Methods of Expressing Concentration of Solution
Concentration of solution is the amount of solute dissolved in a known amount of the solvent or solution. The concentration of solution can be expressed in various ways as discussed below,
(1) Percentage : It refers to the amount of the solute per 100 parts of the solution. It can also be called as parts per hundred (pph). It can be expressed by any of following four methods,
(i) Weight to weight percent
Example: 10% solution w/w means of is dissolved in of the solution. (It means is dissolved in of )
(ii) Weight to volume percent
Example: 10% (w/v) means is dissolved in of solution.
(iii) Volume to volume percent
Example:10% ethanol (v/v) means of ethanol dissolved in of solution.
(iv) Volume to weight percent
Example: 10% ethanol (v/w) means of ethanol dissolved in of solution.
(2) Parts per million (ppm) and parts per billion (ppb) : When a solute is present in trace quantities, it is convenient to express the concentration in parts per million and parts per billion. It is the number of parts of solute per million or per billion parts of the solution. It is independent of the temperature.
(3) Strength: The strength of solution is defined as the amount of solute in grams present in one litre (or ) of the solution. It is expressed in g/litre or .
(4) Normality (N) : It is defined as the number of gram equivalents (equivalent weight in grams) of a solute present per litre of the solution. Unit of normality is gram equivalents litre–1. Normality changes with temperature since it involves volume. When a solution is diluted times, its normality also decreases by times. Solutions in term of normality generally expressed as,
Normal solution; Penta normal,
Deca normal; semi normal
Deci normal; Penti normal
or 0.001= millinormal
Mathematically normality can be calculated by following formulas,
(viii) If volume and normality is so changed that new normality and volume and then, (Normality equation)
(ix) When two solutions of the same solute are mixed then normality of mixture is
(x) Vol. of water to be added i.e., to get a solution of normality from of normality
(xi) If of an acid is completely neutralised by of base of normality
(xii) When of acid of normality is mixed with of base of normality
(a) If (Solution neutral)
(b) If (Solution is acidic)
(c) If (Solution is basic)
(xiii) Normality of the acidic mixture
(xiv) Normality of the basic mixture
(* 1 equivalent = 1000 milliequivalent or meq.)