Electrochemistry Ch. 17

Moving Electrons What kind of chemical reaction relates to the concept of electricity? What kind of chemical reaction relates to the concept of electricity? Redox Reactions: electrons are moving from atom to another; moving electrons produce electricity Battery: controlled chemical reaction to produce an electrical current Battery: controlled chemical reaction to produce an electrical current Electrolysis: using electricity to causes a chemical reaction Electrolysis: using electricity to causes a chemical reaction

Electrolysis Electrolytic cell- device, when attached to a power source (battery) induces a chemical reaction Two Electrodes: Cathode- releases electrons, takes in Cations (negatively charged) Anode- takes electrons, takes in Anions (positively charged) RED CAT??? REDuction at the CAThode Oxidation at the Anode ????

Electrolytic Cell If the following compound was separated using electrolysis:2Al 2 O 3  4Al (s) + 3O 2(g) If the following compound was separated using electrolysis:2Al 2 O 3  4Al (s) + 3O 2(g) 1)What is oxidized/reduced? 2)What are the cations/anions? 3)What elements will move to the cathode/anode? Al; +3  0, reduced O; -2  0, oxidized Al +3  CationO -2  Anion Al +3  CathodeO -2  Anode

Using Electrolysis Removing elements from compounds: 2NaCl (aq) +2H 2 O (l)  Cl 2(g) +H 2(g) +2NaOH (aq) Refining Ores- remove pure metal from compounds found in the Earth Electroplating- cheap and effective why to coat and protect reactive metals Electrolytic Cleaning- restoring aged materials

Refining Ores Before refining aluminum was possible, pure aluminum was more rare than gold or sliver Before refining aluminum was possible, pure aluminum was more rare than gold or sliver Today it is one of the most widely used metals Today it is one of the most widely used metals Bauxite Ore  Pure Aluminum 1)Heat the Bauxite Ore to remove water and impurities. What is a compound with H 2 O inside it? A Hydrate 2) Al 2 O 3 is heated to about 1000 o C 3) Molten Al 2 O 3 goes through electrolysis

Refining Aluminum In a electrolytic cell with Carbon anodes, oxygen is drawing towards the carbon to produce CO 2 In a electrolytic cell with Carbon anodes, oxygen is drawing towards the carbon to produce CO 2 Al ions settle on the bottom of the container making pure liquid aluminum Al ions settle on the bottom of the container making pure liquid aluminum 2Al 2 O 3(s) +3C (s)  4Al (l) +3CO 2(g) What is oxidized/reduced? What is oxidized/reduced? Al; +3  0, reduced C; 0  +4; oxidized

Electroplating Reactive metals need a protective coating to prevent rusting or tarnishing Reactive metals need a protective coating to prevent rusting or tarnishing Zinc makes a great coat for steel Zinc makes a great coat for steel Metal plating using gold, silver, and copper is also common Metal plating using gold, silver, and copper is also common Object to be plated  cathode Object to be plated  cathode Metal coating  anode Metal coating  anode

Electrolytic Cleaning Cleaning objects by pulling ions of chemical build up Cleaning objects by pulling ions of chemical build up Antiques coated in salts Antiques coated in salts Old object  cathode Old object  cathode Stainless steel  anode Stainless steel  anode Chlorine and other salt compounds can be removed Chlorine and other salt compounds can be removed

Electrochemical Cells A spontaneous redox reaction that can be used to produce an electrical current Required: – A metal cathode; site of reduction – A metal anode; site of oxidation – An electrolyte solution; allow transfer of electrons The type of metal used determines if it is a cathode or an anode – Metal more easily reduced is cathode – Metal more easily oxidized is anode

Potential Difference The type of metal and the amount used determines the strength of the electrical current Potential difference- difference between how easily the anode is oxidized and the cathode is reduced – Voltage (Alessandro Volta) Which produces a larger voltage; a current between Lithium/Zinc or Sodium/Magnesium? Why is it better to make jewelry out of Gold, Silver, Copper, and Platinum? Lithum/Zinc Not very reactive; wont corrode

Galvanic Cells Battery (voltaic cell)- controlled spontaneous redox reaction to produce a current Mg/Cu Galvanic Cell: 1)What is oxidized/reduced? What is the cathode/anode? MgSO 4 and CuSO 4 containers are connected by a salt bridge – Keeps solutions separate but allows ion movement – Mg 2+ ions build up at anode; Cu 2+ removed at cathode – Salt ions neutralize a build up of charges as the Mg 2+ /Cu 2+ change places Mg: oxidized; becomes the anode Cu: reduced; becomes the cathode

Types of Batteries Carbon-Zinc Dry Cell – Carbon center (cathode); MnO 2 coating – Zinc cover (anode) – Electrolyte gel (NH 4 Cl- ZnCl 2 ) Zinc is oxidized; Zn  Zn 2+ +2e - Manganese is reduced; 2MnO 2 +H 2 O+2e -  Mn 2 O 3 +2OH -

Types of Batteries Lead Storage Battery – Lead (IV) Oxide electrode – Lead electrode – Sulfuric acid electrolyte Lead (IV) is reduced and Lead is oxidized Pb (metal)  Pb 2+ +2e - Pb +4 +2e -  Pb 2+ Pb 2+ combines with SO 4 2- ions Both anode and cathode collect PbSO 4 Reaction reversible

Alternative Batteries NiMH battery (Nickel + Metal Hydride) – Rechargeable – Use electrolysis to reverse the redox reaction – Lose 1% of their charge a day when even not used Lithium battery – Holds a more charge – Li is easiest to oxidize (produces a large potential difference) – Li explodes in water

Alternative Batteries Hydrogen-Oxygen Fuel Cell – Electrodes are inert metals – Produces H 2 O as by-product – Could be possible alternative to gasoline cars – Hydrogen and Oxygen are very abundant elements on earth Super Battery? – In 2009 a Lithium super battery was produced using nano- engineering – Releases energy 100 times faster – Could recharge an electric car faster than it takes to pump gas into a gasoline car