# 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.)