DEFINTION OF pH SCALE

WHAT IS pH SCALE?
                              A measure of acidity or alkalinity of water-soluble substances (pH stands for 'potential of Hydrogen'). A pH value is a number from 1 to 14, with 7 as the middle (neutral) point. Values below 7 indicate acidity which increases as the number decreases, 1 being acidic. Values above 7 indicate acidity which increases as the number decreases, 1 being the most acidic. Values above 7 indicate alkalinity which increases as the number increases. 14 being the most alkalinity which increases as the number increases from 14 being the most alkaline. This scale, however, is not linear scale like a centimetre of inch scale ( in which two adjacent value have the same difference). It is a logarithmic scale in which two adjacent values increase or decrease by a factor of 10.


pH:
       In chemistry, pH is a logarithmic scale used to specify the acidity or basicity of an aqueous solution. It is approximately the negative of the base 10 logarithm of the molar concentration, molar concentration, measured in units of moles per litre, of hydrogen ions. More precisely it is the negative of the base 10 logarithm of the activity of the hydrogen ion. solutions with a pH less than 7 are acidic and solutions with a pH greater than 7 are basic. Pure water is neutral at pH 7 (25degree celsius ) being neither an acid nor a base. contrary to popular belief, the pH value can be less than 0 or greater than 14 forvert strong acids and bases respectively.


     Measurements of pH are important in agronomy, medicine, chemistry, water treatment, and many others applications.


     The pH scale is traceable to a set of standard solutions whose pH is established by international agreement. Primary pH standard values are determined using a concentration cell with transference by measuring the potential difference  between a hydrogen electrode and a standard electrode such as the silver chloride electrode. The pH of aqueous solutions can be measured with a glass electrode and a pH meterr, or an indicator.
     
   There are three current theories used to describe acid-base reaction : Arrhenius, Bronsted-Lowry and Lewis when determining pH.

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