Electrochemistry

Question 1

What is the oxidation state of an element in its standard state

Answer 1

Zero

Question 2

What is the oxidation state of group 1 metals?

Answer 2

+1

Question 3

What is the oxidation state of group 2 metals?

Answer 3

+2

Question 4

What is the oxidation state of Fluorine?

Answer 4

-1

Question 5

What is the oxidation state of hydrogen?

Answer 5

+1 when bonded to an atom that is more electronegative than carbon

-1 when bonded to an atom that is less electronegative than carbon

0 when bound to carbon

Question 6

What is the oxidation state of oxygen? What is the exception?

Answer 6

-2

Exception is H₂O₂ , oxidation state is -1

Question 7

What are the oxidation states of the other halogens?

Answer 7

-1

Question 8

Reduction potentials are for the ____

Answer 8

Reactants

Li⁺ + e^- → Li

The reduction potential of Li⁺ is -3.05

Question 9

Stronger reducing agents have a stronger ____

Examples of strong reducing agents

Answer 9

Oxidation potential (more positive)

H₂, neutral metals, LiAlH₄, NaBH₄

Question 9

Stronger reducing agents have a stronger ____

Examples of strong reducing agents

Answer 9

Oxidation potential (more positive)

Look at products of reduction table

H₂, neutral metals, LiAlH₄, NaBH₄

Question 10

Stronger oxidizing agents have a _____

What are some examples of strong oxidizing agents

Answer 10

Stronger (more positive) reducing potential (look at reactants)

Neutral nonmetals (Oxygen, fluorine), MnO₄^-, CrO₃

(anything with a lot of oxygen is a strong oxidizing agent)

Question 11

How do you calculate cell potential? (E_cell)

Answer 11

E_cell = E_oxidation + E_reduction

Question 12

How is free energy related to the cell potential

Answer 12

They are inversely related

If E_cell > 0, Delta G < 0 = spontaneous

Question 13

In the electron transport chain, which will have the highest reduction potential?

Answer 13

Oxygen

Think of it as a competition for electrons, and the electrons will go to whichever has the highest (more positive) reduction potential

Question 14

If 2 amps are applied for 2 minutes, how many moles of Cu²⁺ will be plated out as Cu metal? (F = 96,500 C/mol)

Answer 14

120 seconds x 2 C/s x 1 mole e^-/ 100,000 C x 1 mol Cu/2 mol e^- = 1.2 x 10^-3 mole Cu

If asking for mass don’t forget to multiply by the molecular mass

Question 15

What must all cells consist of? (3 things)

Answer 15

Two or more electrodes made from a conductive material

An electrolyte bridging the gap between electrodes (salt bridge, aqueous solution w ions)

A circuit connecting the two electrodes

Question 16

Where does the electrochemistry happen in a cell?

Answer 16

At the electrode

Question 17

What is the difference between active and passive electrodes?

Answer 17

Active electrodes actively participate in electrochemistry. (Is oxidized or reduced)

Passive electrodes provide a surface for a substance but is not reduced or oxidized itself

Question 18

What provides the charge balance in a cell

Answer 18

The electrolyte

Question 19

What is the difference between Galvanic (Voltaic) and Electrolytic cells?

Answer 19

Galvanic cells have no external power source, are spontaneous (positive E_cell) and are discharging batteries

Question 20

In the decomposition of water, where do hydrogen and oxygen ions go?

Answer 20

Hydrogen ions go to the cathode (are reduced), oxygen ions go to the anode (are oxidized)

Question 21

How does plating occur?

What is the effect of plating?

Answer 21

Cations attack the cathode and become reduced

Plating is how you maintain the charge balance at the cathode

Question 22

Where do oxidation and reduction occur in a cell?

Answer 22

An Ox / Red cat

Oxidation always occurs at the anode, reduction always occurs at the cathode

Question 23

Where do oxidation and reduction occur in a cell?

Answer 23

An Ox / Red cat

Oxidation always occurs at the anode, reduction always occurs at the cathode

Question 24

How does pitting occur?

What is the effect of pitting?

Answer 24

When the anode is active, pitting occurs at the anode.

Pitting maintains the charge balance at the anode

Question 25

Cathode is where (6 things)

Answer 25

Reduction occurs

Current flows from (+ → -)

Electrons flow toward (- → +)

Cations flow toward

Plating occurs

Is positive in a galvanic cell and negative in an electrolytic cell

Question 26

Question: Which species will form at the anode?

How will you determine

Answer 26

Oxidation occurs at the anode

Look for species that has the greatest oxidation potential

Question 27

If copper is the anode and zinc is the cathode, which will have a more positive reduction potential?

Answer 27

Copper will have the more positive reduction potential

The anode will have a more positive reduction potential

Question 28

In a car battery, what occurs during galvanic operation?

Answer 28

The battery is being discharged

There is an increase in pH (Decrease in [H⁺])

A decrease in density

Question 29

What are the anode, cathode, and electrolyte in a charged cell car battery?

Answer 29

Anode = Pb - lead

Cathode = PbO₂

Electrolyte = H₂SO₄

Question 30

What are the anode, cathode, and electrolyte of an uncharged cell (Car battery)?

Answer 30

Anode = PbSO₄

Cathode = PbSO₄

Electrolyte = H₂SO₄

Question 31

What are the standard and actual cell potentials of a cell in equilibrium?

Answer 31

Standard = non-zero cell potential

Actual = 0 cell potential

Question 32

Alpha Decay

Answer 32

An alpha particle is emitted from the nucleus (He atom)

Atoms with large nuclei are most likely to undergo alpha decay

Least dangerous type of ionizing radiation (need a sheet of paper)

^4₂a

mass and atomic number are affected

Question 33

B^- decay

Answer 33

Neutron turns into a proton by emitting an electron

Happens in nuclei with high n:p ratios

Also called electron emission

₅₅Cs → ₅₆Ba

Question 34

Positron emission

Answer 34

Proton turns to a neutron

High p:n ratio

₁₁Na → ₁₀Ne

Question 35

Electron capture

Answer 35

Competes with positron emission

Both have high p:n ratios

₁₁Na → ₁₀Ne

Question 36

Gamma Decay

Answer 36

Most dangerous type of radiation

Emits just a photon, everything stays the same

Happens when a nuclei is in an excited state (relaxation process)

Question 37

Which is safer, compounds with longer or shorter half-lives?

Answer 37

Longer half-lives are safer than shorter half-lives

Usually need to pass 10 half-lives to be considered safe

Question 38

What kind of process is half-life?

Answer 38

1st order kinetics

½ life doesn’t change

Exponential decay

Question 39

Energy changes of nuclear reactions are ____

Answer 39

Exothermic, regardless of type (decay, fission, fusion)