begin mathsize 36px style p H space equals space 1 half p K subscript a space minus 1 half log C end style

Ka =  Acid Dissociation Constant ; C = Concentration of the Acidic Soluiton ;

pH = -log[H+] ; pKa = -logKa

 

pKa

pH

C

 
The ionization of an acid in water measures the relative strength of the acid. For simplicity we denote strength of an acid in term of -log[H+]. It can be inferred that a higher value of Ka resemble stronger acid. Thus a lower value of pKa (since pKa = -logKa ) which -logKa will resemble a stronger acid. For aqueous weak acid the pH is aproximated and it bears the above relation with Concentration (C) and pKa. Here is a table of pKa Values:
 

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