Titration analysis method-oxidation-reduction titration method (2)

3.

(1) Redox titration curve

The size of the potential jump near the stoichiometric point is related to the difference in the conditional potential of the two pairs of electricity

Figure 2.

(2) Redox indicator

1) Redox indicator

Each redox indicator changes color within a certain potential range, which is called the electrode potential color range of the indicator

Table 2.

The redox indicator is a general indicator for redox titration

a.

b.

For example: try ferrous iron: Fe(phen) ₃ ²⁺ (red)—→Fe(phen) ₃ ³⁺ (blue)

2) Self indicator

This substance is called a self-indicator

For example: in the KMnO ₄ method, when using MnO ₄ ^- to titrate colorless or light-colored reducing substances in an acidic solution, before the metering point, the dripped MnO ₄ ^-is all reduced to colorless Mn ²⁺ .

3) Special effect indicator

Note: At the moment when the indicator is added, Na ₂ S ₂ O ₃ titrates the water sample to a light yellow color, then adds starch and turns blue.