Hydrogen Ion Concentration – pH Scale

Hydrogen Ion Concentration – pH scale

Sorensen, a Danish biochemist developed a scale to measure the acidity in terms of concentrations of  in a solution. As defined by him, “pH of a solution is the negative logarithm to the base 10 of the concentration of H+ ions which it contains.”

 or

Just as pH indicates the hydrogen ion concentration, the pOH represents the hydroxyl ion concentration, i.e.,

Considering the relationship,

Taking log on both sides, we have

or

or      

  [H+] [OH] pH pOH
Acidic solution > 10–7 < 10–7 < 7 > 7
Neutral solution 10–7  10–7 7 7
Basic solution < 10–7 > 10–7 > 7 < 7

 

pH of some materials

Material pH Material pH
Gastric juice 1.4 Rain water 6.5
Lemon juice 2.1 Pure water 7.0
Vinegar 2.9 Human saliva 7.0
Soft drinks 3.0 Blood plasma 7.4
Beer 4.5 Tears 7.4
Black coffee 5.0 Egg 7.8
Cow’s milk 6.5 Household ammonia 11.9

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