GChem: Electrochemistry and Nuclear Chem

Question 1

How do you get reduction and oxidation?

What is a standard reduction potential?

What is the oxidation state of W in W(CO)6? Zn in Zn(NO3)Cl?

Answer 1

Reduction -> more e-
Gaining bonds to less EN atoms (H)
Lose bonds more EN atoms (O)

F>O>(N≈Cl≈Br)>(I≈S≈C)>H (a lil)

Oxidation -> gain e-
Losing bonds to less EN atoms (H)
Gaining bonds to more EN atoms (O)

Standard reduction potential is the likelihood that a species will be reduced

W oxidation state is 0
Zn oxidation state is +2

Question 2

*What does a double bond to oxygen mean in terms of oxidation states

When question asks which was more oxidized/reduced, what do you do?

Answer 2

A double bond to oxygen is 2 bonds to oxygen then thinking about oxidation states

Calculate the oxidation state by using the oxidation rules and look at the oxidation state of central atom/atom you want to focus on by comparing its before and after value

Question 3

What is Eº/standard reduction potential? Is a high reduction potential pos or neg?
What sign means spontaneous/non-spontaneous?

Oxidation potentials are for the ______ of reduction half reactions. Oxidation potentials are the _____ of the reduction potentials

Answer 3

Tell you how much reactant want e- (neg Eº means don’t want, the more pos it is the more reactant wants e-)
Highest reduction potential (highest positive value)
A practice question said “value of the standard voltage is negative, and therefore non-spontaneous” and “Zn2+ has an Eº < 0, so its reduction is not spontaneous, making it a poor oxidizing agent”

Oxidation potentials are for the “products” of reduction half reactions. Oxidation potentials are the negative of the reduction potentials

Question 4

What is a galvanic cell/voltaic cell?

What basic elements does it consist of? What do the electrolytes do?

Answer 4

A galvanic cell is a device in which we can determine the electric current
Flow of e- constitutes an electric current that can do work, we can use a spontaneous redox reaction to generate an electric current
anode connected to cathode with ammeter attached in between to measure electric current
The anode and cathode are each in a half-cell with electrolytes inside
Since the e- move in one direction (anode to cathode), the electrolytes flow in opposite direction to counteract that movement so the positive electrolytes move to cathode and neg electrolytes to anode
The electrons going to cathode will plate that metal and at the same time, the metal from the neg side (anion) is going to dissolve (pitting)
A salt bridge also connects. the two half-cells

Question 5

What happens in galvanic cell? (see page 266)
The e- travel from where to where?
The anode is always the site of oxidation/reduction, and the cathode is always the site of oxidation/reduction
Popular neumonic to remember?

Answer 5

The electrons travel from anode to cathode
The anode is always the site of oxidation, and the cathode is always the site of reduction

An ox, red cat

Question 6

We often use a cell diagram to illustrate what’s in the galvanic cell, what does it look like/mean?

Answer 6

Anode | Anodic solution (concentration) | | Cathodic solution | Cathode

If the concentrations are not specified in the cell diagram, you would assume they are 1M

Question 7

To determine whether the redox of a cell is spontaneous and can produce an electric current, we need to figure out the cell ___.
Each half rxn has a potential (E) and we usually consider standard conditions: 25ºC, 1M, 1 atm, with substances in their standard states
By adding the half-reaction potential for a given pair of electrodes, we get the cell’s overall _____.

Answer 7

To determine whether the redox of a cell is spontaneous and can produce an electric current, we need to figure out the cell voltage.

By adding the half-reaction potential for a given pair of electrodes, we get the cell’s overall voltage

Since each cell has a reduction half-reaction and an oxidation half-reaction, we get the potential of the oxidation by simply reversing the sign of the corresponding reduction potential

Question 8

• The free-energy change, ΔGº, for a redox reaction in which cell voltage is Eº is given by the equation:
• When will the redox reaction in a cell be spontaneous>

Answer 8

ΔGº = - nFEº
n is moles
F is faraday’s constant (usually given to you) 95,485(charge of 1 mole of e-) = 96,500 Coulombs
The redox reaction in a cell be spontaneous if the cell voltage is positive
Ecell>0 -> spontaneous
Ecell<0 -> nonspontaneous

Question 9

If the cell voltage is positive, then the reaction is ______

If the cell voltage is negative, then the reaction is _____

Answer 9

If the cell voltage is positive, then the reaction is spontaneous
If the cell voltage is negative, then the reaction is non-spontaneous

Question 10

When get a full reaction like: Au + Cu2+ -> Au3+ + Cu
can break it down into half reactions:
Au -> Au3+ + 3e- Eº= -1.50V
Cu2+ + 2e- -> Cu Eº = +0.34V
But now what do you have to do to get cell voltage?

Answer 10

You have to make sure it is electron balanced, so multiply the whole first rxn by 2 and the second by 3 BUT DO NOT MULTIPLY THE Eº BC THAT IS AN INTRINSIC PROPERTY OF THE HALF RXN AND DOES NOT CHANGE WITH MOLES

Question 11

*What is an oxidizing agent? Reducing agent?

The more neg the reduction potential, the stronger/weaker the reactant is as an oxidizing agent, and the stronger/weaker the product is as a reducing agent
The more positive the reduction potential, the stronger/weaker the reactant is as an oxidizing agent, and the stronger/weaker the product is as a reducing agent

Answer 11

An oxidizing agent is a substance that causes oxidation by accepting electrons; therefore, it gets reduced. A reducing agent is a substance that causes reduction by losing electrons; therefore it gets oxidized.

The more neg the reduction potential, the weaker the reactant is as an oxidizing agent, and the stronger the product is as a reducing agent
The more positive the reduction potential, the stronger the reactant is as an oxidizing agent, and the weaker the product is as a reducing agent

Question 12

How do you get the value for n in ΔGº = - nFEº?

Answer 12

When you balance the amount of e-, use the new coefficient of the e-
example on page 271, can practice if want

Question 13

The table for Eºis for standard conditions (1 atm, 1M, 25ºC) but conditions are not always standard so to describe the voltage of an electrochemical reaction we have to use the Nernst equation:
It describes how deviations in temp and concentration of reactants can alter the voltage of a reaction under nonstandard conditions
The concentrations of products and reactants will change until equilibrium is reached when Q =____ and E =____

Answer 13

E = Eº - (RT/nF) ln(Q)

The concentrations of products and reactants will change until:
Q = Keq and E = 0

Question 14

(maybe extra?) Concentration cell -> what is it, when does it stop? How do e- flow?

Answer 14

It is a galvanic cell that has identical electrodes but has half cells with difference ion concentrations so there will be potential difference (thus current) between them
Eº is not 0 bc cell is not standard bc both half cells not 1M
e- flow to the half-cell with higher concentration of pos ions so the lower conc pos ion electrode will serve as anion and e- flow to higher conc electrode which serves as the cathode
When concentrations of the solutions become equal, the reaction will stop

Question 15

Redox titrations:
involve redox indicator much like an indicator in acid/base chem, a redox indicator uses a change in color to determine the endpoint
What is this change in color due to?
What is cerimetry?
Ce4+ often used for this (strong oxidant), C4+ turns yellow but colorless when reacted/reduced (oxidizes secondary alcohol to ketones)

Answer 15

Cerimetry is a common type of redox reaction
Change in color due to change in oxidation state
Solution will turn yellow immediately after all oxidizable hydroxyls have been consumed
Knowledge of the concentration of the Ce4+ titrant allows for the determination of initial alcohol concentration

Question 16

When will the solution turn yellow? Knowledge of the concentration of the Ce4+ titrant allows for the determination of: ______
Similar to the acid-base titration curve, plot looks the same with an equivalence and half-equivalence point
What does the equivalence point mean here? Half-equivalence point? When is
E = Eº - (RT/nF) ln(Q) applicable? What does Q mean? What does Q equal at half-equivalence point?

What happens at twice the equivalence point?

Answer 16

Equivalence point here means the solution turned yellow and indicates the completion of the redox reaction and the total consumption of the reductant as described by the system’s balanced redox equation.
Ce4+ + e- -> Ce3+ (titrant)
Means equal amounts of Ce4+ (yellow) and Ce3+ (colorless)
The half equivalence point significance can be seen in the Nernst equation:
E = Eº - (RT/nF) ln(Q)
Q refers to ratio of oxidized and non-oxidized reactant. At the half equivalence point these two quantities are equal and Q=1. Since ln(1) = 0, at the half equivalence point the value of E is equal to the value of Eº for the redox couple
being titrated
At half equivalence point, the measured E will be equal to Ecell of species being titrated, so
E = Eºred(which is sample)
At twice the equivalence point, E measured is equal to E cell of species that is the titrant
E = Eºred(which is titrant)

Question 17

What is iodometry?

Answer 17

Iodometry = Redox titration where the consumption of iodine indicates the end point
When see blue we reached endpoint (when I3- is produced which is the third rxn) and can tell how much we started with (concentration)

Question 18

What is the main difference between galvanic cell and electrolytic cells?
What can happen to the cathode?

Answer 18

Electrolytic cell uses an external voltage source (such as a battery) to create an electric current that forces a non spontaneous redox reaction to occur (negative E) = electrolysis
Electroplating can occur in which the cathode is plated with metal of the other electrolytic cell

Question 19

What is the same and different b/w galvanic and electrolytic cells (in terms of ΔEº, ΔGº, pos/neg, where e- move, what is site of oxidation/reduction?

Also side note, the current (conventional direction) and actual movement of e- are opposite, but here we focus on e- movement to know where plating/pitting takes place

Answer 19

Both -> 
anode = site of oxidation 
cathode = site of reduction 
e- move from anode to cathode 
plating at cathode, pitting at anode ALWAYS 

Differences: 
Galvanic cell/voltaic 
Discharging battery, 
NO external power source
-> spontaneous redox reaction to create current, ΔGº < 0 
-> ΔEº > 0 and I think decreases 
-> anode= neg, cathode = pos

Electrolytic cell
Recharging battery, external power source
-> non spontaneous redox reaction to create current, ΔGº > 0
-> ΔEº < 0 and Ecell increases
-> anode =pos, cathode = neg

If confused -> rewatch the review video, very helpful

Question 20

Could help but idk:

Most common example of electrolytic cell

Answer 20

sodium metal and chlorine gas from molten NaCl

There is reduction at cathode
Na+ + e- -> Na

There is oxidation at anode
2 Cl- -> Cl2 + 2e-

Question 21

Common rechargeable batteries
Car batteries, a.k.a. lead acid batteries
How does it work?
What happens when it is discharged? Recharged?

Answer 21

Uses two different oxidation states of Pb for its constitutive electrodes and sulfuric acid as electrolyte
When discharged (driving car
-> makes sense that this is the spontaneous path bc want natural/spontaneous current)
this is galvanic operation
-> fully charged lead batteries utilize Pbº as an anodic electrode and a PbO2 cathode, as the battery discharges, Pbº undergoes a two-electron oxidation to PbSO4, while PbO2 is reduced to the SAME species (so basically both half cells look like they have the same thing in them)

When recharge car -> this is electrolytic operation
Involves reversing the electron flow of discharge with applied voltage as an electrolytic cell

Diagram pg 276 helps visualize

Question 22

Overtime, a quanitity of e- can be used to do work such as electroplating
Given a current and time, the moles of e- transferred can be determined/moles of products of electrolysis

What is Faraday’s law of electrolysis? What does Faraday’s value indicate
equation?

Answer 22

Tells you the amount of ex. sodium metal and chlorine gas produced at the electrodes in the electrolytic cell

Can use this equation to get moles n:
I = nF/t
or use reasoning like below (and continue with stoichiometry until get grams)

Faraday’s law of electrolysis -> The amount of chemical change is proportional to the amount of electricity that flows through the cell
need to go over page 277 again but basically
1) find coulombs(charge) by Q=It equation
2) then use F to convert to moles of e- (bc F is C/mole of e-
3) then write out the half rxn, peep the BALANCED coefficient of e-, use stoichiometry to convert moles of sodium metal and chlorine gas to grams of each

Question 23

Alpha decay:

what does an alpha particle have? What happens during alpha decay? Dangerous?

Answer 23

Alpha particle has 2 protons and 2 neutrons and is equivalent to He (4 superscript, 2 subscript on left side of He)
reduced parent’s atomic number by 2 and mass number by 4
Wouldn’t say it is good for you, but does not travel as far and can be stopped by outer layer of skin

Question 24

Alpha decay:
what does an alpha particle have? What happens during alpha decay? Dangerous?
Atoms with ____ are most likely to undergo this type of decay process.

Answer 24

Alpha particle has 2 protons and 2 neutrons and is equivalent to He (4 superscript, 2 subscript on left side of He)
reduced parent’s atomic number by 2 and mass number by 4
Wouldn’t say it is good for you, but does not travel as far and can be stopped by outer layer of skin
The least dangerous type of ionizing radiation
Atoms with very large nuclei are most likely to undergo this type of decay process

Question 25

What is beta decay? 3 different types? Dangerous?
When MCAT mentions beta decay, which kind does it mean?
What is positron emission?

Answer 25

Each type of β decay is conversion of neutron into proton through action of nuclear weak force
β particles are more dangerous than alpha particle since particles since they are significantly less massive and can penetrate more
When MCAT mentions beta decay it means β -

3 types:
β - = when unstable nucleus contains too many neutrons (high n0/p+ ratios), it may convert a neutron into proton and an electron (also known as β- particle), which is ejected, daughter nucleus has a atomic number increased by 1, but mass number is the same (see equation sheet for what the beta thing looks like that is ejected

β + = positron emission, when nucleus contains too few neutrons (high p+/n0 ratios), it converts a proton into a neutron and a positron, which is ejected. The positron is the electrons antiparticle (same thing just different charge), the atomic number of the resulting daughter nucleus is 1 less than the radioactive parent nucleus, but the mass number remains the same.

Electron capture = capture e- from closest e- shell (n=1 shell) and use it in conversion of proton to neutron
Happens to nuclei with high p+/n0 ratios

Question 26

Gamma Decay

Dangerous? What is released?

Answer 26

Nucleus in excited state, accompanies most nuclear reactions -> which is usually the case after a nucleus has undergone alpha or any type of beta decay - can “relax” to its ground state by emitting energy in the form of one or more photons of electromagnetic radiation which are called gamma photons (VERY high freq and E)

Gamma decay dangerous! Only releases energy

Question 27

Nuclear reactions are endo/exothermic?
Nuclear Binding Energy and what equation is associated with it? Mass defect?
1eV = ______J

Answer 27

Nuclear reactions (decay, fission, fusion) are exothermic
ΔE = ΣBEparent - ΣBEdaughter
Eb = force holding nucleus together
Every nucleus that contains protons and neutrons has a nuclear binding energy which is the E that was released when the individual nucleons (P + N) were bound together by the strong force to form the nucleus. It’s also equal to the E needed to break up the intact nucleus into its individual nucleons.
When nucleons bind together to form a nucleus, some mass is converted to energy, so the mass of the combined nucleus is less than the sum of the masses of all its nucleons individually. The difference, delta m, is called the mass defect and its energy equivalent is the nuclear binding energy.
Δm = (total mass of separate nucleons) - (mass of nucleus) will always be positive

The nuclear binding energy Eb (J), can be found by Einstein’s equations of mass-energy equivalence:
Eb = Δmc^2
where c -> speed of light
1eV = 1.6 * 10^-19J

Question 28

When atom plutonium-239 is bombarded with an alpha particle, this element along with one free neutron is created:

a) Californium-240
b) Californium-241
c) Californium-242
d) Curium-242

Answer 28

C

page 86 in GChem book for answer explanation

Question 29

ALWAYS:
Cathode is where…
Anode is where…

Answer 29

Cathode is where...
reduction happens
plating happens
cations flow toward
current flow 

Anode is where...
oxidation 
pitting happens
anions flows toward
electrons flow from

Question 30

What can be produced in aqueous solution of electrolytic cell?

Answer 30

H2 or O2, etc

Question 31

What is the half reaction for Rh in RH2(SO4)3

Answer 31

Use oxidation state rules to write out the half reaction
Rh3+ + 3e- -> Rh(s)
This one’s a little tricky though

Question 32

longer/short half lives are safer than longer/shorter half-lives
Need to pass ___ half lives to be considered safe

Best way to solve a half life problem?

Answer 32

longer half lives are safer than shorter half-lives
Need to pass 10 half lives to be considered safe

Make table - 2 columns
first for time, second for quantity in % (so list 100%, 50%, 25%, 12.5%, 6%, etc) for questions that ask, how long does it take to reduce the amount of radioactive substance (t1/2 = 7 days) to 10% of its original amount

Question 33

Difference b/w electrochem and nuclear chem (particles involved, reversibility, reaction continues until…)

Answer 33

Electrochem -> e-, reversible, Ecell = 0V at equilibrium

Nuclear Chemistry -> neutrons, protons, beta = electrons, gamma = photon, no reversible, reach a stable nucleus