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.)