Acid, bases and salts

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KHSO4(aq) + KOH ================ K2SO4(aq) + H+O(l)

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Basic Salts:

Basic salts contain the hydroxide ion, OH-. They are formed when there is insufficient supply of acid for the complete neutralization of the base. A basic salt will turn red litmus blue and will react with excess acid to form normal salt.

Zn(OH)2(s) + HCl(aq)  Zn(OH)Cl(aq) + H2O(l)

Zn(OH)Cl(aq) + HCl(aq)  ZnCl2(aq) + H2O(l)

Mg(OH)2(s) + HNO3(aq)  Mg(OH)NO3(aq) + H2O(l)

Mg(OH)NO3(aq) + HNO3(aq)  Mg(NO3)2(aq) + H2O(l)

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Hydrated & anhydrous salts

Hydrated Salt: Salt that contains Water of Crystallization is called Hydrated Salt e.g. CuSO4.5H2O, Na2CO3.10H2O.

Anhydrous Salt: Salt with out Water of Crystallization is called Anhydrous Salt. e.g. CuSO4, Na2CO3

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Uses of salts

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Self Ionization of Water

Pure water is often used as an example of non- conducting liquid. In fact water will conduct electricity if there is sufficient electrical energy present. The fact that pure water conduct electricity suggest that it contains ions. The ions present are due to water undergoing self ionization.

2H2O(l) ========== H3O+(aq) + OH- (aq)

The concentration of H3O+ ions in pure water at 25oC is 10-7 moles/dm3. The concentration of OH- ion should also be 10-7 moles/dm3.

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The pH Scale

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The pH scale is a measure of the relative acidity or alkalinity of a solution.

It is defined as negative log of H+ ion concentration.

pH = -log [H+]

Water is a neutral liquid with a pH of 7 (green). When a substance dissolves in water it forms an aqueous solution that may be acidic, neutral or alkaline.

Acidic solutions have a pH of less than 7, and the lower the number, the stronger the acid is

Neutral solutions have a pH of 7. These are quite often solutions of salts, which are themselves formed from neutralizing acids and bases.

Alkaline solutions have a pH of over 7 and the higher the pH the stronger is the alkali. Weak alkalis like ammonia give a pH of 10-11 but strong alkalis like sodium hydroxide give a pH of 13-14.

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pH

A change of 1 in pH is a tenfold increase in acid or base strength.