Genchem Stuff To Know

Front 1

the oxidation number of a free element

Back 1

zero.
ex. 02, N2, S8 etc

Front 2

the oxidation for a monatomic ion

Back 2

is its charge
ex. Fe3+ =+3
F- = -1

Front 3

The oxidation number of a group 1A element (alkali metals)

Back 3

is +1
na, li etc

(H can be +1 or -1)
proton or hydride?

Front 4

The oxidation of an alkali earth metal is

Back 4

+2
Ca, Mg, Be

Front 5

The oxidation number of a halogen is

Back 5

-1 unless it is combined with a more electronegative element
ex. HCl vs HOCl
-1 with H (+1)
+1 with O (-2)

Front 6

the oxidation number of hydrogen

Back 6

-1 with groups that are less electronegative than it (alkali earth metals and alkali metals)

ex. NaH, CaH...

Hydrides are important because they are really good reducers (ex. LiBH4)

+1 with more electronegative elements like halogens: HCl

Front 7

the oxidation of oxygen

Back 7

(-2) in most cases except:

*elemental (0)
*with F which is more electronegative (+2 in OF2)
*in peroxides it is -1 instead of -2, making it more reactive
(peroxide ion is [O--O]-

Front 8

What is the most common way to balance a redox reaction, why is balancing different/

Back 8

-half reaction method ie. ion-electron method
-diff. because both conservation of charge and mass/stoich is important

Front 9

overview of steps in the half reaction method

Back 9

1)separate into half reactions
2)balance the atoms of each half-rxn, use H2O and H+ freely to balance Os and Hs respectively
3)Balance the charges of each half reaction so the # of e-s can cross out
4) Add the half reactions
5)confirm that charge and mass are balanced

Front 10

the oxidation number of a free element

Back 10

zero.
ex. 02, N2, S8 etc

Front 11

the oxidation for a monatomic ion

Back 11

is its charge
ex. Fe3+ =+3
F- = -1

Front 12

The oxidation number of a group 1A element (alkali metals)

Back 12

is +1
na, li etc

(H can be +1 or -1)
proton or hydride?

Front 13

The oxidation of an alkali earth metal is

Back 13

+2
Ca, Mg, Be

Front 14

The oxidation number of a halogen is

Back 14

-1 unless it is combined with a more electronegative element
ex. HCl vs HOCl
-1 with H (+1)
+1 with O (-2)

Front 15

the oxidation number of hydrogen

Back 15

-1 with groups that are less electronegative than it (alkali earth metals and alkali metals)

ex. NaH, CaH...

Hydrides are important because they are really good reducers (ex. LiBH4)

+1 with more electronegative elements like halogens: HCl

Front 16

the oxidation of oxygen

Back 16

(-2) in most cases except:

*elemental (0)
*with F which is more electronegative (+2 in OF2)
*in peroxides it is -1 instead of -2, making it more reactive
(peroxide ion is [O--O]-

Front 17

What is the most common way to balance a redox reaction, why is balancing different/

Back 17

-half reaction method ie. ion-electron method
-diff. because both conservation of charge and mass/stoich is important

Front 18

overview of steps in the half reaction method

Back 18

1)separate into half reactions
2)balance the atoms of each half-rxn, use H2O and H+ freely to balance Os and Hs respectively
3)Balance the charges of each half reaction by adding electrons to the appropriate side
4)balance out the number of electrons per side by multiplying the whole half rxn by the appropriate number
5) Add half reactions and cross things out if on both sides (DEFINITELY e-s, maybe H+, H2Os)

Front 19

three types of cells

Back 19

galvanic(voltaic), electrochemical and concentration

Front 20

What types of electrochemical cells have spontaneous rxns occuring inside?

Back 20

galvanic, voltaic (galv=volt), and concentration cells

Front 21

which types of E cells need a battery or EMF source to run?

Back 21

electrolytic cells

Front 22

what is the same for all electrochemical cells?

Back 22

an ox red cat for electrodes:
anode=electrode where oxidation occurs
cathode=electrode where reduction occurs

Front 23

how do electrons move between electrodes?

Back 23

anode to cathode

an ox red cat... same order as electron flow

Front 24

Which direction is the current between electrodes?

Back 24

the current is opposite to the electron flow due to sign conventions

since e- flows anoxredcat (anode to cathode), I must flow cathode to anode

Front 25

what is an example of a galvanic/voltaic cell?

Back 25

a regular battery.. makes sense that it would do work since this rxn is spontaneous (-delG, +EMF)

Front 26

What is going on in the cell when a battery is dead?

Back 26

The half reactions have reached equilibrium.

delG is now zero (always zero at eq), so there is no more EMF and the battery is dead because current stops

Front 27

for a galvanic or voltaic cell, the anode is +/- ?

Back 27

The anode is negative
aneg is first (a first alphabetically, neg first alphabetically, galvanic cells were first)

a negative daniell

Front 28

Why are half reactions separated into two chambers in voltaic/daniell/galvanic cells?

Back 28

the point is to force electrons to travel through the wire in order to undergo the spontaneous redox reaction. If the solutions and electrodes were all in contact, the reaction would occur without doing any work.

Front 29

Just e-s cannot flow because the equilibrium is electro-chem-ical. What is needed for both forces to equilibrate?

Back 29

a wire for electrons (electro)
and a salt bridge for salts (chemical)

If there was no salt bridge, there would be a build up of negative charge wherever the electrons went

Front 30

What are two common salts that make up the salt bridge?

Back 30

KCl potassium chloride or
NH4NO3 ammonium nitrate

Both are inert strong electrolytes so they make good salt bridges

Front 31

What is plating out? Where will it occur in an electrolytic cell?

Back 31

Plating out is when a metal cation is reduced to a solid (red cat) at the cathode, so the solid forms on top of the cathode.
-this is how metal plating is done
-ex. Cu2+ +2e- -->Cu (s)
this is reduction
reduction happens at the cathode
the cathode is plated

Front 32

for a metal, reduction leads to...

Back 32

precipitation as a cation becomes a solid (reduction)

Front 33

what is cell diagram notation?

Back 33

shorthand for all the components in the cell with single indicating phase boundary (electrode vs solution) and double lines indicating a physical boundary (chamber separation or a salt bridge b/w chambers)

Front 34

what is the order of components in a cell diagram?

Back 34

anode| anode solution||cathode solution|cathode

left to right as the rxn proceeds

Front 35

What is the cell diagram for a daniell cell (the one with Cu and Zn)

Hint: Cu is reduced

Back 35

Cu is reduced=red cat at the cathode

anode| anode solution||cathode solution|cathode

Zn (s)| Zn2+(xM SO4,2-)||Cu2+|Cu(s)

Front 36

for a galvanic cell the stuff on either side of the || line is...

Back 36

in the same cup/chamber

Front 37

give two examples of rxns in electrolytic cells

Back 37

water--> h2 and O2

molten NaCl--> Na(l) + Cl2(g)

Front 38

How is the appearance of an electrolytic cell different than that of a galvanic/voltaic cell?

Back 38

-there will be a battery (by def electrolytic cells preform non spontaneous rxns, so EMF input is neccessary (for example a galvanic cell!)
-It all happens in one container (because there is no reason to separate reactants that are stable as is)

Front 39

What is the "regular" anode/cathode charge association (when EMF is positive)

Back 39

An-neg
anode is negative,
cathode is positive.

Front 40

Why is the anode (oxidized, loss of electrons) negative in a galvanic cell?

Back 40

because electrons keep leaving through the anode, making the electrode relatively positive. This causes all the positive ions from the solution to gather at the electrode, making it negative

Front 41

What is a daniell cell?

Back 41

a common galvanic cell

Front 42

Which is commonly the cathode?

cathode coat

Back 42

the one that gets plated and reduced.

This is often a money metal because money metals have the most positive (in EMF) reduction potentials.

cathode-Cu-Coat

Front 43

lil mneumonic for cathode and anode in a normal cell

Back 43

an-neg

cathode coat (reduction causes ion to bcm solid and coat the cathode)

Front 44

cell diagram

Back 44

anode| anode soln||cathode soln|cathode

|| = salt bridge or barrier

| = phase diff

Front 45

electron flow between electrodes in a normal (galvanic/voltaic/concentration) vs. and electrolytic cell

Back 45

normal: anneg, cathode coat

e- flow from anode to cathode (- to +)

electrolyic cell:

e- flow is from anode to cathode (+ to -) NOT spontaneous

Front 46

electrolytic cells:

what do anions and cations do?

Back 46

anions to the anode(+) and cations to the cathode(-)

Front 47

What does the faraday constant tell you?

Back 47

It bridges the electro and chem parts quantitatively:

For every mole of e-s transferred, 1*10^5 Columbs are moved, or 1*10^5 joules/volt

Front 48

How was the Faraday constant derived?

Back 48

F=charge or an electron*# electrons/mole (avagadro's #)

1*10^5=(1.6*10^-19)*(6.022*10^23)

Front 49

How is a concentration cell different from a galvanic cell?

Back 49

the electrodes are made of the same material

Front 50

What happens to the anode in a concentration cell at equilibrium>

Back 50

It is erroded to make the chamber more concentrated

(Cu--> Cu2+ = oxidation), anox

Front 51

What happens to a cathode in the concentration cell by equilibrium?

Back 51

As before, the cathode is plated (cathode coat)

This allows the concentration of CuSo4 to decrease and equilibrate with the anode's side

(Cu2+--> Cu =reducation), redcat

Front 52

What is true of all the diagrams in the book?

Back 52

cathode was on the right:

*more concentrated copper sulfate in concentration cell
*Na+-->Na in electrolytic cell
*Cu2+-->Cu in galvanic cell

Front 53

electrophoresesis:

Where will ions migrate?

Back 53

ANions (acidic) to ANode

CATions(basic) to CAThode

THis is because the electrophoresis set-up is an electrolytic cell (plug it into a power source)

Front 54

SHE

Back 54

Standard Hydrogen Electrode
Arbitrarily assigned 0V

H+ + 1e- ---> H is 0v (really H2)

Front 55

reduction potential

Back 55

The tendency of the species to gain electrons and become reduced

Front 56

Standard reduction potentials are at

Back 56

1M, 25*C (298K) and 1atm for any gas involved, metals in their pure state

Front 57

Money metals

Back 57

Are likely to be a cathode in the regular reactions (galvanic cell)

Cathode will be plated


we do not want money metals (copper, platinum, silver, gold) to dissolve in solutions! (be oxidized)

Front 58

If given two reduction potentials, how do you know what species will be oxidized and reduced?

Back 58

the one with the more positive reduction potential will be reduced, the other species will be forced to be oxidized because it is net spontaneous

Front 59

EMF=

(by electrodes)

Back 59

EMF= Ecathode-Eanode

like always with a normal cell, anode is negative! We can remember this negative sign.

Front 60

EMF=

(by reduction and oxidation potentials)

Back 60

EMF=Ereduction+Eoxidation

(Eoxidation is really just the negative of the smaller less positive Ereduction)

Front 61

Reduction potentials must never be

Back 61

multiplied by stoich coefficients

the sign may have to be changed though depending on direction

Front 62

The species with the higher reduction potential is the

Back 62

cathode

Front 63

the species with the lower (or negative) reduction potential is the

Back 63

anode

Front 64

If EMF is positive

Back 64

dG is negative

Front 65

dG=

Back 65

-nFEcell

neg niffy

Front 66

Change to transport a charge across a membrane

Back 66

W=q(delV)

Front 67

E*cell (@std. state)

Back 67

-delG/ (nF)

del G=RTln(Keq)

E*=(-RTlnKeq)/nF

Front 68

Ecell (not at std. state)

Back 68

Ecell=E*cell- (RTlnQ/nF)

Front 69

-nFE*cell=

Back 69

-RTlnKeq

Front 70

if Keq is less than one, Ecell is

Back 70

negative

-nFE*cell=-RTlnKeq

natural log of a fraction is negative

natural log of 1+ is positive

Front 71

if Keq is greater than one, Ecell is

Back 71

positive (products are favored)

ln(1+) is positive

ln(fraction) is negative


-nFE*cell=-RTlnKeq

Front 72

if K is equal to one,

Back 72

delG=0
Ecell=0

because ln(1) =0

Front 73

ln (1+)=

Back 73

positive number, directly related to x

Front 74

ln(fraction)=

Back 74

negative number

Front 75

ln(1)=

Back 75

0