Chapter 5 Electrolysis PDF

# Chapter 5 Electrolysis ## Syllabus - Electrolytes & Non-electrolytes - Definitions & Examples - Substances containing molecules only, ions only, both molecules & ions - Examples relating their composition with their behaviour as strong & weak electrolytes as well as non-electrolytes. - Ex...

# Chapter 5 Electrolysis ## Syllabus - Electrolytes & Non-electrolytes - Definitions & Examples - Substances containing molecules only, ions only, both molecules & ions - Examples relating their composition with their behaviour as strong & weak electrolytes as well as non-electrolytes. - Explanation of electrolysis. Effects of anion, cation, oxidation & reduction (on the basis of loss & gain of electrons) - An elementary study of the migration of ions. - Influence of the electrochemical series. - Discharge of ions. Reference to the electrochemical series indicating the tendency of metals, e.g. Na, Mg, Fe, Cu, to be discharged. - Illustrated by the electrolysis of: - Molten lead bromide - Acidified water with platinum electrodes - Aqueous copper (II) sulphate with copper electrodes; electron transfer at the electrode. - The above electrolytic processes can be studied in terms of electrolyte used, electrodes used, including the anode reaction, cathode reaction, use of selective discharge theory, wherever applicable. - Applications of electrolysis: - Electroplating with nickel and silver, choice of electrolyte for electroplating - Electro refining of copper. ## Introduction - Electrolysis - The word 'electrolysis' can be split into electrolysis [meaning - electricity i.e. flow of electrons] & lysis [meaning - pertaining to decomposition]. - Electrolytes & non-electrolytes - Compounds which conduct electricity when dissolved in water or in the molten state are called electrolytes, e.g. NaCl, CuSO4, ect. while those which do not conduct electricity are called non-electrolytes. - **Electrolysis - Electrolytic Cell:** - A non-conducting vessel containing the electrolyte (in aq. or fused state). - **Anode:** Electrode connected to the positive terminal of the battery. - **Cathode:** Electrode connected to the negative terminal of the battery. - When the switch is 'on' the electrolyte dissociating. Current remaining the same the glow on the bulb indicates whether the electrolyte is: - Strong electrolyte - by bright glow of the bulb - Weak electrolyte - by dim glow of the bulb - Non-electrolyte - when bulb does not glow. ## Terms Involved in Electrolysis **1. Electrolysis**: - Decomposition of a chemical compound (electrolyte) in the aqueous or fused (molten) state by the passage of a direct electric current resulting in discharge of ions - as neutral atoms - at the respective electrodes. - Decomposition of electrolyte - in aq. or fused state by passage of electric current - NaCl (electrolyte) Na1+ (cation) + C11- (anion) - Discharge of ions - as neutral atoms at the respective electrodes - At cathode: Na1+ + 1e- → Na (neutral atom) - reduction reaction - negative electrode - At anode : C11- - 1e- → Cl - oxidation reaction - positive electrode - Electrolysis involves - a chemical change and is a Redox reaction (oxidation and reduction) **2. Electrolytes:** - Chemical compounds which conduct electricity in the fused or in aq. solution state and undergo chemical decomposition due to the flow of current through it. - Electrolytes - are ionic compounds - **Particles in electrolytes**: - Ions only or Ions & molecules only - Examples: - Acids - dil. HCl, HNO3, H2SO4 - Alkalis - KOH, NaOH solutions - Ionic salts - PbBr2 (molten), CuSO4 (aq.) **3. Strong electrolytes:** - Electrolytes which allow - a large amount of electricity to flow through them and hence are good conductors of electricity. - Strong electrolytes are - almost completely dissociated in fused or aqueous solution state. - **Particles in strong electrolytes:** - Mainly ions only. - Examples - generally all strong acids and bases and most salts of strong acids - Acids - dil. HCl, H2SO4, HNO3, HBr, HI - Bases - NaOH, KOH, LiOH solns. - Salts - NaCl (KCI), Na2SO4, NaNO3, CuCl2, PbSO4, Pb(NO3)2, PbBr2, AgI aq. solns. - (Salts in solid state are – non-electrolytes.) - (Electricity is conducted in an acid soln. by ions.) **4. Weak Electrolytes** - Electrolytes which allow small amounts of electricity to flow through them and hence are poor conductors of electricity. - Weak electrolytes are partially dissociated in fused or aqueous solution state. - **Particles in weak electrolytes** - Ions and unionized molecules. - Examples - generally all weak acids and bases and most salts of weak acids. - Acids - Carbonic, acetic, Oxalic, formic. - Bases - NH4OH, Ca(OH)2, Mg(OH)2 - Salts - Sodium – carbonate, bicarbonate, oxalate and formate aq. solns. **5. Non-electrolytes** - Chemical compounds which do not conduct electricity in the fused or aq. soln. state and do not undergo chemical decomposition due to the flow of current through it. - Non-electrolytes - are covalent compounds. - **Particles in non-electrolytes**: - Molecules only - Examples: - Pure or distilled water, Alcohol, Kerosene, Carbon disulphide, liq. carbon tetrachloride (CCl4), sucrose, glucose, sugar solution. **6. Ions** - Atoms or groups of atoms which carry a positive or a negative charge and become free and mobile when an electric current is passed through an aq. solution of a chemical compound. - Depending on the type of electric charge (+ve or -ve) carried by an ion - an ion is further classified into anions and cations. **7. Anions** - Negatively charged ions. - Migrate to the anode during electrolysis and are discharged at it. - Donate or lose electrons to the anode (oxidation process) and get - oxidised to neutral atoms. - Anode: C11- - 1e- → Cl (neutral atom) - (anion) **8. Cations** - Positively charged ions. - Migrate to the cathode during electrolysis and are discharged at it. - Accept or gain electrons from the cathode (reduction process) and get - reduced to neutral atoms. - Cathode: Na1+ + 1e- → Na (neutral atom) - (cation) ## Mechanism - Of Electrolysis - The process or mechanism of electrolysis was first explained by a Swedish chemist Avante Arrhenius in 1887. The main findings or postulates of his theory are as follows: - An electrolyte on dissolving in water dissociates into free cations (+ve ions) & anions (-ve ions) and allows the flow of electric current through it. - The degree of dissociation is the extent to which an electrolyte dissociates or breaks up, into ions. - All ions carry an electric charge and are responsible for the flow of current through the solution. The amount of electricity conducted by the electrolyte depends upon the concentration of the ions in the solution. - The number of positive charges on the ions equals the number of negative charges and thus the solution is in electrolytic equilibrium (an equilibrium is also established between the ions produced and unionized molecules). ### Characteristics - Of Electrolysis - The passage of electricity through an electrolyte causes the metallic ions (cations) to migrate towards the cathode and non-metallic ions (anions) to migrate towards the anode. - The preferential discharge of the ions depends on its position in the electrochemical series. - The number of electrons gained by the anode - is equal to the number of electrons donated by the cathode. - The products of electrolysis are formed at the anode and cathode itself since the exchange of electrons takes place only at the surface of the electrodes. - Only hydrogen gas and metals are liberated at the cathode and are hence called - electropositive elements. - Only non-metals are liberated at the anode and are called – electronegative elements. ### Electrolytic Dissociation - The Term : - The process due to which an ionic compound in the fused (molten) state or in aqueous solution state dissociates into ions by passage of electric current through it is called – electrolytic dissociation. ### Comparison between - Electrolytic Dissociation & Ionisation | | Electrolytic Dissociation | Ionisation | |:----------|:-----------------------------------------------|:--------------------------------------------------| | | Takes place in - electrovalent compounds | Takes place in - covalent compounds | | | Involves - separation of ions | Involves - formation of charged ions | | | of the ions which are already present | from the molecules which are | | | in an ionic compound. | not in the ionic state. | | | PbBr2 →Pb2+ + 2Br1- (ionic) | HCl (aq.) →H1+ + C11- (covalent) | | | | Ionisation may also involve atoms changing | | | | into ions (eg. Mg →Mg2+ + 2e- (ED) | ## Mechanism - Of Electrolysis (Contd.) ### Electrolytic Dissociation - Of Ionic Compounds [NaCl] - Solid sodium chloride is a – non-electrolyte & does not allow electricity to pass through it, but dissociates in the – molten (fused) or in aqueous solution state. (Thus sodium chloride will conduct electricity only in fused or aqueous solution state). **a) In the molten state (fused)** - Ionic compounds (eg. NaCl) contain - positively charged metallic ions (Na1+) & negatively charged non-metallic ions (C11-). - These ions are not free but held together by strong electrostatic force of attraction. Due to this an ionic compound in the solid state is a bad conductor of electricity since free ions are essential for conducting electricity. - When an ionic compound is heated strongly - the ions gain kinetic energy and break lose and move freely. - The molten solution then becomes a – good conductor of electricity. - **Dissociation of sodium chloride - In the molten state** - Electrostatic force of attraction - Heat - Na1+ + C11- - Na1+ + C11- - *Sodium chloride in solid state* - *Free ions formed in molten state* **b) In the aqueous solution state ** - Water is a - polar solvent and exhibits - charge distribution in its molecule. - In water each hydrogen atom develops a slight positive charge while the oxygen atom develops a slight negative charge. - When sodium chloride is dissolved in water it dissociates into sodium ions (Na1+) and chloride ions (C11-) which move freely in solution. - This is due to the fact that the slightly negatively charged oxygen atoms of water exert a pull on the positively charged sodium ion.). A similar pull is executed by the slightly positively charged hydrogen atoms of the water on the negatively charged chloride ions. Thus, Sodium and chloride ions become free in solution. - **Dissociation of sodium chloride - In aqueous solution** - Water molecule polar solvent - Na1+ + C11- - (Sodium chloride in solid state) - Na1+ + C11- - (Free ions formed in aqueous solution state) ### Ionisation – Of Covalent Compounds [HCI] - Polar covalent compounds (eg. ammonia, hydrogen chloride) - are non-electrolytes in the gaseous state, but ionise in aqueous solution state. - Hydrogen chloride in the gaseous state or in the pure liquid state - is unionized and does not conduct an electric current. - Hydrogen chloride is however - polar covalent in nature i.e. shows charge distribution in its molecule such that the hydrogen atom has a slight positive charge & chlorine atom a slight negative charge. - When hydrogen chloride is added to water - a polar solvent - the slightly negatively charged oxygen atom of the water exerts an electrostatic pull on positively charged hydrogen ion of HCl. Thus H+ ions combine with the water, forming hydronium ions (H3O+) and the residual chloride ions remain in solution. (Hence ammonia or hydrogen chloride in gaseous or pure liquid state does not conduct electricity, but conducts electricity when dissolved in water) - **Ionisation of hydrogen chloride molecule - In aqueous solution** - HS+CIS- (Hydrogen chloride) - H+ + Cl- (Hydrogen ion + Chloride ion) - (Polar covalent compound) - (Ionisation) - Water H+ + H2O → H3O+ - Hydronium ion - (Polar solvent) ## Comparison between - Metallic conduction & Electrolytic conduction | | Metal [eg, Cu] | Electrolyte [eg, CuSO4] | |--------------|:------------------------------------------------------|:--------------------------------------------------------------------------------------------------------------------------| | Flow of electricity | Flow of electrons | Flow of ions | | | Which have negligible mass. | Which are denser compared to electrons. | | | There is no decomposition of the | There is decomposition of the | | | parent metal and thus the | electrolytic solution and thus the | | | Chemical properties of metal are intact. | chemical properties of electrolyte are altered. | | | Metals are - | Electrolytes are- | | | good conductors of electricity | good conductors of electricity | | | in the solid state and in the molten state. | in aq. soln. or molten state but not in solid state. | | | During metallic conduction there is | During electrolytic conduction there is | | | no transfer of matter. | transfer of ions. | | | The flow of electricity only produces heat | The flow of electricity decomposes the | | | energy & no new products are formed. | electrolyte & new products are formed. | Copper metal - is thus a good conductor of electricity - but is a non-electrolyte, since - it does not undergo chemical decomposition due to flow of electric current through it. Copper (II) sulphate on the other hand is an electrolyte – since it decomposes on passage of electric current forming copper ions and sulphate ions. The Cu2+ ions are discharged at the cathode as Cu metal - when copper electrodes are used during electrolysis. ## Acids, Bases, and Salts - As electrolytes **Acids, Bases, and Salts**: Acids, bases (alkalis) and salts when dissolved in water or in the fused state (salts) dissociate into - free mobile ions and can be classified as (strong or weak electrolytes - depending on the degree of dissociation. **Strong electrolytes**: Compounds which in the fused or in the aqueous solution state are almost completely dissociated and are good conductors of electricity are called - strong electrolytes. **Weak electrolytes**: Compounds which in the fused or in the aqueous solution state are feebly or partially dissociated and are poor conductors of electricity are called – weak electrolytes. ### Classification of acids, bases and salts into – strong and weak electrolytes | | Acids | Bases (alkalis) | Salts | |:---|:---------------------------------------|:---------------------------------------------|:---------------------------------------------| | | Mineral acids ionise - | Bases ionise - | Ionic salts ionise - | | | on dissolution in | in fused or in aq. soln. | in fused or in aq. soln. | | | water | state | state | | | [Furnish - | [Furnish - | [Furnish - positive ions other | | | H+ ions in solution] | OH- ions in solution] | than H+ and negative ions other | | | | | than OH- ions] | | | **Strong electrolytes** | **Strong electrolytes** | **Strong electrolytes** | | | Hydrochloric acid | Potassium hydroxide | Lead bromide | | | HCI - H1+ + Cl1− (aq.) | KOH = K1+ + OH1- (aq.) | PbBr2 Pb2+ + 2Br1− (molten) | | | Nitric acid | Sodium hydroxide | Copper chloride | | | HNO3 = H1+ + NO31− (aq.) | NaOH Na1+ + OH1− (aq.) | CuCl2 Cu2+ + 2C11- | | | Sulphuric acid | Lithium hydroxide | Silver nitrate | | | H2SO4 2H1+ + SO42− (aq.) | LiOH 2 Li1+ + OH1− (aq.) | AgNO3 Ag1+ + NO31− (aq.) | | | | | | | | **Weak electrolytes** | **Weak electrolytes** | **Weak electrolytes** | | | Acetic acid | Calcium hydroxide | Sodium carbonate | | | CH3COOH CH3COO− + H1+ (aq.) | Ca(OH)2 Ca2+ + 2OH1− (aq.) | Na2CO3 2Na1+ + CO32− (aq.) | | | Formic acid | Magnesium hydroxide | Potassium bicarbonate | | | H:COOH HCOO1− + H1+ (aq.) | Mg(OH)2 Mg2+ + 2OH1− (aq.) | KHCO3 K1+ + HCO31− (aq.) | | | Carbonic acid | Ammonium hydroxide | Lead acetate | | | H2CO3 2H1+ + CO32− (aq.) | NH4OH = NH4+ + OH- (aq.) | (CH3COO)2Pb2CH3COO- + Pb2+ (aq.) | ## Applications - Of Electrolysis - The main applications of electrolysis are: - Electroplating - of metals (Deposition of superior metal on base) - Electro-refining or purification - of metals - Extraction - of metals i.e. electrometallurgy (dealt in metallurgy) ### 1. Electroplating - Of Metals - Electroplating is the electrolytic process of deposition of a superior metal (eg. nickel, silver, chromium, gold) on the surface of a baser metal or article (eg. iron, copper, brass). #### Reasons for Electroplating - Prevents corrosion or rusting - of the base metal. - Example: Base metal iron plated with - nickel or chromium. - Makes the article attractive - and gives it an expensive appearance. - Example: A brass article plated with - silver or gold. #### Conditions - For Electroplating | Condition | Reason | |:------------------------------------------------|:--------------------------------------------------------------------------------------------------------------------| | The article to be electroplated | During electrolytic reaction - | | is always placed at the - cathode. | the metal is always deposited at the cathode – by gain of electrons. | | The metal to be plated on the | The metal anode continuously dissolves as ions in solution and is hence - | | article is always made the – anode. | replaced periodically. | | It has to be replaced periodically. | | | The electrolyte – | The electrolyte dissociates - | | must contain – ions of the metal | into ionic of the metal which migrate towards the cathode and are deposited | | used for plating on the article. | neutral metallic atoms on the cathode (article). | | (metal to be electroplated with silver - | | | must contain – ions of the metal silver) | | | A low current and for a- | Higher current causes – | | longer time should be used. | uneven deposition of the metal. Low current for a longer time - in smooth, firm, uniform & long lasting deposit. | | A direct current and not A.C. | A.C. current causes - discharge and ionisation to alternate at the cathode. Thus giving no effective coating. | | current should be used. | | | Quite expensive | | ## Electroplating - Of Metals (Contd.) ### a) Electroplating with - NICKEL - Anode: Block of nickel, NiSO4 soln. - Cathode: Article to be plated. - **Electroplating of an article with nickel:** -1. **Electrolyte:** Aqueous soln. of - nickel sulphate- NiSO4 -2. **Nature of electrode** - Cathode: Cleaned article to be electroplated. - Anode: Active electrode, Plate or block of nickel metal. -3. **Electrode reactions** - Dissociation of aq. nickel sulphate - NiSO4 = Ni2+ + SO42- - H2O = H1+ + OH1- - **Reaction at cathode** - Ni2+ + 2e- → Ni (deposited) - Ni2+ ions move towards the cathode and are discharged as - neutral Ni atoms - by gain of electrons (in preference to H1+). - Thus nickel is - deposited on the article (cathode). - **Reaction at anode** - Ni -2e- → Ni2+ (cation) - SO42- and OH1- ions migrate to the anode but neither are discharged. - Instead the nickel anode - loses electrons to give – Ni2+ ions in soln. - (Nature of electrode - Ni active electrode). - Hence anode - diminishes in mass. - (Product at anode - Nil (Ni2+ ions formed). ### b) Electroplating with - SILVER - Anode: Block of silver, Na[Ag(CN)2] soln. - Cathode: Article to be plated. - **Electroplating of an article with silver:** -1. **Electrolyte:** Aq. soln. of sodium silver cyanide - Na[Ag(CN)2] i.e. sodium argentocyanide. -2. **Nature of electrode** - Cathode: Cleaned article to be electroplated. - Anode: Active electrode, Plate or block of silver metal. -3. **Electrode reactions** - Dissociation of aq. sodium silver cyanide - Na[Ag(CN)2] Na1+ + Ag1+ + 2CN1- - H2O = H1+ + OH1- - **Reaction at cathode** - Ag1++ 1e → Ag (deposited) - Ag1+ ions move towards the cathode and are discharged as - neutral Ag atoms - by gain of electrons (in preference to Na1+, H1+). - Thus silver is - deposited on the article (cathode). - **Reaction at anode** - Ag -1e- → Ag1+ (cation) - CN1- and OH1- ions migrate to the anode but neither are discharged. - Instead the silver anode - loses electrons to give – Ag1+ ions in soln. - (Nature of electrode - Ag active electrode). - Hence anode – diminishes in mass. - (Product at anode - Nil (Ag1+ ions formed). ## Electrorefining - Of Metals i.e. purification of metals - Electrorefining - is a process by which metals containing impurities are purified electrolytically - to give a pure metal. - The term 'refining' means to – make pure and 'electro' – the method employed to make the metal pure i.e. by electrolysis. - **Electro-refining of - COPPER** - 1. **Electrolyte:** Aqueous copper sulphate solution (acidified) - 2. **Nature of electrode**: - Cathode: Pure thin sheet of copper. - Anode: Impure block of copper. - 3. **Electrode reaction** - Dissociation of aqueous copper sulphate - CuSO4 → Cu2+ + SO42- - H2O → H1+ + OH1- - **Reaction at cathode** - Cu2+ + 2e- → Cu (deposited) - Cu2+ ions are discharged at the cathode as neutral copper atoms. - Thus pure copper deposited on the thin sheet of pure copper placed at the cathode. - **Reaction at anode** [Cu – active electrode] - Cu - 2e- → Cu2+ (cation) - SO42- and OH1- - migrate to the anode but – neither are discharged. - Instead the copper anode – itself loses electrons to give Cu2+ ions in solution. - Hence anode diminishes in mass. - The impure block of copper [anode] gets used up and the impurities settle down. - The pure copper metal dissolves out from the copper anode (impure copper block) and the Cu2+ ions formed in solution at the anode) are deposited at the cathode i.e. on the thin pure sheet of copper (by gaining electrons). - The impurities present in impure copper anode settle down as anode mud or slime which contains insoluble impurities like - gold and silver. - Impurities such as – iron, zinc, etc (higher in the electrochemical series) ionise and dissolve in the electrolytic copper sulphate solution. - Metals generally refined by – electrolysis. - Metals which are extracted by electrolysis i.e. highly electropositive metals are already deposited at the cathode in the pure state & hence need not be refined further. Zinc, lead, copper, mercury and silver - are thus generally refined by electrolysis. ## Electrometallurgy-process of extraction of metals by electrolysis. [Reference] - Method of extraction of metals - depends on position of the metal - in the activity series. | Activity series | Method of extraction of the metal | Examples | |:--------------|:-------------------------------------------------------------------------|:---------------------------------------------------------------------------------------------------------------------------------| | K | BY ELECTROLYSIS - of their fused salts | 1. Electrolyte: fused sodium chloride. NaCI = Na1+ + C11- | | | For metals - higher in electrochemical series. | Cathode: Na1+ + 1e- → Na | | | Their oxides are - highly stable. | Anode: C11- - 1e-→ Cl | | | Metal has - strong affinity for oxygen. | Cl + Cl → Cl2 | | | On electrolysis - metal is deposited at the cathode. | | | | Metals generally extracted by electrolysis are - K, Na, Ca, Mg, Al. | 2. Electrolyte: fused calcium chloride. CaCl2 = Ca2+ + 2C11- | | | | Cathode: Ca2+ + 2e- → Ca Anode: 2C11- - 2e- → 2C1 [Cl2] | | | | 3. Electrolyte: fused alumina. Al2O3 = 2A13+ + 302- | | Na | | Cathode: 2A13+ + 6e- = 2A1 Anode: 302- - 6e- = 3[0] | | Ca | | 3[0] + 3[0] = 3O2 CuO + C → Cu + CO | | Mg | eg. Al2O3 is a highly stable oxide & Al has a strong affinity for oxygen | | | | hence conventional reducing agents like - C, CO & H2 cannot reduce | | | | Al2O3 to Al & hence Al is extracted by electrolysis. | | | | | Δ | | | | 2HgO → 2Hg + O2 | | Al | By using - Reducing agents - C, CO, H2 | | | | Their oxides are - less stable. | | | Zn | | | | Fe | - Reducing agents - reduce metallic oxide to metal. | | | Pb | | | | [H] | | | | Cu | By - Thermal decomposition | | | | Their oxides are - least stable. | | | Hg | - Heat alone - can reduce metallic oxide to metal. | | | Ag | | | #### Summary of – Electrode reactions | | MOLTEN LEAD BROMIDE | ACIDIFIED WATER | COPPER (II) SULPHATE | |--------------|:---------------------------------:|:----------------------------------------------------|------------------------------------------------------------------------------| | 1. Electrolyte | PbBr2 (molten) | H2O (H2SO4) | CuSO4 (aq.) | | 2. Electrode | Inert-graphite | Inert-platinum | Active - copper | | 3. Electrode | | H2SO4 → 2H1+ + SO42- | CuSO4 → Cu2+ + SO42 - | | reaction | PbBr2 → Pb2+ + 2Br1- | H2O → H+ + OH- | H2O = H+ + OH1- | | | | H1+ + 1e- → H x 4 | Cu2+ + 2e- → Cu | | | | 2H + 2H → 2H2 | | | 4. Cathode reaction | Pb2+ + 2e- → Pb | Hydrogen gas (2 vols.) | Copper metal | | 5. Anode reaction | Br1- - 1e → Br | OH1- - 1e- → OH x 4 | Cu - 2e- → Cu2+ | | | | 4OH ← 2H2O + O2 | | | | | Oxygen gas (1 vol.) | Nil [Cu2+ ions] | | 6. Product | Lead metal | | | | | Bromine vapours | | | #### SUMMARY OF - Applications of electrolysis | | NICKEL ELECTROLATING | SILVER ELECTROLATING | ELECTROREFINING - of | |----------|:---------------------------------|:----------------------------------------------------|:----------------------------------------| | 1. Electrolyte | NiSO4 (aq. soln) | Na [Ag(CN)2] (aq. soln) | CuSO4 [acidified aq. soln.] | | 2. Electrode | | | | | | Cathode used | Article to be plated | Thick block to be plated | Pure thin sheet of Cu | | | Anode used | Thick block of Ni | Thick block of silver | Impure block of Cu | | 3. Electrode | | | | | reaction | NiSO4 → Ni2+ + SO42- | Na[Ag(CN)2] = Na1+ + Ag1++ 2CN1- | CuSO4 → Cu2+ + SO42- | | 4. Cathode | | | | | reaction | Ni2+ + 2e- → Ni | Ag1+ + 1e- → Ag | Cu2+ + 2e- → Cu | | | | | | | 5. Anode | Ni - 2e- → Ni2+ | Ag - 1e- → Ag1+ | Cu - 2e- → Cu2+ | | reaction | | | | 121