electrochemistry ch. 17

ElectrochemistryCh. 17

Moving Electrons• 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

• 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 CAThodeOxidation at the Anode

????

Electrolytic Cell• If the following compound was separated using

electrolysis: 2Al2O3 4Al(s) + 3O2(g)

1) What is oxidized/reduced?

2) What are the cations/anions?

3) What elements will move to the cathode/anode?

Al; +30, reduced O; -20, oxidized

Al+3Cation O-2Anion

Al+3Cathode O-2Anode

Using Electrolysis• Removing elements from compounds:

2NaCl(aq)+2H2O(l)Cl2(g)+H2(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

• 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 H2O inside it?

A Hydrate2) Al2O3 is heated to about 1000oC3) Molten Al2O3 goes through electrolysis

Refining Aluminum • In a electrolytic cell with

Carbon anodes, oxygen is drawing towards the carbon to produce CO2

• Al ions settle on the bottom of the container making pure liquid aluminum

2Al2O3(s)+3C(s)4Al(l)+3CO2(g)

• What is oxidized/reduced?Al; +30, reduced C; 0+4; oxidized

Electroplating• Reactive metals need a

protective coating to prevent rusting or tarnishing

• Zinc makes a great coat for steel

• Metal plating using gold, silver, and copper is also common

• Object to be plated cathode• Metal coating anode

Electrolytic Cleaning• Cleaning objects by

pulling ions of chemical build up

• Antiques coated in salts• Old object cathode• Stainless steel anode• 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?

• MgSO4 and CuSO4 containers are connected by a salt bridge– Keeps solutions separate but allows ion movement– Mg2+ ions build up at anode; Cu2+ removed at cathode– Salt ions neutralize a build up of charges as the Mg2+/Cu2+

change places

Mg: oxidized; becomes the anodeCu: reduced; becomes the cathode

Types of Batteries• Carbon-Zinc Dry Cell– Carbon center

(cathode); MnO2 coating– Zinc cover (anode)– Electrolyte gel (NH4Cl-

ZnCl2)

• Zinc is oxidized; Zn Zn2++2e-

• Manganese is reduced; 2MnO2+H2O+2e- Mn2O3+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)Pb2++2e-

Pb+4+2e-Pb2+

• Pb2+ combines with SO42- ions

• Both anode and cathode collect PbSO4

• 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 H2O 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