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MCAT - Chemistry > Class 6 > Flashcards

Class 6 Flashcards

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1
Q

What are the three ways you can identify reduction?

A
  1. Gaining electrons
  2. Losing bonds to more EN atoms
  3. Gaining bonds to less EN atoms
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2
Q

What are the three ways you can identify oxidation?

A
  1. Losing electrons
  2. Gaining bonds to more EN atoms
  3. Losing bonds to less EN atoms
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3
Q

When determining relative oxidation/reduction, does a double bond to oxygen count as “2 bonds”?

A

Yes

Count up number of oxygen bonds relative to hydrogen bonds. Pi bonds count twice

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4
Q

What are the 7 oxidation rules?

A
  1. The oxidation state of any element in its standard state is 0.
  2. 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.
  3. Group 1 metals have a +1 oxidation state, and Group 2 metals have a +2 oxidation state.
  4. Fluorine has a -1 oxidation state.
  5. 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.
  6. Oxygen has a -2 oxidation state.
  7. The rest of the halogens have a -1 oxidation state, and the atoms of the oxygen family have a -2 oxidation state.
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5
Q

Whats a simplistic way to think of the meaning of reduction potential?

A

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.

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6
Q

What is an approximation of reduction potentials?

A

Electronegativity. Increasing EN = increasing reduction potential

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7
Q

What do reducing agents do?

A
  1. Cause others to gain electrons
  2. They themselves are oxidized
  3. Have high oxidation potentials
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8
Q

What do oxidation agents do?

A
  1. Cause others to lose electrons
  2. They themselves are reduced
  3. Have very positive reduction potentials
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9
Q

What are common reducing agents?

A

H2
Neutral METALS
MEHx (LiALH4, NaBH4, etc.)

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10
Q

What are common oxidizing agents?

A

Neutral NONMETALS

MOx (MnO4-, CrO3, etc.)

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11
Q

Does a strong oxidizing agent have a high or low reduction potential?

A

High!

Conversely, a strong reducing agent will have a low reduction potential.

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12
Q

Free energy is inversely proportional to Ecell:

(delta)G = ?

A

(delta)G = -nFEcell

n= moles
F = constant
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13
Q

A _________ Ecell is a spontaneous reaction. Why?

A

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.

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14
Q

Ecell = ?

A

Ereduction + Eoxidation

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15
Q

Free energy is inversely proportional to Ecell:

(delta)G = ?

A

(delta)G = -nFEcell

n= moles
F = constant
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16
Q

A _________ Ecell is a spontaneous reaction. Why?

A

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.

17
Q

Ecell = ?

A

Ereduction + Eoxidation

18
Q

Electroplating:
Given a current and time the moles of electrons transferred can be determined:

I = ?

A

I = nF/t

F = Faraday's constant which will be given
n = mole of e- transferred
time = seconds!
19
Q

What three things must an electrochemical cell have in order to function?

A
  1. 2 or more electrodes made from conductive material
  2. An electrolyte bridging the gap between the electrodes (e.g. a salt bridge)
  3. A circuit to connect the two electrodes which can contain either a resistance or a power source
20
Q

What is a galvanic cell?

A

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

21
Q

If your current is flowing clockwise from positive terminal, what direction are the electrons flowing?

A

Counterclockwise from negative terminal

22
Q

What makes the positive terminal/electrode positive?

A

A build up of positive charges near or on it.

23
Q

An electrode is a CATHODE if ________ are flowing towards it.

A

CATIONS

24
Q

Something about a red cat and an ox pnemonic device?

A

look up

25
Q

What is an electrolytic cell?

A

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.

26
Q

What occurs at the cathode?

A

Reduction reactions
Current flows out of
Cations flow towards
Electroplating occurs here

27
Q

What occurs at the anode?

A

Oxidation reactions
Electrons flow out of
Anions flow towards
Electropitting occurs here

28
Q

What is an electrolytic cell?

A

Part of a circuit WITH an external power source

  • Non-spontaneous, negative Ecell
  • Rechargeable battery
29
Q

To recharge a battery do you use something with positive or negative potential?

A

Negative to GIVE the battery positive potential

30
Q

When recharging a battery where do the cations go?

A

Back into solution

31
Q

What is the only difference between a galvanic (non-rechargeable) and an electrolytic cell (rechargeable)?

A

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).

32
Q

What kind of cell will produce H2 from an aqueous solution?

A

Electrolytic cell

33
Q

What is Ce4+ and what is it good for?

A

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.

34
Q

What is the Nernst equation?

A

Eo = RT/nF lnK

35
Q

What kind of standard cell potential does a cell in equilibrium have? And actual cell potential?

A

Standard cell potential is non-zero

Actual cell potential is zero

MCAT - Chemistry (7 decks)

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