which are the methods used for expressing concentration?

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

% w/w 

Example: 10%  solution w/w means  of  is dissolved in  of the solution. (It means   is dissolved in of )

(ii) Weight to volume percent

% w/v 

Example: 10%  (w/v) means   is dissolved in  of solution.

(iii) Volume to volume percent

% v/v 

Example:10% ethanol (v/v) means  of ethanol dissolved in  of solution.

(iv) Volume to weight percent

% v/w 

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  centinormal,

 or 0.001= millinormal

Mathematically normality can be calculated by following formulas,

(i) 

(ii) N

(iii) 

(iv) 

(v) ,

(vi)

(vii)

(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 

Similarly, 

(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 

(xv) 

(* 1 equivalent = 1000 milliequivalent or meq.)