Class 6 Flashcards
What are the three ways you can identify reduction?
- Gaining electrons
- Losing bonds to more EN atoms
- Gaining bonds to less EN atoms
What are the three ways you can identify oxidation?
- Losing electrons
- Gaining bonds to more EN atoms
- Losing bonds to less EN atoms
When determining relative oxidation/reduction, does a double bond to oxygen count as “2 bonds”?
Yes
Count up number of oxygen bonds relative to hydrogen bonds. Pi bonds count twice
What are the 7 oxidation rules?
- The oxidation state of any element in its standard state is 0.
- The sum of oxidation states of the atoms in a neutral molecule must always be 0, and the sum of the oxidation states of the atoms in an ion must always equal the ion’s charge.
- Group 1 metals have a +1 oxidation state, and Group 2 metals have a +2 oxidation state.
- Fluorine has a -1 oxidation state.
- Hydrogen has a +1 oxidation state when bonded to something more EN than carbon and a -1 oxidation state when bonded to something less EN than carbon. It has a 0 ox state when bonded to carbon.
- Oxygen has a -2 oxidation state.
- The rest of the halogens have a -1 oxidation state, and the atoms of the oxygen family have a -2 oxidation state.
Whats a simplistic way to think of the meaning of reduction potential?
How “much” some species wants to gain electrons. Negative potential (volts) means the species does NOT want electrons. Increasingly positive reduction potentials means species DO want electrons.
What is an approximation of reduction potentials?
Electronegativity. Increasing EN = increasing reduction potential
What do reducing agents do?
- Cause others to gain electrons
- They themselves are oxidized
- Have high oxidation potentials
What do oxidation agents do?
- Cause others to lose electrons
- They themselves are reduced
- Have very positive reduction potentials
What are common reducing agents?
H2
Neutral METALS
MEHx (LiALH4, NaBH4, etc.)
What are common oxidizing agents?
Neutral NONMETALS
MOx (MnO4-, CrO3, etc.)
Does a strong oxidizing agent have a high or low reduction potential?
High!
Conversely, a strong reducing agent will have a low reduction potential.
Free energy is inversely proportional to Ecell:
(delta)G = ?
(delta)G = -nFEcell
n= moles F = constant
A _________ Ecell is a spontaneous reaction. Why?
Positive because Ecell and (delta)G are related by a neg 1 coefficient, so you want a +Ecell to get a - delta G for spontaneity.
Ecell = ?
Ereduction + Eoxidation
Free energy is inversely proportional to Ecell:
(delta)G = ?
(delta)G = -nFEcell
n= moles F = constant
A _________ Ecell is a spontaneous reaction. Why?
Positive because Ecell and (delta)G are related by a neg 1 coefficient, so you want a +Ecell to get a - delta G for spontaneity.
Ecell = ?
Ereduction + Eoxidation
Electroplating:
Given a current and time the moles of electrons transferred can be determined:
I = ?
I = nF/t
F = Faraday's constant which will be given n = mole of e- transferred time = seconds!
What three things must an electrochemical cell have in order to function?
- 2 or more electrodes made from conductive material
- An electrolyte bridging the gap between the electrodes (e.g. a salt bridge)
- A circuit to connect the two electrodes which can contain either a resistance or a power source
What is a galvanic cell?
A cell with no external power source (needed)!
- Spontaneous, positive Ecell
- Discharging battery
- Has many other names such as voltaic
As it discharges, Ecell decreases/approaches 0
If your current is flowing clockwise from positive terminal, what direction are the electrons flowing?
Counterclockwise from negative terminal
What makes the positive terminal/electrode positive?
A build up of positive charges near or on it.
An electrode is a CATHODE if ________ are flowing towards it.
CATIONS
Something about a red cat and an ox pnemonic device?
look up
What is an electrolytic cell?
Part of a circuit WITH an external power source
- Non-spontaneous, negative Ecell
- Rechargeable battery
Flow is backwards from the galvanic cell because the electrolytic cell is being RECHARGED by an introduced power source.
What occurs at the cathode?
Reduction reactions
Current flows out of
Cations flow towards
Electroplating occurs here
What occurs at the anode?
Oxidation reactions
Electrons flow out of
Anions flow towards
Electropitting occurs here
What is an electrolytic cell?
Part of a circuit WITH an external power source
- Non-spontaneous, negative Ecell
- Rechargeable battery
To recharge a battery do you use something with positive or negative potential?
Negative to GIVE the battery positive potential
When recharging a battery where do the cations go?
Back into solution
What is the only difference between a galvanic (non-rechargeable) and an electrolytic cell (rechargeable)?
In an electrolytic cell the cathode is NEGATIVE
In a galvanic cell the cathode is POSITIVE
(Remember that galvanic cells are “normal” and the electrolytic cell is the opposite).
What kind of cell will produce H2 from an aqueous solution?
Electrolytic cell
What is Ce4+ and what is it good for?
A powerful oxidizing agent that is commonly used in redox titrations.
Ce4+ is yellow and turns to Ce3+ when it picks up an electron and turns colorless.
What is the Nernst equation?
Eo = RT/nF lnK
What kind of standard cell potential does a cell in equilibrium have? And actual cell potential?
Standard cell potential is non-zero
Actual cell potential is zero
