Direct or indirect titration? 

When the titration reaction consumes the chemical of interest E_int we use the term direct titration (ν₁T + ν₂E_int = products): only one reaction occurs.

When the titration reaction consumes a chemical whose concentration is related to the chemical of interest E_int, we use the term indirect titration: several reactions may occur.

When two successive reactions take place, a chemical A in excess reacts with E_int in a total manner to create chemical B (ν_AA + ν_intE_int = ν_BB + products).

Two types of titration may then be carried out:
1. The newly created chemical B is titrated (ν_TT + ν’_BB= products).
2. Titration of the excess of chemical A that did not react with E_int (ν_TT + ν’₁A_exc = products). In this case we speak of return titration.