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pH Scale

• The pH of a solution indicates the hydrogen ion concentration([H⁺]) of that solution.
  
  
• The concentration of hydrogen ions ([H⁺]) are given in molar units (M).
  
  
• The [H⁺] (hydrogen ion concenration) in molar units (M) are usually very small.
  
  In the order of 1/1,000,000 M to 1/10 M, which can be represented by 10 ^{- 6} and 10 ^{- 1} molar units respectively.
  
  
• As [H⁺] consist usually of only negative powers (e.g. 10 ^{- 6} and 10 ^{- 1}), only the power number as a positive number is used to represent the [H⁺] (e.g. 6 and 1 respectively).
  
  
• That is, pH = - Log ₁₀ [H⁺] (M), where pH is used to represent the [H⁺].
  
  or a [H⁺] of 10 ^{- 5} M has a pH of five (5)
  
  or pH values represent the negative log of the hydrogen ion concentration ([H⁺]) to the base ten (10)
  
  or the negative power to the base of 10 of a hydrogen ion concentration of 10 ^{- 6} is -(-6) therefore the pH = 6.
  
  
• pH is a symbol from the German word potenz = power and H from Hydrogen.
  
  
  That is the power value of the hydrogen ion concentration presented as a positive number.
  
  This explains why an increase in acidity, or hydrogen ion concentration ([H⁺]), results in a lower pH value.
  
  (i) [H⁺] = 0.001 M = 1/1000 M = 1/10³ M = 10 ^-3 M = pH 3.00
  
  (ii) [H⁺] = 0.01 M = 1/100 M = 1/10² M = 10 ^-2 M = pH 2.00