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 E^o - 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