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ELECTROLYSIS OF BRINE Noadswood Science, 2012. Electrolysis Of Brine Tuesday, May 05, 2015  To understand the electrolysis of brine (salty water)

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Presentation on theme: "ELECTROLYSIS OF BRINE Noadswood Science, 2012. Electrolysis Of Brine Tuesday, May 05, 2015  To understand the electrolysis of brine (salty water)"— Presentation transcript:

1 ELECTROLYSIS OF BRINE Noadswood Science, 2012

2 Electrolysis Of Brine Tuesday, May 05, 2015  To understand the electrolysis of brine (salty water)

3 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

4 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…

5 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

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

7 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

8 Positive Electrode  At the positive electrode, negatively charged ions lose electrons  This is oxidation – the ions have been oxidised -ve Ion In SolutionElement Given Off At +ve Electrode Chloride, Cl - Chlorine, Cl 2 Bromide, Br - Bromine, Br 2 Iodide, I - Iodine, I 2 Sulfate, SO 4 -2 Oxygen, O 2

9 Ionic Compounds & Electrolysis  Common ionic compounds and the elements released when their solutions are electrolysed: - Ionic Substance In SolutionElement At –ve ElectrodeElement At +ve Electrode Copper chloride, CuCl 2 CopperChlorine Copper sulfate, CuSO 4 CopperOxygen Sodium chloride, NaClHydrogenChlorine Hydrochloric acid, HClHydrogenChlorine Sulfuric acid, H 2 SO 4 HydrogenOxygen

10 Brine  Brine is concentrated sodium chloride solution – if an electric current is passed through it, hydrogen gas forms at the negative electrode and chlorine gas forms at the positive electrode (a solution of sodium hydroxide forms)  Sodium metal is not deposited at the negative electrode as it is too reactive for this to happen – hydrogen is given off instead…

11 Experiment  Complete the brine electrolysis experiment – write the equation for the electrolysis of brine at the cathode (-ve) and anode (+ve)

12 Brine  Sodium chloride dissolved in water is called brine – electrolysis of brine gives hydrogen at the cathode and chlorine at the anode (sodium hydroxide remains dissolved in the solution)  The reactions at each electrode are ½ equations – the ½ equations are written so that the same number of electrons occur in each equation 2H + + 2e - → H 2 (hydrogen gas at the –ve cathode) 2Cl - - 2e - → Cl 2 (chlorine gas at the +ve anode)

13 Brine  Hydrogen ions gain electrons (reduction) to form hydrogen atoms – the hydrogen atoms combine to form molecules of hydrogen gas  Chloride ions lose electrons (oxidation) to form chlorine atoms – the chlorine atoms combine to form molecules of chlorine gas 2NaCl + 2H 2 O → 2Na+ + 2OH - + Cl 2 + H 2

14 Products  These three products - hydrogen, chlorine and sodium hydroxide all have important uses in the chemical industry…  Hydrogen: making ammonia; making margarine etc…  Chlorine: killing bacteria in drinking water; killing bacteria in swimming pools; making bleach; making disinfectants; making hydrochloric acid; making PVC; making CFC's etc…  Sodium hydroxide: making soap; making paper; making ceramics etc…


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