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Bases

The following are the physical properties of alkali

  1. Alkalis are bitter in taste. 

  2. Alkalis turn litmus from red to blue.
    Like acid, alkali can change the colour of litmus. In alkali solution, the colour of litmus turn blue.

  3. Alkalis are soapy to touch. 

  4. Alkalis has pH value more than 7
    pH value is a measurement of the concentration of hydrogen ions in a solution. Alkali has very low concentration of solution hydrogen ion, even lower than water. Hence the pH value of alkali is higher than 7. (Note: The pH value of water is 7. The lower the concentration of hydrogen ions, the higher the pH value.

  5. Alkalis can conduct electricity
    When a base dissolve in water, it will dissociate and form hydroxide ions. The present of the freely move ions make alkali an electrolyte.

Physical Properties Of Alkali
Chemical Properties Of Bases/Alkalis

  1. Alkalis react with acids to form a salt and water — this is a neutralisation reaction:

  2. Alkalis, when warmed with ammonium salts, give off ammonia gas:

Ammonia as an Alkali

  1. By nature, ammonia is a covalent compound.

  2. Ammonia exists as gas at room temperature.

  3. Ammonia gas is soluble in water.

  4. Physical properties of ammonia:

    1. Pungent smell

    2. Colourless

    3. Turn litmus from red to blue

Strength Of Alkalis

  1. Similar to strength of acids, the strength of an alkali is defined by its ability to ionise and release hydroxide ions (OH-) in the solution.

  2. In a solution of strong alkali, all the alkali molecules are ionised in the water to produce hydroxide  ions.

  3. In a solution of weak alkali, only small portion of the molecules are ionised to release hydroxide ions.

  4. Table below shows some example of strong/weak alkalis.

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