What is a base?
The ionic compounds that produce negative hydroxide (OH−) ions when dissolved in water are called bases. A compound containing negative nonmetal ion as well as a positive metal ion that are held together by the ionic bond is called an ionic compound. But what are ions? Ions are atoms which become charged particles as a result of losing or gaining electrons. NaOH (sodium hydroxide) is an example of a base. When it dissolves in water, it generates negative hydroxide (OH−) ions and positive sodium (Na+) ions. It can be represented by the following equation:
NaOH →H2O OH− + Na+
Types of bases:
- Strong base – It is a compound that has an ability to remove a proton from a very weak acid. Or they completely dissociate into its ions when in water. Examples are potassium hydroxide (KOH), sodium hydroxide (NaOH).
- Weak base – There is incomplete dissociation when in water. The aqueous solution contains both the weak base as well as its conjugate acid. Examples are ammonia (NH3), water (H2O), pyridine (C5H5N).
- Superbase – These bases are better at deprotonation when compared to a strong base. These have very weak conjugate acids. They can be obtained by mixing an alkali metal with its conjugate acid. It can’t sustain in aqueous solution as it is a stronger base than hydroxide ion. Examples are sodium hydride (NaH), ortho-diethynylbenzene dianion (C6H4(C2)2)2−
- Neutral base – It forms a bond with a neutral acid share an electron pair.
- Solid base – It is active in solid form. Examples are silicon dioxide and sodium hydroxide mounted on alumina.
Examples of Bases:
Rubidium hydroxide (RbOH)
Rubidium hydroxide is a strong base. It appears as a greyish white solid and has a formula RbOH. It is also known as rubidium hydrate. It is prepared in a lab as it does not occur naturally. It has a molecular mass of 102.475 g/mol and density of 3.2 g/cm³. The boiling point is 1,390 °C melting point is 301 °C. It is highly corrosive. When comes in contact with skin causes burns. It is used in scientific research.
Zinc hydroxide (ZnOH)2
Zinc hydroxide is a weak base. It appears as a white powder and has a chemical formula (ZnOH)2. It occurs naturally and can also be prepared in the lab. It can be obtained by adding sodium hydroxide to a zinc salt solution. It has a molecular mass of 99.424 g/mol and density of 3.053 g/cm³. It has a melting point of 125 °C. It is used surgical dressings as an absorbent.
Properties of Base:
- Aqueous base solution dissociates into ions to conduct electricity.
- It has a pH value greater than 7.
- They form salts on reacting with acids.
- They help in promoting certain chemical reactions.
- They are bitter to taste if placed in alkali solutions.
- Strong or concentrated bases are caustic.
- It changes the indicator colour from red litmus paper to blue litmus paper.
- It has the ability to accept protons from proton donors.
- It contains OH− ions.
- They vigorously react when in contact with acids.
- They are slippery to touch.
- They conduct electricity when dissolved in water.
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