Electrochemistry

Question 1

Shortcut to calculating oxidation state

Answer 1

More electronegative atoms get a -
Less electronegative atoms get a +
Sum the total bonding atoms.

Question 2

What is oxygen’s oxidation state trend?

Answer 2

Usually is -2 unless it’s a peroxide or molecular oxygen.

Peroxide is usually -1 while molecular oxygen is 0.

Question 3

What is hydrogen’s oxidation state trend?

Answer 3

Usually +1 unless it’s a hydride or molecular hydrogen.

Hydride is +1 and molecular hydrogen is 0.

Question 4

What’s the mnemonic for oxidation/reduction.

Answer 4

Red cat Leo goes Ger.

Reduction occurs at the cathode.
Loss of electrons is oxidation
Gain of electrons is reduction.

Question 5

How do you balance redox reactions?

Answer 5

1. Calculate each oxidation number and find the transfer of electrons.
2. Cross multiply the OPPOSITE amount of electrons.
3. Count the overall charge of each side and add H/OH as needed.
4. If it’s still not balanced, then add H2O as needed on either side to balance.

Question 6

Reduction NADH / NADPH

Answer 6

NADH reduces carbonyls

NADPH reduces alkene double bonds.

Question 7

Relate electron flow and electron affinity

Answer 7

Electrons flow from low electron affinity to high electron affinity.

Question 8

What are the oxidation potentials of the first two groups of the periodic table?

Answer 8

High oxidation emf.
Very negative reduction potential.
Group 1 is more reactive and oxidative than group 2.

Question 9

Relate precious metals and oxidation

Answer 9

Precious metals don’t oxidize easily and have a high reduction potential.

Question 10

What is the formula for calculating emf?

Answer 10

Emf = Ered + Eox

Question 11

Relate spontaneity and emf.

Answer 11

delta G(or work) = - neF

If E is negative is associated with a favorable reaction.
F = 96,500
n = number of electrons.

Question 12

Relate Oxidation and electrochemical cells

Answer 12

Oxidation occurs at the anode, electrons flow away from the anode.

Question 13

Relate Reduction and electrochemical cells

Answer 13

Reduction occurs at the cathode, electrons flow towards the cathode.

Question 14

Relate ions and the electrochemical cells

Answer 14

Anions go toward the anode

Cations go toward the cathode

Question 15

What is the significance of the salt bridge?

Answer 15

Anions flow in the direction opposite to the direction of the electron flow, in order to balance out the distribution of charge associated with moved electrons. The salt bridge completes the loop. Without a salt bridge, or some form of anion transfer, the circuit is incomplete and the cell could not produce energy.

Question 16

What is the standard line notation for electrochemical cells?

Answer 16

Reactant anode | product anode | reactant cathode | product cathode.

Question 17

Contrast Galvanic and electrolytic cells

Answer 17

Galvanic is spontaneous, which is a positive emf.

Electrolytic is nonspontanous, which is a negative emf.

Question 18

Describe a galvanic cell

Answer 18

Same thing as a voltaic cell.
Anode on the left, cathode on the right.
Over the life of the cell, the anode dissolves away and the cathode plates out.
Cathode positive, anode negative.

Question 19

Describe the electrochemical cell

Answer 19

Cathode on the left (-) , anode on the right (+)
Cathode plates the positive ion to the electrode.
Nonspontaneous, so it needs a battery.

Question 20

Describe voltaic cells over time

Answer 20

Eventually, the voltaic cell decreases in charge over time.

More are more energy, products are formed until it’s not favorable anymore. Therefore, more product means less voltage.

Question 21

What are the conceptual things to know about the nerst equation?

Answer 21

Use this when the reaction is NOT at standard state:

E cell = E* - [(.06/n) log Q]

If the Q is greater than 1, more products than reactants, then the value of E is less than at standard state.
If the Q is less than 1, more reactants than products, then the value of E is more than the standard state. As the reaction continues and more products are formed, then the Ecell decreases.

Question 22

Describe electrolysis

Answer 22

Basically an electrolytic cell. Cathode/reduction occurs on the right and anode/oxidation occurs on the left. Electrons move from anode to cathode. Cations move towards cathode and anions move toward anode to form gas.

Question 23

Voltage in electrochemistry

Answer 23

The voltage(emf) of a reaction is an intensive property so it won’t change if you add more moles.

Question 24

Describe concentration cells

Answer 24

Less concentrated loses electrons to be more concentrated (oxidation site)
Reduction occurs on the more concentrated side.

Question 25

What is the formula for E @ standard state?

Answer 25

E = .03logk / n

Log(k) = nE/ .06

If K is greater than 1 then E is positive making it favorable.
If K is less than 1 then E is negative making it not favorable.

Question 26

What is the standard emf of a concentration cell?

Answer 26

-Delta G = 0 if the concentration is balanced.