Chem Unit 11: Electrochemistry

Electron Transfer Reactions

  • electron trander reations are called redox

  • results in electricity (spontatnous) or can be imposed by putting in an electron current (non-spontatnous)

  • “electrochemistry”

History

  • originally called oxidation because a compound would bind with oxygen to make an oxide

  • reductions If it lost oxygen because it lost volume

Terminolgy for Redox Reactions

  • Oxidation - loss the electrons, increase in oxidation number, increase in oxygen

  • Reduction - gain in electrons, lower oxidation number, decrease in oxygen, increase in hydrogen

  • Oxidizing Agent - is the electron acceptor, and is reduced, “helps oxidize”

  • Reducing Agent - electron doner, is oxidized, helps reduce

In a reaction, oxidation and reduction agent both have to be in the same equation

Oxidation Numbers

  • monoatomic ions - their charge

  • Hydrogen - +1 (when acts like a metal) or -1 (when acting like nonmetal)

  • Oxygen - always -2 except in peroxides where it is -1

  • Uncombined element or free element - is 0

  • Neutral Compound - the sum of the oxidation number is 0

  • Polyatomics - the sum of oxidation number is the charge of the poly atomics

  • Group 1 metals are +1, and group 2 are +2, flourine is always -1

Electrochemistry

  • electrochemical reactions are spontaneous (chemcial → electricity) or nonspontatnous (electric → chemical)

  • half reactions

  • voltaic/ galvanic cell

  • Direct redox reaction - oxidation and reduction in direct contact “same container”

  • Indriect Redox Reaction - occurs in different containers and the elctrons are transferred with a wire

  • reactions occur at the same time at different electrodes

  • reduction and oxidation occur in the cathode

Balancing Redox

  • separate into half reactions

  • balance the atoms

  • add h2o and H+ and e- to balance

  • cancel out the electrons

  • add together and cancel out

  • if basic add OH to the H+ on both studies

  • to check, check the charges and atoms

Galvanic/ Voltaic Cells

  • Anode - is negative and is the source of the electrons (electrode), the electrode will gain mass

  • Cathode. - is positive and is the sink for electrons (electrode), the electrode will turn into the solution

  • Electrons move through a wire

  • salt bridge is to balance the charges and maintain the efficiency

  • Product Favroed reaction

Batteries

  • Dry Cell Battery:

    • The anode is usually Zn (reduction agent, oxidized, electron donator). Zn Case

    • The Cathode is usually NH4+

    • conductor is Graphite

    • Porous Seperator

    • Paste

  • Alkaline Battery

    • under basic conditions

    • anode is Zn

    • cathode is MnO2

  • Mercury Battery

    • under basic conditions

    • anode is Zn

    • cathode is HgO

  • Lead Storage Battery

    • acidic

    • large batteries in cars

    • Anode is Lead Grids

    • Cathode is Spongy Led

  • Ni-Cad Batteruy

    • Rechargable and basic

    • anode is Cd

    • Cathode is NiO

  • Li-Ion Battery

    • anode is LiC6

    • Cathode is CoO2

  • H2 Fuel

    • H2 is oxidized

    • O2 is reduced

Calculating Voltage

  • Standard Cell Potential Eo - is the quantitative measure of the tendency of reactnats to proceed to products when all are at their standard states

Calculating using the Standard Reduction Potentials

  • if we know the E of each half reaction we could get the net E

  • E = E(of the reduced more positive) - (oxididized E)

  • more positive value is what is being reduced’

  • From Table vs As written

    • if its as written then the reaction has to be organized as so and the equation may result in a negative voltage which means its non spontaneous

Electrlysis

  • the reatants are favored

  • electric current used to make a chemical change

  • the E is negative

  • electrochemical energy is used to bring a chemical change

  • nonsponatnous reactions

  • oxidation is anode, reduction is at cathode but the symbols are reversed

Examples:

  • water → H and O

  • gold plating

The Busy Electron

  • oxygen is very reactive

  • electron transfer → redox

Effects:

  • corrosion

  • Metal Atoms give their electorns to oxygen “electronegative:”

  • Iron → Iron Oxide (Rust)

  • Copper → Copper Oxide (green protective layer) Blocks out moisture and oxygen

  • Aluminum → aluminum oxide

  • Paint to prevent oxidation

External conditions can make increase oxidation rate

  • raising temperature

  • presence of calcium

  • in salt water “can conduct electrons”

Uses:

  • Zinc metal in copper solution → copper plating

  • batteries:

    • have bridge or connected by a porous barrier

  • Lithum cell -

    • was light and very reactive “lots of volts”

    • good for pace makers

    • litherum anode - magenese cathode

    • has a membrane to allow ions through “salt brige”

  • Lead Battery

    • used for cars

    • Several Cells

    • Led and Led Dioxide in sulfuvic acid

Electrloylsis

  • electricity used to do nonsponatnous reactions

  • to plate metals

  • can separate water into hydrogen gas and oxygen

  • used for solar power

  • removing rust

The Metallic World: Electrochem and Coordination Compounds (Video)

  • Electrochemistry: the transfer of electrons and can power batteries = needs metals

    • redox: one gains and another loses electrons

  • Redox Reactions in the Body

    • require trace metals

    • B12 B9 - essential to prevent heart disease and birth defects

  • Oxidation loses electrons, reduction gains electrons

  • Transition Metals - can have many different charges and this changes the oxidation numbers

Redox in a single solution

  • A zinc metal put into a copper ion solution

  • since a copper ion is higher up on the recution table, the zinc will give up its electrons and makes the copper a solid

  • zinc will disolve because it is oxidized (recution agent)

Batteries:

  • Redox Reactions are spontaneous

  • Movement of electrons make a voltage

  • betteires use 2 different hald reactions

  • the wire is where the electorns transfer and this energy is harvested

  • electrodes are connected

  • salt bridge: to balance the charges that are created NaCl

  • volt meter (shows the pressure)

Redox in Body:

  • transforming food into energy

  • Vitamins have trace metals and are molecules found in food

  • B12 methionine - is found in meat and fish and B9 folate- prevents heart disease and promote cell division (mitosis)

    • has cobalt and has oxidation +1, 2, 3

    • The number of electrons gained or lost is determined by the oxidation number

  • anaerobic chamber - used to study

  • oxidation numbers change how vitamins react

  • co+1 - allows folic acid usage - cell replication

  • co+3 - helps make methionine amino acid

  • folic acid is B9 - and reacts with B12 cobalt

  • Vitamin B2 makes the cobalt from +2 to +1 which is more useful

Spontanous - will just happen

Non spontaneous - needs energy to happen - “electrolytic”

-bleaching hair - redox - hydrogen peroxide and melanin, melanin is oxidized