Electrolysis

Electrolysis

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Electrolysis

Electrolysis means splitting up using electricity. Using Electricity to break down a substance. An electrolyte is the substance that is broken down by electrolysis.   Its all about turning ions into atoms. Gaining electrons is called Reduction and losing electrons is called Oxidation.Oxidation Is Loss, Reduction Is Gain OILRIGAt the electrodes, negative ions are oxidised at the anode, while positive ions are reduced at the cathode.Ionic compounds can only be electrolysed when they are molten or dissolved in water. Thats because their ions are then free to move and carry their charge to the electrodes. In electrolysis, the positive ions move to the cathode while negative ions move to the anode. When electrolysis happens in aqueous solution, the less reactive element, either hydrogen or the metal, is usually produced at the cathode. At the anode we often get oxygen gas given off from discharged hydroxide ions produced from water.

Electrolysis of CuCl : The negative (chloride) ions go to the Positive electrode, lose electrons and form Chlorine gas. The positive (copper) ions go to the Negative electrode, gain electrons and form Copper. Copper is formed at the negative electrode and Chlorine gas is formed at the positive electrode. You can test for Chlorine gas because it will turn litmus paper red because it’s acidic.

Aluminium:Aluminium is a reactive metal that has a low density but is strong. Aluminium ore is a bauxite Aluminium Bauxite is mixed with Cryolite to lower the melting point from 2500 → 850℃ It has to be molten for the ions to move.The high temperatures mean that a lot of energy is required so the plant will have its own power station.Extraction of Aluminium:Negative Electrode – Positive Al atoms are attracted to the negative electrode. They gain electrons and are reduced to form aluminium (atoms).Positive Electrode – Negative O  ions are attracted to the positive electrode. They lose electrons and are oxidised to form Oxygen. This reacts with the carbon electrode to form Carbon dioxide. - The carbon anodes need to be replaced regularly as they gradually burn away.

Extraction of Aluminium

Molten NaCl produces Na  + Cl  ions. NaCl solution (brine) produces Na  + Cl  + H  + OH When we electrolyse brine, the products depend on their reactivity. The more reactive ions stay in the solution. Na  + OH  →NaOH (alkaline turns universal indicator blue/ red litmus blue) What happens in the electrolysis of Brine? NaCl(aq) → Na  + Cl  + H  + OH Positive Electrode: The negative chloride ions are attracted to the positive electrode (anode). They lose electrons It Oxidises to form Chlorine Gas (molecules) 2Cl (aq) – 2e  → Cl (g)

Negative electrode: The positive Sodium ions are attracted to the negative electrode (cathode). They gain electrons It reduces to form Sodium (atoms). Na  + e  → Na(s) An electrolyte is a substance that is broken down by electrolysis. Hydrogen is used in the production of margarine.Sodium hydroxide is used to make bleach, paper and soap. 

Electrolysis of Brine

Electroplating

Test for Chlorine: Red litmus paper → blueTest for Hydrogen:The pop test. Lit splint → popElectroplating: At the negative electrode – Copper ions gain electrons (reduction) to form Copper metal. Cu   + 2e  → Cu At the positive electrode – Copper strip loses electrons (oxidisation) to form Copper ions. The positive electrode dissolves Cu – 2e  → Cu  - where its being plated.  The electrolyte contains ions of the plating metal.  Electroplating is useful because we can plate items to make them look nicer and its cheaper than using pure metal. 

Copper plating

Copper plating:Negative Electrode – Copper goes to the Negative electrode because they are positive ions. They gain 2 electrons and are reduced. This makes a layer of Copper on the nail.                    Cu   + 2e  → CuPositive Electrode – Sulphate stays in solution. (The solution is losing copper ions and it wants them back. This is because the positive electrode is being dissolved). The copper atoms at the copper electrode lose electrons, they are oxidised. This forms copper ions which go back into the solution. Cu – 2e  → Cu  The concentration of the solution stays the same because the copper is lost at the same time it is gained. It is losing/ gaining electrons at a steady rate.