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The electrode is used as the negative electrode of the galvanic battery, and the electrode symbol can be written
.
For example, the electrode reaction of a standard hydrogen electrode is
2H + + 2E - = H 2
The electrode symbol of the standard hydrogen electrode can be expressed as
Pt|H 2 (100kPa)|H + (1 mol·dm -3 )
1.
Metal-metal ion electrode
The metal electrode plate is immersed in its cation solution to form a metal-metal ion electrode
.
The copper electrode and zinc electrode in the Cu-Zn galvanic battery belong to this type of electrode
Using the electrode as the negative electrode of the galvanic battery, the electrode symbol can be written, and the electrode reaction can be written from the electrode symbol
.
For example, the electrode symbol and electrode reaction of copper electrode and zinc electrode are
2.
Gas-ion electrode
The inert metal is immersed in a solution of gas and its ions to form a gas-ion electrode
.
For example, the standard hydrogen electrode is this kind of electrode, the electrode symbol is Pt|H 2 (p)|H + (c), the electrode reaction
2H + + 2E - = H 2
The electric pair Cl 2 /CI- can also be designed as a gas-ion electrode, the electrode symbol is Pt|Cl 2 (p)|Cl-(c), the electrode reaction
Cl 2 + 2E - = 2Cl -
3.
Metal-insoluble salt (or oxide)-ion electrode
The metal surface is covered with a layer of insoluble salt (or oxide) of the metal, and it is immersed in a solution (or acid or alkali) containing the insoluble salt anion to form a metal-insoluble salt (or oxide)- Ion electrode
.
The most important of these types of electrodes are the silver chloride electrode and the finely lead saturated calomel electrode
The silver chloride electrode is formed by covering a layer of AgCl on the surface of the silver wire and immersing it in a hydrochloric acid solution
.
E + electrode reaction AgC1 - = CI of Ag + -
Symbol electrode Ag | AgC1 | CI - (c)
The mercury-saturated calomel electrode is the most commonly used reference electrode (Figure 8-5)
.
The standard hydrogen electrode uses strict conditions, hydrogen is not easy to purify, and platinum black is easy to poison, so it is not often used in actual measurement
Electrode reaction Hg 2 CI 2 + 2E - = 2Hg + 2Cl -
Symbol electrodes of Pt | Hg | Hg 2 CI 2 | CI - (C)
Figure 8-5 Schematic diagram of saturated calomel electrode
4.
Redox electrode
The inert metal is immersed in a mixed solution of two different valence ions of a certain element to form a redox electrode
.
The characteristic of the redox electrode is that no elemental substance participates in the electrode reaction
For example, a platinum wire is immersed in a mixed solution of Fe 2+ and Fe 3+ to form a redox electrode
Electrode symbol Pt|Fe 3+ (c1), Fe 2+ c2)
Electrode reaction Fe 3+ +e-=Fe 2+
The platinum wire is immersed in an acidic solution of Cr 2 O 7 2- and Cr 3+ , which also constitutes a redox electrode
Electrode symbol Pt|Cr 2 O 7 2- (c1), Cr 3+ (c2)
Electrode reaction of Cr 2 O .
7 2- + 14H + + 6E - = 2Cr 3+ + 7H 2 O
