8. Electrochemistry
8.4. Electrolysis
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The reaction between copper and chlorine
Copper reacts with chlorine gas and forms cupric chloride, CuCl2.
Cu(s) + Cl2(g) → CuCl2(s)
- The reaction is spontaneous and exothermic.
- The electrons perform work.
- What happens if we run the reaction ”backwards”?
- Electrolysis = splitting (lysis) with the help of electricity.
Electrolysis of cupric chloride, CuCl2
Electrolysis of cupric chloride.
Cathode reaction (reduction)
- Electrons are pushed into the cathode
- Aqueous copper ions are reduced to solid copper:
- Cu2+(aq) + 2e– → Cu(s)
Anode reaction (oxidation)
- Electron shortage
- Chloride ions pulled towards the anode, oxidized to chlorine gas:
- Cl–(aq) → Cl2(g) + 2e–
Production of sodium hydroxide
Sodium hydroxide is produced by electrolysis of sodium chloride.
Anode reaction
Similar to the electrolysis of cupric chloride:
- Electron shortage in the anode
- Chloride ions pulled towards the anode, oxidized to chlorine gas:
- Cl–(aq) → Cl2(g) + 2e–
Cathode reaction
Two possibilities:
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1. Na+(aq) + e– → Na(s) |
\(e^0_{\text{Na}} = -2.71 \text{V}\) |
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2. 2H2O + 2e– → H2(g) + 2OH–(aq) |
\(e^0_{\text{H}_2\text{O}} = -0.83 \text{V}\) |
It can only be the second one, because:
- Any sodium atoms that form would immediately react with water:
- 2Na(s) + 2H2O → 2Na+(aq) + 2OH–(aq) + H2(g)
- The standard electrode potential for water is greater than the electrod potential for sodium, making the water a stronger oxidizing agent.
- \(e^0_{\text{H}_2\text{O}} > e^0_{\text{Na}}\) ⇒ Reaction 2 takes place rather than reaction 1.
Total reaction
2NaCl(aq) + 2H2O → Cl2(g) + H2(g) + 2NaOH(aq)
The concentrated sodium hydroxide solution is let out through a pipe.
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Contents
- 1. States of Matter. The Atom and the Periodic Table
- 1.1. Matter. States of Matter
- 1.2. Elements and Chemical Compounds. Pure Substances and Mixtures
- 1.3. The Birth of Chemistry
- 1.4. Atomic Theory. The Atomic Model
- 1.5. Atomic Number, Mass Number, and Atomic Mass
- 1.6. Electron Configurations
- 1.7. Beyond Bohr's Atomic Model
- 1.8. Redox Reactions
- 1.9. The Structure of the Periodic Table
- 1.10. The Noble Gases
- 1.11. The Alkali Metals and the Halogens
- 1.12. The Alkaline Earth Metals and the Oxygen Group
- 1.13. A Few of the Elements in Group 13, 14, and 15
- 2. Chemical Calculations
- 2.1. Physical Quantity, Magnitude, and Units
- 2.2. Atomic Mass, Molecular Mass, and Unit Mass
- 2.3. Amount of Substance, Molar Mass, and Mass
- 2.4. Stoichiometry. Conservation of mass
- 2.5. Water of Crystallization
- 2.6. Calculating the Formula of a Chemical Compound
- 2.7. From Empirical to Molecular Formulas
- 2.8. Equivalent Amounts of Substance and Masses
- 2.9. Gases and Pressure
- 2.10. Concentrations
- 2.11. Dilutions
- 2.12. Yield
- 2.13. Limiting Reactants
- 3. Chemical Bonding
- 3.1. How Ionic Compounds are Formed
- 3.2. Precipitations
- 3.3. Names and Formulas of Ionic Compounds
- 3.4. Ionic Bonds
- 3.5. Properties of Ionic Compounds
- 3.6. Metal Bonding
- 3.7. Covalent Bonds
- 3.8. Polar Covalent Bonding
- 3.9. Dipoles. Polar and non-polar Molecules
- 3.10. The VSEPR Theory
- 3.11. Hydrogen Bonding. The Peculiar Water
- 3.12. Equals Solves Equal
- 3.13. Solubility of Gases in Water
- 3.14. Solubility of Salts in Water
- 4. Thermochemistry
- 5. Chemical Equilibrium
- 5.1. Reaction Rates
- 5.2. The Law of Mass Action
- 5.3. Calculations on Chemical Equilibrium
- 5.4. Heterogenous Equilibria. Solubility Product
- 5.5. Is the System at Equilibrium? The Reaction Quotient Q
- 5.6. Changing the Concentrations in a System in Equilibrium.
- 5.7. Diluting or Compressing Systems in Equilibrium, or Changing the Temperature
- 6. Acids and bases
- 7. Oxidation and Reduction
- 8. Electrochemistry
- 9. Organic Chemistry
- 9.1. Alkanes
- 9.2. Chain Isomers. Nomenclature
- 9.3. Haloalkanes
- 9.4. Nucleophilic Substitution
- 9.5. Alkenes
- 9.6. Electrophilic Addition. Markovnikov’s Rule
- 9.7. Elimination
- 9.8. Alkynes
- 9.9. Arenes and Aromatic Compounds
- 9.10. Alcohols
- 9.11. Oxidation of Alcohols
- 9.12. Aldehydes and Ketones
- 9.13. Thiols and Disulfides
- 9.14. Ethers
- 9.15. Amines
- 9.16. Nitro Compounds and Organic Nitrates
- 9.17. Carboxylic Acids
- 9.18. More on Carboxylic Acids
- 9.19. Stereoisomerism
- 9.20. Esters
- 9.21. Lipids
- 9.22. Mono-, Oligo-, and Polysaccharides
- 9.23. Amino Acids
- 9.24. Nucleotides
- 10. Biochemistry
- 10.1. Proteins
- 10.2. Enzymes
- 10.3. Catabolic Processes
- 10.4. Carrier Molecules
- 10.5. Glycolysis
- 10.6. Beta-oxidation
- 10.7. The Citric Acid Cycle
- 10.8. The Metabolism of Amino Acids
- 10.9. The Electron Transport Chain
- 10.10. Anabolic Processes
- 10.11. Gluconeogenesis and Fatty Acid Synthesis
- 10.12. DNA: Structure and Function
- 11. Analytical chemistry