How to judge the electrolytic cell yin and yang pole?

First look at whether [anode] is an inert electrode (it will be clearly stated in the question)

If it is not an inert electrode, such as copper

Then it is copper to participate in the reaction: Cu-2e = = = Cu2

If it is an inert electrode, only the ions in the solution need to be considered.

The anodes are anions, the cathodes are cations

The anode loses electrons and the cathode gains electrons.

The following examples illustrate

1. Inert electrode electrolysis of water

This is a simple electrolytic reaction.

The solution has H, OH-

The anode (connected to the positive pole of the power supply) is OH-, and the cathode (connected to the negative pole of the power supply) is H

Anode: 4OH -- 4e = = = O₂ 2H O2 O

Cathode: 2H 2e = = = h, that is, 4H 4e = = = 2H [equal gain and loss of electrons]]

The two types add: 4OH- 4H = = = O₂ 2H O2 2H ↑

Ions are coming from water, that is, 4H? O === O₂ 2H? O 2H?

Water elimination: 2H O = = electrolysis = = O↑ 2H ↑ [total reaction]]

2. Inert electrode electrolysis NaCl solution

The anode has Cl-, OH-

Who lost the electronics?

There is a discharge sequence [S->I->Br->Cl->OH-> acid radical ion]]

So it is Cl-discharge: 2Cl-2e = = = Cl

Cathode has H, Na

Reaction sequence: [Ag >Hg2 >Fe3 >Cu2 >H> other active metal ions]]

So it is h reaction: 2H 2e === H₂

The two types add: 2H 2Cl-= = electrolysis = = = H? Cl?

H comes from water: 2H O = = = 2H 2OH-

H: 2h ₂o 2Cl-=== 2OH-h₂^ cl₂^