Electrolysis Noadswood Science, 2012

Electrolysis To understand electrolysis and products it makes Wednesday, April 26, 2017 Electrolysis To understand electrolysis and products it makes

Ionic Ionic substances form when a metal reacts with a non-metal – they contain charged particles called ions For example, sodium chloride forms when sodium reacts with chlorine – it contains positively charged sodium ions and negatively charged chloride ions Ionic substances can be broken down by electricity

Electrolysis Electrolysis is the process by which ionic substances are decomposed (broken down) into simpler substances when an electric current is passed through them For electrolysis to work, the ions must be free to move – ions are free to move when an ionic substance is dissolved in water or molten For example, if electricity is passed through copper chloride solution, the copper chloride is broken down to form copper metal and chlorine gas…

Electrolysis Positively charged ions move to the negative electrode during electrolysis – they receive electrons and are reduced Negatively charged ions move to the positive electrode during electrolysis – they lose electrons and are oxidised OILRIG – oxidation is loss, reduction is gain

Electrolysis

Electrolysis Products Ionic substances in solution break down into elements during electrolysis – different elements are released depending on the particular ionic substance…

Negative Electrode At the negative electrode, positively charged ions gain electrons – this is reduction (ions have been reduced) Metal ions and hydrogen ions are positively charged – whether you get the metal or hydrogen during electrolysis depends on the position of the metal in the reactivity series: - The metal will be produced if it is less reactive than hydrogen Hydrogen will be produced if the metal is more reactive than hydrogen E.g. the electrolysis of copper chloride solution produces copper at the negative electrode, but the electrolysis of sodium chloride solution produces hydrogen

Element Given Off At +ve Electrode Positive Electrode At the positive electrode, negatively charged ions lose electrons This is oxidation – the ions have been oxidised -ve Ion In Solution Element Given Off At +ve Electrode Chloride, Cl- Chlorine, Cl2 Bromide, Br- Bromine, Br2 Iodide, I- Iodine, I2 Sulfate, SO4-2 Oxygen, O2

Anode & Cathode

Copper Copper is a good conductor of electricity, and is used extensively to make electrical wiring and components The extraction of copper from copper ore is done by reduction with carbon, however, the copper produced is not pure enough for use as a conductor, so it is purified using electrolysis

Copper Electrolysis In this process, the positive electrode (anode) is made of the impure copper which is to be purified. The negative electrode (cathode) is a bar of pure copper. – the two electrodes are placed in a solution of copper(II) sulfate… Copper ions leave the anode and are attracted to the cathode, where they are deposited as copper atoms – the pure copper cathode increases greatly in size, while the anode dwindles away (he impurities left behind at the anode form a sludge beneath it)

Copper Electrolysis Copper purification via electrolysis…

Experiment Complete the copper electrolysis experiment…

Aluminium In the electrolysis of aluminium from its bauxite ore, cryolite it used to lower the temperature (cryolite is a less common ore of aluminium) The electrodes are made of carbon

Half Equations A half-equation shows you what happens at one of the electrodes during electrolysis – electrons are shown as e- A half-equation is balanced by adding, or taking away, a number of electrons equal to the total number of charges on the ions in the equation… At the negative electrode – positive ions gain electrons at the negative electrode, so are reduced: - Cu2+ + 2e- → Cu At the positive electrode – negative ions or neutral atoms lose electrons at the positive electrode and are oxidised: - Cu → Cu2++ 2e-

Half Equations A half-equation shows you what happens at one of the electrodes during electrolysis – electrons are shown as e- A half-equation is balanced by adding, or taking away, a number of electrons equal to the total number of charges on the ions in the equation… At the negative electrode – positive ions gain electrons at the negative electrode, so are reduced: - Al3+ + 3e- → Al At the positive electrode – negative ions or neutral atoms lose electrons at the positive electrode and are oxidised: - 2O2- → O2 + 4e-

Half Equations A half-equation shows you what happens at one of the electrodes during electrolysis – electrons are shown as e- A half-equation is balanced by adding, or taking away, a number of electrons equal to the total number of charges on the ions in the equation… At the negative electrode – positive ions gain electrons at the negative electrode, so are reduced: - 2H+ + 2e- → H2 At the positive electrode – negative ions or neutral atoms lose electrons at the positive electrode and are oxidised: - 2Cl- → Cl2 + 2e-