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IB Chem 3 > Topic 9: Redox Processes > Flashcards

Topic 9: Redox Processes Flashcards

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1
Q

Redox reactions always involve

A

transfer of e-

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2
Q

Oxidation is the____of electrons

A

Oxidation is Loss (OIL)

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3
Q

Reduction is the___of electrons

A

Reduction is Gain (RIG)

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4
Q

What is the ox state of an atom in elemental form?

A

0

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5
Q

What is the ox state of a mono or polyatomic ion?

A

For a monoatomic ion, ox state equals the charge. For a polyatomic, total ox states of all atoms must add to overall charge

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6
Q

Metals always have___(positive or negative) ox states in compounds

A

Positive

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7
Q

What is the table that determines priority for oxidation state? (Top of the table gets priority)

A

F= -1
H= +1
O= -2
7A= -1
6A= -2
5A= -3

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8
Q

What does the oxidizing agent do? What are some common oxidants?

A

It oxidizes the other substance, but it itself is reduced. Ex: halogens, ozone, manganate ions, hydrogen peroxide

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9
Q

What does the reducing agent do? What are some common reductants?

A

It reduces the other substance, but it itself is oxidized. Ex: H, C, CO, SO2

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10
Q

What is required for a metal to be oxidized in a redox reaction?

A

It must be more reactive than the oxidizing agent according to activity series.

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11
Q

What are the steps of balancing redox reactions in acidic conditions?

A

1) Identify ox states and which elements are reduced/oxidized
2) Make 2 half reactions, balance w/ respect to mass (elements other than O and H first, then balance O with H2O and H with H+)
3) Balance charge by adding e-
4) Make e- cancel out as you add equations together

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12
Q

What are the steps for balancing redox reactions in basic conditions?

A

1) Identify ox states and which elements are reduced/oxidized
2) Make 2 half reactions, balance w/ respect to mass (elements other than O and H first, then balance O with H2O and H with H+. Neutralize H+ by adding same amount of OH- to each side.)
3) Balance charge by adding e-
4) Make e- cancel out as you add equations together

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13
Q

Voltaic cells, AKA batteries, do what?

A

They generate electrical electricity from spontaneous redox reactions.

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14
Q

What happens at the anode and what charge is the anode for voltaic cells?

A

Anode=oxidation, negative

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15
Q

What happens at the cathode and what charge is the cathode for voltaic cells?

A

Cathode=reduction, positive

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16
Q

What is the purpose of the salt bridge?

A

To eliminate charge build up and complete the circuit. The anions in the salt bridge move from anode to cathode, and the cations from cathode to anode

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17
Q

What happens to the electrodes in a voltaic cell?

A

The anode goes into solution and loses e- as it is oxidized. The cathode has ions that come out of solution and increase the overall cathode mass as they are reduced.

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18
Q

Electrical current is driven by…

A

Potential difference: the difference between cell charges. The greater the difference, the stronger the current. Also driven by the flow of e- from oxidized to reduced substance

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19
Q

Potential difference is symbolized as…

A

E^0

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20
Q

What is the SHE cell?

A

Standard Hydrogen Electrode cell. This cell has E^0 value of 0 and acts as a reference point for all other half cells.

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21
Q

If a half-cell has a positive E^0 val, what does that mean?

A

It is more likely to be reduced than the SHE cell.

22
Q

If a half cell has a negative E^0 val, what does that mean?

A

It is more likely to be oxidized than the SHE cell.

23
Q

All E^0 values refer to the ____ reaction.

A

Reduction

24
Q

How do you determine which half cell will be reduced?

A

Half cell with higher reduction potential E^0 will be reduced.

25
Q

How do you calculate overall cell potential?

A

E^0 (cell) = E^0 (red) - E^0 (ox)

26
Q

What equation is used to determine spontaneity of redox reactions?

A

(Delta)G^0 = -n * F * (E^0 cell)
n is number of moles of e- transferred, F is Faraday’s constan

27
Q

How do you interpret change in G^0 and E^0 cell?

A

If E^0 is + and G^0 is -, reaction is spontaneous.
If E^0 is - and G^0 is +, reaction is nonspontaneous but reverse is spontaneous.
If both are equal to zero, reaction is at equilibrium.

28
Q

Give an example of electrochemical cell notation.

A

—->e- flow—–>—–>
Zn (s) / Zn 2+ (aq) // Cu 2+ (aq) / Cu (s)
Anode on left, salt bridge in middle, cathode on right

29
Q

What do electrolytic cells do?

A

They use an external energy source to drive an otherwise non-spontaneous reaction. They are not batteries, but they can use batteries. They can force a nonspontaneous reaction to happen

30
Q

What happens within an electrolytic cell?

A

The electrodes are place in elecrolyte, and connected to the battery with electrical wires. Ions from the electrolyte solution undergo ox/red. The power source causes the polarity of the cells to change.

31
Q

In electrolytic cells, what is the charge at the anode? Is this red or ox?

A

Anode is positive, oxidation.

32
Q

In electrolytic cells, what is the charge at the cathode? Is this red or ox?

A

Cathode is negative, reduction.

33
Q

In electrolytic cells, the anions move to the…

A

Anions go to anode.

34
Q

In electrolytic cells, cations move to the…

A

Cations go to cathode.

35
Q

How do you determine the products at the electrodes for an electrolytic cell?

A

Identify all ions (be sure to account for water for aqueous solutions) and use E^0 val to determine ox/red. Separate into half reactions, balance, add together.

36
Q

What happens during the electrolysis of NaCl (aq) for low concentrations?

A

If the concentration of NaCl is low, if Cl- is less than 25%, water will be favorably both reduced and oxidized while Na+ and Cl- will be spectator ions.

37
Q

What happens during the electrolysis of NaCl for high concentrations?

A

If Cl- is greater than 25%, Cl- will be oxidized instead of water, even though it has a higher reduction potential and is therefore less likely to be oxidized than water. Water is still reduced at the cathode.

38
Q

What is the equation for the oxidation of water?

A

2H20 (l) —> 4H+ (aq) + O2 (g) + 4e-

39
Q

What is the equation for the reduction of water?

A

2H20 (l) + 2e- —> H2 (g) + 2OH- (aq)

40
Q

What is the purpose of electroplating?

A

It plates metal onto an object at the cathode.

41
Q

What acronym can help you remember what happens at the anode/cathode?

A

An ox, red cat

42
Q

What acronym can help you remember what happens at the anode/cathode?

A

An ox, red cat

43
Q

In a voltaic cell, how do you determine which metal is oxidized or reduced?

A

More reactive metal is oxidized. Less reactive metal is reduced.

44
Q

What is oxidation state?

A

AKA ox number, it is the total number of e- that an atom gains or loses to form a chemical bond with another atom. It can be represented w/ a Roman numeral (copper (I) oxide) and it can help determine the reduced and oxidized species of a reaction.

45
Q

What is the activity series and how is it used for redox reactions?

A

It is a chart of metals in order of reactivity and reductant strength. More reactive metals are more readily oxidized. It is used to determine the product of single-displacement reactions

46
Q

In order for a single replacement reaction to take place between two metals, what is required? What makes a reaction like this faster?

A

The reductant metal must be more reactive than the oxidant metal. This determines whether or not a reaction will occur. Greater difference in reactivity makes the reaction faster

47
Q

What is a redox titration? What is it used for? What oxidants are usually used?

A

Titration of an oxidant by a reductant or vice versa. It is used to determine the concentration of an analyte containing an oxidant or reductant. The oxidant is usually potassium manganate (VII) or potassium dichromate (VI)

48
Q

In performing a redox titration for the following reaction, how would you determine the percent iron in an iron tablet?
Fe2+ —> Fe 3+ + e-

A

Fe2+ is oxidized. Calculate the moles of MnO4- needed to react with Fe2+ using n=cV, where V=volume and c=molarity. Then use the molar ratio to determine the moles of Fe2+ in solution. Calculate the mass of iron in the tablets using m=nM. Calculate percentage by mass of iron

49
Q

The electrodes in an electrolytic cell must be made from…

A

Inert, heat resistant material like graphite or platinum

50
Q

What are the two forms of energy flow in an electrolytic cell?

A

Current conducted by flow of e- in external part of the circuit, and the flow of cations toward cathode and anions toward anode

51
Q

How do you find the products of the electrolysis of a molten salt?

A

Write down the chemicals used. Create two half-equations for each chemical. Determine towards which electrode ions will flow. Combine the half reactions and check that the reaction is balanced.

52
Q

What are the five major differences between voltaic and electrolytic cells?

A

Voltaic: chem energy converted to electrical energy, exothermic, spontaneous rxn drives current, current conducted by e- and salt bridge ions, negative anode w/ positive cathode.
Electrolytic: electrical energy becomes chem energy, endothermic, electrical current drives nonspontaneous rxn, current conducted by e- and ions in electrolyte, positive anode w/ negative cathode

IB Chem 3 (11 decks)

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