pH Value


6.2  pH Value

 The pH scale

  • The pH scale is a set of number that determines the degree of acidity or alkalinity of a substance.
  • The pH value would be:
    • 7 for neutral substance. 
    • > 7 for alkaline substance (\(OH^- > H^+\))
    • < 7 for acidic substance (\(H^+ > OH^-\)\(OH^-\))


\(\xleftarrow[]{\textbf{Acidity } \uparrow}\) Neutral \(\xrightarrow[]{\textbf{Alkalinity } \uparrow}\)
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14


  • pH: a logarithmic measurement of the concentration of hydrogen ions, \(H^+\) contained in an aqueous solution.


Formula for pH
\(pH = -log[H^+]\)


  • The concentration of hydroxide ions, \(OH^-\) is also used to calculate the pOH value.


Formula for pOH
\(pOH = -log[OH^-]\)


Relationship of pH with pOH
\(\begin{aligned} pH + pOH &= 14\\ pH&=14-pOH \end{aligned}\)


Hubungan nilai pH dengan kepekatan ion hidrogen dan ion hidroksida 


Relationship of concentration \(H^+\) with pH
  Concentration \(H^+\) \(\uparrow\), pH value \(\downarrow\)  


Relationship of concentration \(OH^-\) with pH
  Concentration \(OH^-\, \uparrow\),   pH value \(\uparrow\)  


Measurement of the pH value of a solution

  • The pH value can be measured by using:

Universal indicator

  • The universal indicator will change colour, and it indicates what the pH based on the colour produced is.
  • The universal indicator can be found in two forms; solution or paper strips. 


pH meter

  • The pH meter is an instrument that is used to measure the pH value of a solution accurately.
  • pH meter shows the number of the pH value in the screen.