is a base that is soluble in water. In an aqueous solution, an alkali produces hydroxide ions OH–.

Most bases are insoluble in water. They are not considered as alkalis. Some common examples of alkalis include sodium hydroxide NaOH, potassium hydroxide KOH, calcium hydroxide Ca(OH)2 and aqueous ammonia NH3.

 

Properties of Alkalis:

  1. Alkalis have a bitter taste and a soapy feel.
  2. They have a pH above 7.
  3. The higher the PH, the more corrosive they are.
  4. They turn red litmus paper blue.
  5. All alkalis produce hydroxide ions when dissolved in water.
  6. All alkalis can react with water to form salt and water only. This is known as neutralization. We have already discussed this.
  7. Alkalis heated with ammonia salts give off ammonia gas.     alkali + ammonium salt -> ammonia + salt + water
  8. Alkalis can react with a solution of one metal salt to give a metal hydroxide and another metal salt.   alkali + salt (of metal A) -> metal hydroxide + salt (of metal B)