Electrolysis is conducted by using direct currentRedox reactionThe principle is that the current passes through a substance and causes a chemical change. The chemical change is that the substance loses or gains electrons (oxidation orreduction）Process.During electrolysis, the device that converts electric energy into chemical energy is an electrolytic cell. The electrolysis process isElectrolytic cellIn.
Chinese name
Electrolytic method
Foreign name
Electrolytic process
Pinyin
diàn jiě fǎ
Discipline
Chemistry
Definition
Method of oxidation-reduction reaction with current
The principle of electrolytic preparation of metal powder is as follows:electrolyte solutionDirect current is applied to generate the migration of positive and negative ions. Positive ions move to the cathode, and negative ions move to the anode. Oxidation reaction occurs on the anode, and reduction reaction occurs on the cathode. The metal positive ions in the electrolyte solution are reduced at the cathode and deposited on the cathode plate.This is the basic process of electrolysis.Therefore, electrolysis is a process of realizing chemical reaction with the help of electric current, and also a process of transforming electric energy into chemical energy.[1]
Electrolytic process
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With CuCltwoElectrolysis is an example to illustrate the process of electrolysis.
CuCltwoyesStrong electrolyteIt is easily soluble in water and in aqueous solutionionizationGenerate Cu2+And Cl-。
CuCltwo=Cu2++Cl-
Before power on, Cu2+And Cl-Moving freely in the water;After electrification, these free moving ions, under the action of electric field, change to directional movement.Positively charged Cu in solution2+Moving towards the cathode, the negatively charged chloride ion moves towards the anode.At the cathode, copper ions obtain electrons and are reduced to copper atoms to cover the cathode;At the anode, chlorine ions lose electrons and are oxidized into chlorine atoms, which combine in pairs to form chlorine molecules and are released from the anode.
Cathode: Cu2++2e-=Cu
Anode: 2Cl-－2e-= Cltwo↑
Electrolytic CuCltwoChemical reaction equation of solution: CuCltwo=Cu+Cltwo↑ (electrolysis)
Narration aboveCupric chlorideIn the process of electrolysis, there is no mention of H in the solution+And OH-In fact, H+And OH-Although few, they do exist, but they do not participate in the electrode reaction.That is to say, in the copper chloride solution, Cu is removed2+And Cl-Besides, there is H+And OH-During electrolysis, the ions moving to the cathode are Cu2+And H+, because Cu2+Ratio H+Easy to get electrons, so Cu2+Electrons precipitate copper on the cathode.Ions moving to anode include OH-And Cl-, because under such experimental conditions, Cl-Ratio OH-It is easier to lose electrons, so Cl-Loss of electrons on anode, generationchlorine。
Analysis steps
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① Analyze the composition of electrolyte aqueous solution, find the total ions and divide them into two groups: anion and cation;
② Discharge the discharge sequence of the anion and cation respectively, and write the discharge sequence of theElectrode reaction formula；
③ Combine two electrode reaction equations to get the total amount of electrolytic reactionChemical equationorIonic equation。
Discharge sequence
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① The process in which the cation gains electrons or the anion loses electrons, thus reducing the number of charges carried by the ion, is also called discharge.
② Electrodes made of graphite, gold, platinum and other materials with weak reducibility are called inert electrodes, because they do not undergo chemical reaction under normal electrification conditions.Electrodes made of iron, zinc, copper, silver and other materials with strong reducibility are also called active electrodes. When they are used as anodes of electrolytic cells, they occur before other materialsoxidation reaction 。
③ Under general electrolysis conditions, when the aqueous solution contains multiple cations, their discharge sequence on the cathode is: Ag+>Hg2+>Fe3+>Cu2+>Pb2+>Sn2+>Fe2+>Zn2+>H+>Al3+>Mg2+>Na+>Ca2+>K+；When the aqueous solution contains multiple anions, the discharge sequence on their inert anode is: S2->I->Br->Cl->OH->Oxyate>F-。[2]
purpose
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Electrolysis is widely used inmetallurgical industry Such as extracting metals from ores or compounds (electrolytic metallurgy) or purifying metals (electrolytic purification), and depositing metals from solutions（electroplate)。
Metallic sodiumAnd chlorine are generated by electrolytic dissolving sodium chloride;Electrolysis of sodium chloride aqueous solution will producesodium hydroxideandchlorine。Electrolytic waterHydrogen and oxygen are produced.Water electrolysis is to decompose water into H under the action of external electric fieldtwo(g) And Otwo（g）；The molten fluoride can be oxidized to simple fluorine on the anode, and the molten lithium salt can be reduced to metallic lithium on the cathode;Smelting of many non-ferrous metals (such as sodium, potassium, magnesium, aluminum, etc.) and rare metals (such as zirconium, hafnium, etc.) and refining of metals (such as copper, zinc, lead, etc.), basic chemical products (such as hydrogen, oxygen, caustic sodaPotassium chlorate、hydrogen peroxide, acetonitrile, etc.), electroplatingElectropolishing、anodic oxidation And so on are achieved through electrolysis.
Rules of electrolytic products
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Sixteen word tips:
Yin gains and yang loses: During electrolysis, the cathode gets electrons, and a reduction reaction occurs; the anode loses electrons, and an oxidation reaction occurs;
Yin essence and Yang crude: In the process of refining copper, the cathode uses refined copper, and the anode uses crude copper. Finally, the anode gradually dissolves, andAnode slime；
Anion base cation acid: After electrolytic reaction, the oxygen containing salts of inactive metals will generate acid at the anode, while the oxygen free salts of active metals will generate alkali at the cathode;
Yin solidifies yang qi: After electrolytic reaction, the cathode produces solid and reducing gas, while the anode produces strong oxidizing gas.
