Total systematic error in redox titrations with visual indicators--II. Experimental verification

The equations for calculating the transition potential of a redox indicator and the total titration error have been verified experimentally. Good agreement has been obtained for reversible indicators such as Variamine Blue, 4-methyl-4'-aminodiphenylamine and ferroin. In the latter case it was shown that at the usual concentrations the indicator acts as a one-colour indicator, whereas for higher concentrations its behaviour is typical of a two-colour indicator. In the case of a pseudoreversible indicator--diphenylaminosulphonic acid--the calculated values give only the minimum error. In real conditions the error is always more positive.