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Chem 30 > Redox > Flashcards

Redox Flashcards

(93 cards)

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1
Q

What is the definition of ionic equations?

A

Ionic equations are written for reactions that involve substances that have an ionic nature (made of ions; E.g. acids and ionic compounds)

Ionic equations help to represent the actual chemical species involved in the reaction.

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2
Q

What is the purpose of writing net ionic equations?

A

Writing net ionic equations allows us to see what is actually happening by removing spectator ions

Spectator ions do not participate in the actual chemical change.

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3
Q

What are the three steps in writing net ionic equations?

A
  1. Write the molecular equation (M.E.)
  2. Re-write the equation showing all aqueous substances in dissociated form (total ionic equation, T.I.)
  3. Cancel all spectator species to obtain the net ionic equation (N.I.)
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4
Q

What must balance in a chemical reaction?

A

The charge of the reactant side must balance the charge on the product side

This is essential for the law of conservation of charge.

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5
Q

What is true about weak acids in ionic equations?

A

Weak acids ionize very little, so they should be kept in molecular form.

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6
Q

What do strong acids do in ionic equations?

A

Strong acids completely ionize and should be written in dissociated form.

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7
Q

How are solid metals represented in ionic equations?

A

Solid metals do not have a charge (they are atoms, not ions).

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8
Q

Do precipitates dissociate in ionic equations?

A

No, precipitates do not dissociate; check your solubility table.

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9
Q

What is electrochemistry?

A

Electrochemistry is the study of the relationship between chemical change and electrical work.

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10
Q

What type of reactions are involved in electrochemistry?

A

Electrochemistry involves reduction-oxidation reactions (redox reactions) which include electron transfer.

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11
Q

Give an example of a redox reaction.

A

Examples include:
* Burning wood
* Producing electricity in a battery
* Iron rusting
* Bleaching hair.

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12
Q

What does reduction mean in a theoretical definition?

A

A reaction in which atoms or ions gain electrons.

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13
Q

What is oxidation in a theoretical definition?

A

A reaction in which atoms or ions lose electrons.

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14
Q

What does the acronym LEO stand for?

A

LEO the lion goes GER: Loss of Electrons is Oxidation, Gain of Electrons is Reduction.

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15
Q

What types of reactions are generally considered redox?

A

Examples include:
* Formation reactions
* Decomposition
* Combustion
* Single replacement (always redox)
* Cellular respiration
* Photosynthesis.

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16
Q

What is an oxidizing agent?

A

An oxidizing agent causes oxidation by removing (gaining) electrons from another substance in a redox reaction and is reduced.

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17
Q

What is a reducing agent?

A

A reducing agent causes reduction by donating (losing) electrons to another substance in a redox reaction and is oxidized.

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18
Q

What indicates a spontaneous reaction?

A

A reaction is considered spontaneous if it occurs on its own.

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19
Q

How does a reduction half-reaction table help predict spontaneity?

A

It shows reduction half-reactions in the forward direction, indicating that all reactants will be oxidizing agents.

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20
Q

What is the strongest oxidizing agent (SOA)?

A

The species that is most likely to gain electrons.

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21
Q

What is the strongest reducing agent (SRA)?

A

The species that is most likely to lose electrons.

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22
Q

What happens if the oxidizing agent (OA) is higher in the table than the reducing agent (RA)?

A

The reaction is spontaneous.

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23
Q

What is a disproportionation reaction?

A

A reaction in which a species is both oxidized and reduced.

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24
Q

What is the first step in balancing acidic or basic redox reactions?

A

Write unbalanced half-reactions from the reaction given.

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25
What is the significance of oxidation numbers?
Oxidation numbers help identify redox reactions and can be used to balance them.
26
What is the operational definition of reduction historically?
Extracting metal from raw ore, where the mass of metal was less than the mass of mined ore.
27
What is the first step in balancing redox reactions using oxidation numbers?
Assign oxidation numbers, determine what is oxidized and reduced, or if it is not a redox reaction. ## Footnote Connect species using brackets.
28
How can you determine if a reaction is a redox reaction?
If any oxidation numbers of an element change, the reaction is a redox reaction.
29
What must be equal when balancing redox reactions?
The number of electrons lost must equal the number of electrons gained.
30
What is the role of coefficients in balancing redox reactions?
Coefficients are used to adjust the number of electrons lost and gained for each species involved.
31
What is the correct order for balancing remaining species in a redox reaction?
Start with redox species, then others, then balance H's and O's.
32
Fill in the blank: To balance oxygen in redox reactions, we can balance in _______ or _______ conditions.
[acidic] or [basic]
33
What does the endpoint indicate in a titration?
The point at which the indicator changes color permanently.
34
Define 'titrant' in the context of titrations.
The solution being added and its volume measured in the burette.
35
What is the equivalence point in a titration?
The point at which stoichiometrically equivalent amounts of reactants have been consumed.
36
What is a common oxidizing agent used in redox titrations?
MnO4-(aq) (permanganate)
37
In a voltaic cell, what is the role of the anode?
The anode is oxidized and is the source of electrons.
38
What is the relationship between the anode and cathode in terms of electron flow?
Electrons flow from anode to cathode.
39
What is the purpose of the salt bridge in a voltaic cell?
To maintain neutrality in both beakers by allowing ions to move between the half-cells.
40
Fill in the blank: An electrode that conducts electrons but does not react is called an _______ electrode.
[inert]
41
What is the significance of the potential difference in a voltaic cell?
It is the force that pushes electrons along the circuit, measured in volts.
42
What occurs when all Cu2+ ions are deposited onto the copper electrode in a voltaic cell?
The cell becomes 'dead' as the reaction reaches equilibrium.
43
What is the electrochemical cell notation for a cell made with Zn and Cu?
Zn(s) | Zn2+(aq) (1.0mol/L) || Cu2+(aq) (1.0mol/L) | Cu(s)
44
What does a standard electrochemical cell require?
Reactant and product ions must be present in concentrations of 1.0mol/L.
45
What happens to the mass of the anode in a voltaic cell?
The anode loses mass as it is oxidized.
46
What happens to the mass of the cathode in a voltaic cell?
The cathode gains mass as it is reduced.
47
What is the concentration of ions in the given electrochemical cells?
1.0 mol/L ## Footnote This concentration is standard for measuring cell potentials.
48
What are inert electrodes commonly made of?
* Carbon (graphite) * Platinum * Palladium ## Footnote Inert electrodes conduct electrons without participating in the reactions.
49
What happens at the anode in a voltaic cell?
Oxidation occurs ## Footnote Electrons are released from the anode.
50
What happens at the cathode in a voltaic cell?
Reduction occurs ## Footnote Electrons are accepted at the cathode.
51
What is the standard cell potential (Eocell)?
The potential difference between the electrodes of a voltaic cell under standard conditions ## Footnote Conditions include 1.0 mol/L concentration, 101.325 kPa, and 25.00 °C.
52
Fill in the blank: The voltmeter measures the _______ between the anode and cathode.
potential difference
53
What is the role of a voltmeter in an electrochemical cell?
Measures the potential difference between two points in a circuit ## Footnote This helps determine the voltage driving the electron flow.
54
What is the reduction half-reaction for copper?
Cu2+ + 2e- --> Cu(s) ## Footnote The standard reduction potential for this reaction is Eo = +0.34 V.
55
What is the oxidation half-reaction for zinc?
Zn(s) --> Zn2+(aq) + 2e- ## Footnote The standard oxidation potential for this reaction is Eo = +0.76 V.
56
True or False: A positive reduction potential indicates a negative oxidation potential.
True
57
What is a fuel cell?
A voltaic cell where reactants flow in and products flow out ## Footnote It functions like a rechargeable battery.
58
What is the primary waste product of fuel cells?
Pure water
59
What is corrosion?
A spontaneous reaction of materials with substances in their environment ## Footnote It often leads to structural integrity issues in metals.
60
What is rust composed of?
Hydrated iron (III) oxide (Fe2O3 * xH2O) ## Footnote The variable x represents the number of water molecules.
61
What is passivation in the context of corrosion?
The spontaneous formation of a hard non-reactive surface film that inhibits further corrosion ## Footnote This layer is typically an oxide.
62
What are two methods of corrosion prevention?
* Painting and coatings * Galvanizing ## Footnote These methods prevent air and water from accessing the metal.
63
What is cathodic protection?
A method to protect iron by making it the cathode of a voltaic cell ## Footnote This can involve sacrificial anodes or impressed current.
64
How is impressed current used in corrosion prevention?
By connecting a DC power source to provide electrons to the iron ## Footnote This protects the iron by preventing it from acting as an anode.
65
What is the standard potential of the hydrogen half-reaction?
0.00 V
66
What is the formula for calculating standard cell potentials?
Eocell = Eocathode - Eoanode
67
What happens to the anode's mass in a voltaic cell?
It may lose mass
68
What happens to the cathode's mass in a voltaic cell?
It may gain mass
69
What is the purpose of a sacrificial anode?
To protect a metal from corrosion by using a more reactive metal.
70
What do electrolytic cells convert?
Electrical energy into chemical energy.
71
What must the power source be for an electrolytic cell?
Direct current (DC).
72
What is the process in an electrolytic cell called?
Electrolysis.
73
What is the condition for a Voltaic cell to proceed?
The standard potential for the cell (Eo) must be positive.
74
In electrolysis, what happens to H2O in the presence of electricity?
It can be decomposed into hydrogen and oxygen gas.
75
What is the half-reaction for the reduction of water to hydrogen gas?
4H2O(l) + 4e- --> 2H2(g) + 4OH-(aq) Eο = -0.83V
76
What happens when salt is added to water during electrolysis?
It increases the rate of reaction.
77
What is the common salt used to increase the conductivity of water in electrolysis?
Na2SO4.
78
What is the charge of the cathode in an electrolytic cell?
Negative.
79
What is the charge of the anode in an electrolytic cell?
Positive.
80
How do the electrodes' charges differ in Voltaic and Electrolytic cells?
In Voltaic cells, the cathode is positive; in Electrolytic cells, the cathode is negative.
81
What is the first step in calculating the minimum voltage for an electrolytic cell?
List all species that can be oxidized.
82
What is the second step in calculating the minimum voltage for an electrolytic cell?
List all species that can be reduced.
83
What is the net reaction for the electrolysis of molten NaCl?
2Cl-(l) + 2Na+(l) --> Cl2(g) + 2Na(s).
84
What is overvoltage in the context of electrolytic cells?
An excess voltage required to drive a reaction beyond its predicted potential.
85
What happens to Cl- ions in an aqueous NaCl electrolytic cell?
They oxidize first before water is oxidized.
86
What are secondary batteries?
Batteries that can be recharged.
87
What is an example of a secondary battery?
Lead-acid car battery.
88
What is electroplating?
Coating an object with a thin layer of metal using electric current.
89
What is Faraday's Law in electrochemistry?
The amount of substance produced is related to the quantity of electricity applied.
90
What is the Faraday constant?
9.65 x 10^4 C/mol e-.
91
How is the charge transported calculated in a circuit?
By multiplying current (A) by time (s).
92
What is the relationship between moles of electrons and moles of deposited metal?
1 mole of electrons is needed to reduce each mole of metal ion.
93
What is the step-by-step method for calculating mass of deposited metal?
1. Calculate charge, 2. Calculate moles of e-, 3. Calculate moles of metal, 4. Convert to mass.

Chem 30 (3 decks)

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