Electrolysis Practice

• A chemical change is when the properties of a substance are changed
• What is electrolysis?

  Using electricity to break down an ionic compound into elements
• Why must ionic compounds be liquid or dissolved in water for electrolysis to work?

  So ions can move and carry charge.
• Explain what happens at the cathode (negative electrode)?

  Positive ions (cations) are attracted and gain electrons in reduction.
• Explain what happens at the anode (positive electrode)?

  Negative ions (anions) are attracted and lose electrons in oxidation.
• At which electrode would Zn²+(aq) turn into Zn(s)?

  Negative electrode
• At which electrode would Cl⁻(aq) turn into Cl₂(g)?

  Positive electrode
• Complete the half equation: Al³⁺ + ___ → ____

  Al³⁺ + 3e⁻ → Al
• Complete the half equation: Cl⁻ → ____ + ____

  2Cl⁻ → Cl₂ + 2e⁻
• Complete the half equation: __O²⁻ → ____ +____

  2O²⁻ → O₂ + 4e⁻
• What will be the products for the electrolysis of molten iron bromide?

  Iron and Bromine
• What will be the products for the electrolysis of molten zinc oxide?

  Zinc and Oxygen
• What is the disadvantages of using electrolysis?

  Requires a large amount of electrical energy which is expensive
• Why is aluminium oxide mixed with cryolite when extracting aluminium?

  To lower the melting point
• What is produced at the anode and cathode in the electrolysis of aluminium oxide?

  Aluminium at the cathode and oxygen at the anode
• Why does the anode need to be replaced in the electrolysis of aluminium oxide?

  The oxygen reacts with the carbon electrode to produce carbon dioxide.
• Where does hydrogen come from in electrolysis of solutions?

  Water
• Where does Oxygen come from in electrolysis of solutions?

  Hydroxide ions from water
• When is hydrogen made at the negative electrode in solutions?

  If the metal is more reactive than hydrogen.
• When is oxygen made at the positive electrode in solutions?

  If the non-metal ion is a not a halide.
• Which two ions are involved in electrolysis when water is present?

  H+ ions and OH- ions.
• In the electrolysis of sodium chloride solution, what are the products?

  Chlorine gas, hydrogen gas and sodium hydroxide.
• In the electrolysis of sodium chloride solution why is hydrogen gas produced?

  Sodium is more reactive than hydrogen.
• In the electrolysis of sodium chloride solution why is chlorine gas produced?

  Chloride is a halide ion.
• In the electrolysis of sodium chloride solution why is sodium hydroxide produced?

  Left over sodium ions and hydroxide ions remain in the water.
• What is the half equation for the formation of hydrgen gas at the negative electrode?

  2H+ + 2e- --> H2
• What is the half equation for the formation of oxygen gas at the positive electrode?

  4OH- --> O2 + H2O + 4e-
• On an electrolysis diagram, what are the things that need to be labelled?

  Power supply, positive electrode, negative electrode, electrolyte or metal solution.
• Suggest two reasons why we should recycle aluminium drinks cans.

  Landfill problem

  Saves energy

   
• Explain why iodine has a low melting point

  Simple molecules with weak intermolecular forces
• The electrolyte contains cryolite. Explain why

  because it lowers the melting point so less energy is needed