Bases are substances that are slippery to touch when in aqueous form. They taste bitter and change the color of red litmus paper to blue. Bases also dissociate in the water like acids, but instead of producing H+ they produce OH- i.e. hydroxyl ion. If a base dissolves in water then it is called an Alkali. Alkalines become less alkaline when mixed with acids. The pH level of bases ranges from 8-14.
Some common household products are bases. For example, caustic soda and drain cleaner are made from sodium hydroxide, a strong base. Ammonia or an ammonia-based cleaner such as window and glass cleaner is basic. These stronger bases may cause skin irritation. Other bases, like cooking ingredients sodium bicarbonate (baking soda) or cream of tartar are basic, but these are not harmful and suitable for cooking.
1. Bases are slippery to touch when in aqueous form.
2. A base will usually taste bitter.
3. The pH level of a base is from 8 to 14.
4. Bases react with acid to form salt and water.
5. A base will turn red litmus to blue.
They are usually classified on the basis of strength, concentration and on its acidity.
Just like acids, the strength of bases depends on the number of hydroxyl ions it produces when dissolved in water. A high amount of hydroxyl ions represents a strong base and a low amount of hydroxyl ions represents a weak base.
a. Strong base – A base the dissolves completely or almost completely in water is known as a strong base. For example, NaOH, KOH, Ca(OH)2, etc.
\(Na^+OH^- + H_2O → Na^+ (aq) + OH^-(aq)\)
b. Weak base – A base that doesn’t dissolve completely is called a weak base. For example, Ma(OH)2, NH4OH, etc.
c. Super base – A superbase is even better at deprotonation than a strong base. These bases have very weak conjugate acids. Such bases are formed by mixing an alkali metal with its conjugate acids. Such bases are formed by mixing an alkali metal with its conjugate acid. A superbase cannot remain in aqueous solution because it is a stronger base than the hydroxide ion. An example of a superbase in sodium hydride (NaH). The strongest superbase is the ortho-diethynylbenzene dianion (C6H4(C2)2)2−.
d. Neutral base – A neutral base is one which forms a bond with a neutral acid such that the acid and base share an electron pair from the base.
e. Solid base – A solid base is active in solid form. Examples include silicon dioxide (SiO2) and NaOH mounted on alumina. Solid bases may be used in anion exchange resins or for reactions with gaseous acids.
The concentration of the base depends upon the amount of base dissolved in water. It is of two types i.e. concentrated and dilute base.
a. Concentrated base – An aqueous solution that has a relatively high percentage of the base is a concentrated base. For example, concentrated sodium hydroxide, concentrated potassium hydroxide, concentrated ammonium hydroxide, etc.
b. Diluted base – An aqueous solution that has a relatively low percentage of the base is a dilute base. For example, dilute sodium hydroxide, dilute potassium hydroxide, dilute ammonium hydroxide, etc.
The acidity of a base depends on the number of hydroxyl ions it contains. It also depends on the number of hydrogen ions with which a base can combine as one hydrogen ion combines with one hydroxyl ion. It is usually of three types Monoacidic base, Diacidic base, and Triacidic base.
a. Monoacidic base – It is a base that contains only one hydroxyl ion and only combines with one hydrogen ion. For example, NaOH, KOH, NH4OH, etc.
\(NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)\)
b. Diacidic base – It is a base that contains two hydroxyl ions and combines with three hydrogen ions. For example, Mg(OH)2, Fe(OH)2, Zn(OH)2 etc.
\(Ca(OH)_2 (aq) + 2HCl (aq) → CaCl_2 (aq) + 2H_2O (l)\)
c. Triacidic base – It is a base that has three hydroxyl ions and combines with three hydrogen ions. For example, aluminium hydroxide
\(Al(OH)_3 (aq) + 3HCl (aq) → AlCl_3 (aq) + 3H_2O(l)\)
Bases can be used to neutralize acids. When a base, often OH- accepts a proton from acid, it forms a water molecule that is harmless. When all of the acids and bases react to form water molecules and other neutral salts, it is called neutralization.
Acids can also be used to neutralize bases.
Every base has a conjugate acid formed by adding a hydrogen atom to the base. For example, NH3 (ammonia) is a base and its conjugate acid is the ammonium ion, NH4+.
A weak base forms a strong conjugate acid and a strong base form a weaker conjugate acid. Since ammonia is a moderately strong base, ammonium is a considerably weaker acid.
