last chem 12 test. lfg

oxidation

species loses one or more electrons

reduction

species gains one or more electrons

reducing agent

the species which oxidizes and causes the other species to reduce

oxidizing agent

species which is reduced and causes the other species to oxidize

which redox reactions will react spontaneously

stronger oxidizing agent with a stronger reducing agent (high left, low right)

how do you balance a HALF redox reaction

balance: major species, O with H2O, H with H+, charge with e-

how do you balance redox reactions

balance half reactions, multiply the equations so that the electrons cancel, cancel other species that appear on opposite sides

how to balance redox reactions in BASIC solutions

follow same steps as before but add H2O → OH- + H+ at the end to cancel out the H+

oxidation number

a charge of an atom within a substance

how to find the oxidation number of an element within a substance

write down the known oxidation numbers, let the element in bold be x, solve for x and let the sum equal the total charge

where do electrons vs ions flow through?

electrons flow through the wire, ions flow through the salt bridge

in an electrochemical cell, oxidation occurs at the

anode

in an electrochemical cell, reduction occurs at the

cathode

in a salt bridge, anions flow towards…

the anode

in a salt bridge, cations flow towards..

the cathode

electrons will go in what direction in a wire

from anode to cathode

in an electrochemical cell, the ion on the bottom of the beaker will go AWAY from the

anode

since oxidation occurs at the anode and reduction occurs at the cathode, what does it mean for their masses?

the element on the anode will decrease in mass while the element on the cathode will increase in mass

if cell potential is positive..

the reaction is spontaneous

if cell potential is negative..

the reaction is not spontaneous

what does E^o _cell equal

E_red - E_ox

corrosion

oxidation of any metal

rusting

describes the corrosion of iron

when water is placed onto a piece of iron, which areas are oxygen rich vs poor?

the surface of water is oxygen rich while the center of the droplet is oxygen poor

what happens at the surface of a water droplet on a piece of iron

oxygen in the atmosphere and the water are going to interact with two electrons which become two hydroxide ions: 1/2O₂ + H₂O + 2e^- → 2OH^-

what happens to the iron at the center of the droplet

the iron turns into Fe²⁺ + 2e^- which causes pitting, that Fe²⁺ migrates to the edges of the water and a precipitate of Fe(OH)₂ forms

what happens with the Fe(OH)₂ formed when the water droplet dries

will further oxidize and produce Fe₂O₃ with a variety amounts of water

what is pitting/what does it do to iron

forms dimples in the metal over time

name four ways to prevent corrosion

coatings, attaching metal to negative terminal of the battery, anodizing, change the chemical surroundings

how does coatings prevent corrosion

paint, grease, plastic prevents O₂ and moisture from contacting the surface of the metal

how does attaching a metal to the negative terminal of a battery prevent corrosion

electrons are pushed onto the surface and prevents the metal from losing electrons

anodizing/cathodic protection/sacrificial protection - how does it prevent corrosion

attach a more reactive metal which corrodes instead of the metal you want to protect

change the chemical surroundings - how does it prevent corrosion

remove O₂ or remove H⁺ by adding NaOH aka increase pH

what type of redox reaction is required for electrolytic cells

not spontaneous, endothermic, and requires electricity to make the reaction occur

molten

melted (l)

aqueous

dissolved in water

anode

electrode where oxidation occurs and attracts anions

cathode

electrode where reduction occurs and attracts cations

inert

does not react, usually Pt or graphite

what is the simplest form of electrolytic cells

molten salts

how do you find the minimum voltage for a cell to run

same procedure as solving for cell potential

what is the overpotential effect and how does it effect others

some substances react before expected because of the activation energy of water

for complex electrolysis of aqueous salt with inert electrodes, how many reductions occur at the cathode/ how many oxidations occur at the anode

two possible reductions/oxidations at each

what water equation will occur at the cathode of a complex electrolytic cell of an aqueous salt with inert electrodes

2H₂O + 2e^- → H₂ + 2OH^-

what water equation will occur at the anode of a complex electrolytic cell of an aqueous salt with inert electrodes (oxidation)

H₂O → 1/2O₂ + 2H⁺+ 2e^-

how can you determine the two reactions that will occur in a complex electrolytic cell of an aqueous salt with inert electrodes

the reaction that is the closest redox pair

what does the arrow of the overpotential effect tell us about the water equation

the head of the arrow shows where the equation actually is on the chart

in a complex electrolytic cell involving an aqueous salt with reactive electrodes using electroplating, which item is to be plated and how

the cathode which will end up being coated with Cu since it will attract the Cu²⁺ in solution and the equation Cu²⁺ + 2e^- → Cu will occur

in a complex electrolytic cell involving an aqueous salt with reactive electrodes using electroplating, what is the anode made of?

copper (Cu), where it will replace Cu²⁺ ions and give off Cu²⁺ to the cathode from Cu→Cu²⁺ + 2e^-

what is bauxite

impure mineral of Al (Al₂O₃)

what does cryolite do in the production of aluminum

it is added to the pure aluminum to reduce its melting point

what is the chemical compound of cryolite

Na₃AlF₆

overview: how do you produce aluminum (no water involved)

purify and dry Al₂O₃, add it to cryolite and melt it, ions are released, reactions at the electrodes occur, aluminum will flow down the edges of the container and get collected as molten aluminum

in the production of aluminum, what is your cathode and what is your anode

the cathode is the container which is iron and the anode is carbon

what happens at the iron cathode when producing aluminum (Al³⁺ + 3e^- → Al)

Al³⁺ and Na⁺ are attracted to the cathode where Na will remain as an ion since it is more reactive, meanwhile Al will be reduced down and turned into the metal

what happens at the carbon anode when producing aluminum

F^- and O^2- are attracted to the anode, since F is more reactive, the oxygen ion will react with the carbon anode

how do you find the balanced redox equation for aluminum production

combine the two half-reactions at the cathode (Al³⁺+ 3e^- → Al) and the anode (C+2O^2- → CO₂ + 4e^-)

what are 2 different applications of electrochemical cells

batteries, cathodic protection of metals

what are three applications of electrolytic cells

electroplating, electrofining, and aluminum production

how would you produce Na from NaCl (l)?

the same process of molten salts occur except the atmosphere would be inert and Cl₂ would have to be removed to prevent it reacting with Na. then Na will float since it has low density

oxidation number of hydrogen in a compound

+1

oxidation number of alkali metal ions (group 1)

+1

oxidation number of alkaline earth metals (2)

+2

oxidation number of oxygen

-2 unless it is in a peroxide (H₂O₂) where it is -1

when several different half reactions occur, which will occur preferentially?

the half reaction with the highest reduction potential and the half reaction with the lowest reduction potential will occur preferentially