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Science C3 Topic 3

GCSE edexcel further additional chemistry: electrolytic processes

QuestionAnswer
What is electrolysis? Electrolysis is the process in which electrical energy from a DC supply decomposes compounds
What is an electrolyte and what state must it be in? An electrolyte is an ionic substance in a molten state or dissolved in water - since the ions can move freely and conduct the charge, electrolysis can occur
Which ions migrate to which electrodes? * Cations are positive ions, so migrate to the negatively charged cathode * Anions are negative ions, so migrate to the positively charged anode
What is reduction, which electrode does it occur at? Reduction is when a positive ion gains electrons, forming a neutral atom - occurs at the cathode (electrons are transferred from the electrode to the cations)
What is oxidation, which electrode does it occur at? Oxidation is when a negative ion loses electrons, forming a neutral atom - occurs at the anode
What are half-equations? Half equations show the reactions that occur at each electrode
Write the electrolysis of magnesium bromide and sodium chloride as half equations NaCl Anode: 2Cl- -> Cl2 + 2e- Cathode: Na+ + e- -> Na MgBr2 Anode: 2Br- -> Br2 + 2e- Cathode: Mg2+ + 2e- -> Mg
What are some uses of sodium and how is it produced? Produced by electrolysis of NaCl. Used in street lamps as the vapour gives out a bright yellow glow when an electric current is passed through. A coolant in nuclear reactors - transfers heat from core to the water which turns to steam + drives generators
What happens at the electrodes and what are the half-equations of the electrolysis of copper chloride solution? •Anode: chlorine ions are discharged (lose electrons) to give chlorine gas •2Cl- (aq) -> Cl2 (g) +2e- •Cathode: copper ions are discharged (gain electrons) •Cu2+ (aq) +2e- -> Cu (g)
What happens at the electrodes and what are the half-equations of the electrolysis of copper sulphate solution? •Anode: hydroxide ions are discharged (lose electrons) to form water and oxygen •4OH- (aq) -> 2H2O (l) + O2 (g) + 4e- •Cathode: copper ions are discharged (gain electrons) •Cu2+ (aq) +2e- -> Cu (g)
What happens at the electrodes and what are the half-equations of the electrolysis of sodium sulphate solution? •Anode: hydroxide ions are discharged (lose electrons) to form water and oxygen •4OH- (aq) -> 2H2O (l) + O2 (g) + 4e- •Cathode: hydrogen ions are discharged (gain electrons) to give hydrogen gas •Cu2+ (aq) +2e- -> Cu (g)
What happens at the electrodes, what is left over at the end, and what are the half-equations of the electrolysis of sodium chloride solution? •Anode: chlorine ions are discharged to give chlorine gas •2H+ (aq) +2e- -> H2 (g) •Cathode: hydrogen ions are discharged to give hydrogen gas •2H+ (aq) +2e- -> H2 (g) •Na+ (aq) and OH- (aq) ions are left forming a sodium hydroxide solution, NaOH (aq)
How is electrolysis used in the purification of copper? Anode = impure copper. Cathode = a sheet of pure copper. Electrolyte is copper sulphate solution. During electrolysis the copper atoms in anode lose 2 electrons & become copper ions- they dissolve in solution, migrate to cathode + deposited as pure copper
In the purification of copper, which electrode gains mass and which loses mass? The anode loses mass and the cathode gains mass
What happens to the impurities that were in the copper after it has been purified? The impurities from the anode are insoluble and form sludge which is collected as it may contain valuable metallic elements
What are the half-equations that occur during the purification of copper? *Anode: Cu (s) -> Cu2+ (aq) + 2e- *Cathode: Cu2+ (aq) + 2e- -> Cu (s)
What is electroplating? Electroplating is covering one metal with a thin layer of another metal, using electrolysis
What are the electrodes and the electrolyte when iron is being plated with silver? * The anode is the metal that will form the plating - silver * The cathode is the object to be plated - iron * The electrolyte contains ions of the metal that will form the plating - e.g. silver nitrate solution
How can the layer of plating be thickened? To form a thicker plating layer, increase the current or carry out electrolysis for a longer time period
Why might someone want to electroplate metals? improves resistance to corrosion, cosmetic purposes (silver or gold plating gives an attractive appearance and is cheaper than making the whole object out of the expensive metals)
What is galvanised steel? Galvanised steel is steel coated with zinc- the zinc protects the iron from rusting and forms a zinc oxide which has a similar colour to zinc, protecting both metals
How is sodium produced? Sodium is produced from the electrolysis of molten sodium chloride
Why does sodium have to be produced from a molten form? Because sodium chloride solution electrolysises to form hydrogen, which is a product of the water, rather than forming sodium, which is a product of the salt. This is because sodium is too reactive.
Created by: 11043