6.1.2 Bases and Alkali
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Bases
- Bases are compounds which react with acid to form a salt and water as only products.
- Bases that soluble in water are called alkalis.
- In aqueous solution, alkali it produces hydroxide ions (OH–). In short, alkalis are substances that form hydroxide ions (OH–(aq)) in water
Example
Sodium hydroxide NaOH gives Na+(aq) and OH–(aq) ions,NaOH → Na+ + OH–calcium hydroxide Ca(OH)2 gives Ca2+(aq) and 2OH–(aq) ions.
Ca(OH)2 → Ca2+ + 2OH–Ammonia give NH4+ and OH–
NH3 + H2O → NH4+ + OH–[Note: an alkali is a base soluble in water.]
- In alkaline solution there are more OH– ions than H+ ions.
Physical Properties of Alkali
The following are the physical properties of alkali
- Alkalis are bitter in taste.
- 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. - Alkalis are soapy to touch.
- 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. - 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.