Factors Affecting Strength of Acids and Bases

One of the considerations related to acid strength for a polyprotic acid such as H3P04 is the fact that the first proton to be removed is lost more easily than are the second and third. The first proton is 

It will be noted that there is a factor of approximately 105 between successive dissociation constants. This relationship exists between the equilibrium constants for numerous polyprotic acids, and it is sometimes known as Pauling s rule. This rule is also obeyed by sulfurous acid, for which ffj = 1.2 X 10 2 and K2 = 1 X 10 7. 

Another of the important concepts in dealing with acid strength is illustrated by the dissociation constants for the chloro-substituted acetic acids. The dissociation constants are as follows CH3COOH, 

The effect of one chlorine atom in different positions can be seen from the dissociation constants for the monochlorobutyric acids. In the series of acids, a chlorine atom can be attached to the carbon atom adjacent to the COOff group or on one of the other carbon atoms. The dissociation constant for butyric acid is 1.5 X 10 1 When a chlorine atom is attached in the three available positions, the dissociation constants are as follows  

In this series, it is apparent that the effect of the chlorine atom is greatest when it is dosest to the carboxyl group and least when it is farthest away. 

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