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Some Important Terms

1. Standard Solution

A solution whose concentration is known is called a standard solution. Concentration of a solution is generally expressed as normality or molarity.

2. Normality

Normality of a solution is defined as the number of gram-equivalents of solute in 1 dm3 of solution. It is denoted by N. Mathematically, it may be expressed as:

Normality = Number of gram – equivalents of solute

/ volume of solution (in dm3 or litres)

= Mass of solute (in grams) per dm3 of solution

/ Gram-equivalent mass of the solute

Number of gram equivalents of solute = Normality x Volume of solution ( in dm3)

A solution containing one gram-equivalent of solute per dm3 of solution is called normal solution.

Equivalent mass. Equivalent mass of a substance can be obtained from its molecular mass.

Equivalent mass of an acid is defined as the mass of the acid which can furnish one mole of hydrogen ions.

Equivalent mass of an acid

= molecular mass of acid / number of available hydrogen ions per molecule

= molecular mass of acid / basicity of acid

Similarly, equivalent mass of a base is defined as the mass as the base which can furnish one mole of hydroxyl ions. It may also be defined as the mass of the base which is completely neutralized by one equivalent of the acid.

Equivalent mass of a base

= molecular mass of acid / number of available hydrogen ions per molecule

= molecular mass of acid / Acidity of base

Equivalent mass of a salt = Molecular mass of salt / Total valency o metal ion

Equivalent mass of some compounds (acids, bases and salts) are given in Table 23.1.

Table 23.1. Equivalent Masses of Some Compounds

3. Molarity

Molarity of a solution may be defined as the number of gram moles of solute per dm3 or per litre of the solution. It is denoted by M. Mathematically, it may be expressed as:

Molarity = Gram moles of  solute / Volume of solution (in dm3)

or                                            = mass of solute (in grams) per dm3 of solution

/ gram molecular mass of the solute

Gram moles of solute = molarity of solution (in dm3)

A solution containing one gram mole of solute per dm3 of solution is called molar solution.