Acid Dissociation of the Carbon-Hydrogen Bond

Because the salts have different colors, it is easy to tell whether the reaction of a salt with a given carbon acid goes to completion in either direction. 

This has been used to rank hydrocarbons in a series of increasing acidity in the solvent ether 842 

Spectrophotometry has been used in the measurement of the dissociation constants of some weak acids using the color of the ion as an indicator. The dissociation constant of tris-(/ -nitrophenyl)-methane in ethanolic sodium ethoxide at 25° is 3.66 X 10-18.848 Another method makes use of the difference in optical rotation between menthol and sodium mentholate to find the position of the equilibrium 844 

Quantitative measurements of the strength of an acid are best based on electrometric measurements of the pH of the partly neutralized solution. Conductivity measurements are likely to give ionization constants that are too high due to the presence of conducting impurities. Estimates of acid strength from rate data are also somewhat unreliable 

The acids shown below are all strong, that is to say off-scale, in water.347 

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