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75 Cards in this Set

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the oxidation number of a free element
zero.
ex. 02, N2, S8 etc
the oxidation for a monatomic ion
is its charge
ex. Fe3+ =+3
F- = -1
The oxidation number of a group 1A element (alkali metals)
is +1
na, li etc

(H can be +1 or -1)
proton or hydride?
The oxidation of an alkali earth metal is
+2
Ca, Mg, Be
The oxidation number of a halogen is
-1 unless it is combined with a more electronegative element
ex. HCl vs HOCl
-1 with H (+1)
+1 with O (-2)
the oxidation number of hydrogen
-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
the oxidation of oxygen
(-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]-
What is the most common way to balance a redox reaction, why is balancing different/
-half reaction method ie. ion-electron method
-diff. because both conservation of charge and mass/stoich is important
overview of steps in the half reaction method
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
the oxidation number of a free element
zero.
ex. 02, N2, S8 etc
the oxidation for a monatomic ion
is its charge
ex. Fe3+ =+3
F- = -1
The oxidation number of a group 1A element (alkali metals)
is +1
na, li etc

(H can be +1 or -1)
proton or hydride?
The oxidation of an alkali earth metal is
+2
Ca, Mg, Be
The oxidation number of a halogen is
-1 unless it is combined with a more electronegative element
ex. HCl vs HOCl
-1 with H (+1)
+1 with O (-2)
the oxidation number of hydrogen
-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
the oxidation of oxygen
(-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]-
What is the most common way to balance a redox reaction, why is balancing different/
-half reaction method ie. ion-electron method
-diff. because both conservation of charge and mass/stoich is important
overview of steps in the half reaction method
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)
three types of cells
galvanic(voltaic), electrochemical and concentration
What types of electrochemical cells have spontaneous rxns occuring inside?
galvanic, voltaic (galv=volt), and concentration cells
which types of E cells need a battery or EMF source to run?
electrolytic cells
what is the same for all electrochemical cells?
an ox red cat for electrodes:
anode=electrode where oxidation occurs
cathode=electrode where reduction occurs
how do electrons move between electrodes?
anode to cathode

an ox red cat... same order as electron flow
Which direction is the current between electrodes?
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
what is an example of a galvanic/voltaic cell?
a regular battery.. makes sense that it would do work since this rxn is spontaneous (-delG, +EMF)
What is going on in the cell when a battery is dead?
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
for a galvanic or voltaic cell, the anode is +/- ?
The anode is negative
aneg is first (a first alphabetically, neg first alphabetically, galvanic cells were first)

a negative daniell
Why are half reactions separated into two chambers in voltaic/daniell/galvanic cells?
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.
Just e-s cannot flow because the equilibrium is electro-chem-ical. What is needed for both forces to equilibrate?
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
What are two common salts that make up the salt bridge?
KCl potassium chloride or
NH4NO3 ammonium nitrate

Both are inert strong electrolytes so they make good salt bridges
What is plating out? Where will it occur in an electrolytic cell?
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
for a metal, reduction leads to...
precipitation as a cation becomes a solid (reduction)
what is cell diagram notation?
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)
what is the order of components in a cell diagram?
anode| anode solution||cathode solution|cathode

left to right as the rxn proceeds
What is the cell diagram for a daniell cell (the one with Cu and Zn)

Hint: Cu is reduced
Cu is reduced=red cat at the cathode

anode| anode solution||cathode solution|cathode

Zn (s)| Zn2+(xM SO4,2-)||Cu2+|Cu(s)
for a galvanic cell the stuff on either side of the || line is...
in the same cup/chamber
give two examples of rxns in electrolytic cells
water--> h2 and O2

molten NaCl--> Na(l) + Cl2(g)
How is the appearance of an electrolytic cell different than that of a galvanic/voltaic cell?
-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)
What is the "regular" anode/cathode charge association (when EMF is positive)
An-neg
anode is negative,
cathode is positive.
Why is the anode (oxidized, loss of electrons) negative in a galvanic cell?
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
What is a daniell cell?
a common galvanic cell
Which is commonly the cathode?

cathode coat
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
lil mneumonic for cathode and anode in a normal cell
an-neg

cathode coat (reduction causes ion to bcm solid and coat the cathode)
cell diagram
anode| anode soln||cathode soln|cathode

|| = salt bridge or barrier

| = phase diff
electron flow between electrodes in a normal (galvanic/voltaic/concentration) vs. and electrolytic cell
normal: anneg, cathode coat

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

electrolyic cell:

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

what do anions and cations do?
anions to the anode(+) and cations to the cathode(-)
What does the faraday constant tell you?
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
How was the Faraday constant derived?
F=charge or an electron*# electrons/mole (avagadro's #)

1*10^5=(1.6*10^-19)*(6.022*10^23)
How is a concentration cell different from a galvanic cell?
the electrodes are made of the same material
What happens to the anode in a concentration cell at equilibrium>
It is erroded to make the chamber more concentrated

(Cu--> Cu2+ = oxidation), anox
What happens to a cathode in the concentration cell by equilibrium?
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
What is true of all the diagrams in the book?
cathode was on the right:

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

Where will ions migrate?
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)
SHE
Standard Hydrogen Electrode
Arbitrarily assigned 0V

H+ + 1e- ---> H is 0v (really H2)
reduction potential
The tendency of the species to gain electrons and become reduced
Standard reduction potentials are at
1M, 25*C (298K) and 1atm for any gas involved, metals in their pure state
Money metals
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)
If given two reduction potentials, how do you know what species will be oxidized and reduced?
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
EMF=

(by electrodes)
EMF= Ecathode-Eanode

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

(by reduction and oxidation potentials)
EMF=Ereduction+Eoxidation

(Eoxidation is really just the negative of the smaller less positive Ereduction)
Reduction potentials must never be
multiplied by stoich coefficients

the sign may have to be changed though depending on direction
The species with the higher reduction potential is the
cathode
the species with the lower (or negative) reduction potential is the
anode
If EMF is positive
dG is negative
dG=
-nFEcell

neg niffy
Change to transport a charge across a membrane
W=q(delV)
E*cell (@std. state)
-delG/ (nF)

del G=RTln(Keq)

E*=(-RTlnKeq)/nF
Ecell (not at std. state)
Ecell=E*cell- (RTlnQ/nF)
-nFE*cell=
-RTlnKeq
if Keq is less than one, Ecell is
negative

-nFE*cell=-RTlnKeq

natural log of a fraction is negative

natural log of 1+ is positive
if Keq is greater than one, Ecell is
positive (products are favored)

ln(1+) is positive

ln(fraction) is negative


-nFE*cell=-RTlnKeq
if K is equal to one,
delG=0
Ecell=0

because ln(1) =0
ln (1+)=
positive number, directly related to x
ln(fraction)=
negative number
ln(1)=
0