Unit 3/4 Chemistry-Y12 REDOX Flashcards
REDOX-12THAUG TEST
1
Q
Oxidation can be identified by?
A
Gain in oxidation number
Loss of electrons
Gain of oxygen
Loss of hydrogen
2
Q
Reduction can be identified by ?
A
Loss in oxidation number
Gain of electrons
Loss of Oxygen
Gain of hydrogen
3
Q
In oxidation where are the electron in the redox half equation?
A
RHS.
4
Q
In reduction where are the electrons in the redox half equation?
A
LHS.
5
Q
Important Oxidation rules?
A
- Fluorine is always -1
- When hydrogen is bonded to non-metal it is +1, but when it bonded to metals it is -1.
- Oxygen is -2 in compounds, but in peroxides, it is -1 e.g. Na2o2.
- Group 7 elements are -1 but if 2 group 7 elements are present in a compound then the more electronegative one is the one that carries the -1.
6
Q
A electrochemical series compares and help us do?
A
It compares the relevant strength of oxidants and reductants and it helps us determine whether a reaction will occur spontaneously or not.
7
Q
What would be the impact of a failure of a salt bridge/ if it was removed/stopped working in a galvanic cell?
A
Without the salt bridge/ if it stops working/fails to work , the electron flow will not happen inside the galvanic cell, so it will not be able to generate electricity or the electric current.
8
Q
Oxidation always occurs at the?
A
Anode.
9
Q
Reduction always occurs at the?
A
Cathode.
10
Q
What is a galvanic cell?
A
A galvanic cell is a chemical system that produces an electric current (DC) from a spontaneous redox reaction.
11
Q
How to calculate cell potential?
A
E(cathode) - E(anode).
12
Q
what are the state symbols for the reactants that are molten ionic compounds in electrolytic cells?
A
Liquid.
13
Q
what are the state symbols for the products that are molten ionic compounds in electrolytic cells?
A
Liquid or gas.
14
Q
Why is an external power supply used in an electrolytic cell?
A
An external power supply is used to supply electrical energy to force a non-spontaneous chemical reaction to occur.
15
Q
What are the electrodes called in an electrolytic cell and what are the charges?
A
Anode which is +.
Cathode which is -.
16
Q
What are the electrodes called in a galvanic cell and what are the charges?
A
Anode which is -.
Cathode which is +.
17
Q
Electron flow is always?
A
From the anode to the cathode.
18
Q
Why is a mesh divider used in an electrolysis cell?
A
A mesh divider is used as some of the reactants might spontaneously react otherwise.
19
Q
Which type of cell uses a chemical reaction to produce electricity?
A
Galvanic cell.
20
Q
What part of a galvanic cell contains and inert electrolyte, and is necessary to complete the circuit and prevent build up of charge?
A
Salt bridge.
21
Q
EXAM Q: Draw and label the apparatus you could use in the laboratory for the electrolysis of molten potassium chloride?
A
electrolytic cell draw it and use book to mark it pg.49
22
Q
EXAM Q: List some industrial applications of electrolysis?
A
Electroplating, electrorefining and electrolysis of water.
23
Q
Describe the KOHES PROCESS not exam question but need to know to balance equations….
A
- Balance no. of electrons of the element that changes in oxidation no.
- Balance oxygen atoms by adding water.
- Balance hydrogen atoms by adding H+ ions.
- Balance charges on both sides by adding electrons to the more positive side.
- Add state symbols.
24
Q
Galvanic Vs Direct Contact
A
- Galvanic corrosion: Two different metals corrode in an electrolyte.
- Direct contact corrosion: Metals corrode from physical contact alone.
25
Draw a Danielle cell with (Zn and Cu) the zn and cu will remain the same if exam question is draw a Danielle cell
Daniell cell:
- draw a little wave of water IF THIS IS NOT THERE U WILL GET 0MARKS
- Anode is zinc. Anode half eq: zn(s)- zn2+ (aq) + 2e. Anode solution is zinc nitrate solution.
- Cathode is copper. Cathode half eq: cu2+(aq)+2e-- cu(s). Cathode solution is copper(II) nitrate solution.
- Salt bridge (K+) goes into the cathode and (NO3-) goes into the anode.
- Indicate that anode is zn(s) and cathode is cu(s) and point an arrow to the respective electrodes to show this.
- Eelectron flow from anode to cathode
- Label that Oxidation is at the anode and reduction is at the cathode.
26
Galvanic cell cathode+ or -?
- (+).
27
Galvanic cell anode+ or -?
- (-).
28
In oxidation, electrons are on the LHS OR RHS?
RHS.
29
In reduction, are electrons on the LHS OR RHS?
LHS.
30
In an electrolytic cell is the cathode + or -?
- (-).
31
In an electrolytic cell is the anode + or -?
- (+).
32
What part of the galvanic cell contains an inert electrolyte, and is necessary to complete the circuit and prevent the build-up of charge?
- The salt bridge.
33
Molten VS Aqueous/ solution: NaCl list the reactants for both molten and aqueous/solution.
- NaCl (l)/molten= Na+ and Cl-
- NaCl (aq)/solution= Na+, cl- and H2o.
34
When electroplating which electrode will the electroplated metal be deposited?
- Cathode.
35
Electrorefining is and example of?
- Is an example of purifying metals using electrolysis.
36
In electrorefining where would the pure and impure metal be?
- Pure is at cathode and impure is at anode.
37
Electrolytic cells what to include and draw it out.
Electrolytic cells:
- - draw a little wave of water IF THIS IS NOT THERE U WILL GET 0MARKS
- DC power supply and indicate if it is positive terminal + or – terminal on top of it
- Electron flow.
- Solution/ electrolyte in the middle of the cell should be (l) if molten or (aq) if in solution and solution would be the original compound that is being electrolysed.
- Anode half equation and cathode half equation.
- An arrow of e.g. x+ ions going to the cathode and z- ions to the anode.
- Electron flow.
- Oxidation at anode label and reduction at cathode label.
- A dash line to show the separator and indicate that it is the separator.
38
Anode always attracts the ?
- Anion.
39
Cathode always attracts the ?
- Cation.
40
Which side of the electrochemical series is the preferentially reduced and in what direction?
- Left side from bottom TO TOP
41
Which side of the electrochemical series is the preferentially oxidised and in what direction?
- RIGHT side from top to bottom
42
How to know if a substance will spontaneously react ?
- A spontaneous reaction will occur if the oxidant present is placed higher in the electrochemical series than the reductant present.
43
Modifications of standard galvanic cells are focused on?
- Increasing rate of forward reaction ( spontaneous reaction) while minimising the rate of the reverse reaction.
44
Ways to prevent the corrosion of iron?
- (Barrier), removing oxygen or water from the system.
- (Chemical), coating the iron with a more reactive metal e.g. zinc.
45
What does the key term " purification of metal" mean
That it is electrorefining.
46
In electroplating where is the impure metal located at?
- Anode.
47
In electroplating where is the object to be plated located at?
- Cathode.
48
What are the impurities at the bottom of anode in the process of electrorefining called?
- Anodic Sludge.
49
Does reductant strength increase or decrease across a period?
- Decreases.
50
How to answer the multiple choice question with elements (x,y,z) and they ask which is the strongest oxidant?
- The strongest oxidant is the most that reacts the most with the other metals/ is more readily reduced.
51
Identify the species that undergoes reduction?
- The (x2+) in mgx0cl3.
52
The decrease in the mass of one electrode was 3.5g. Calculate the increase in the mass of the other electrode?
1. Write half equation.
2. Fid no. of moles of anode by taking 3.5/ mr of anode.
3. Find molar ration and then find moles of cathode.
4. Mass of cathode.
53
A chemistry student performed an experiment to determine which factors affect the rate of corrosion of iron, as shown in the following diagram below. Corrosion of the first nail was most extensive in test tube 3 . No corrosion of the nail was observed in test tube 2. Suggest one reason why there was more corrosion of the nail in test tube 3 than in test tube 1.
- In test tube 3 the (insert solution) acts as a catalyst for the reaction.
54
A chemistry student performed an experiment to determine which factors affect the rate of corrosion of iron, as shown in the following diagram below. Corrosion of the first nail was most extensive in test tube 3 . No corrosion of the nail was observed in test tube 2. Explain why no corrosion was observed in test tube 2.
- Water is necessary for corrosion to occur, and water was removed from test tube 2.
55
Aluminium is extracted by the electrolysis of a molten mixture of aluminium oxide and cryolite. Oxygen is formed at the positive carbon electrodes. Explain why the positive carbon electrodes must be continually replaced, Include half equation.
- At very high temperatures the oxygen reacts with the carbon electrode so the positive electrode burns/wears away to produce carbon dioxide. C(s)+02(g)--->Co2(g).
56
A substance conducts electricity because if it has free moving , charged particles. What are the free moving charged particles in a Carbon electrode ( made from graphite).
- Delocalised electrons.
57
A substance conducts electricity because it has free moving , charged particles. What are the free moving charged particles in a Molten mixture of aluminium oxide and cryolite.
- Ions
58
A substance conducts electricity because if free moving , charged particles. What are the free moving charged particles in a Metal wire.
- Delocalised electrons.
59
What is the state of a precipitate?
Solid.
60
What is the different between total/complete ionic equation and net ionic equation.
In complete / total ionic equation you don't cancel out the ions on either side of the equation, whereas in net ionic equation you do.
61
What facilitates the flow of ions in corrosion and why?
Salt water because it has NaCl in it.
62
Salty waters can conduct electricity well, explain why might this be the case?
Salty water conducts electricity well because dissolved salt (e.g., NaCl) separates into sodium ions (Na⁺) and chloride ions (Cl⁻). These free-moving ions allow electrical current to pass through the solution.
63
Give two reasons why the electrochemical cell would eventually stop working.
- The reactants (oxidant or reductant) are fully consumed, so no further redox reactions can occur.
- The build-up of ions in the electrolyte prevents further electron flow, stopping the cell from generating electricity.
64
How to answer state the oxidizing / reducing agent?
- Pick the whole species e.g. H2S instead of saying h in h2s.
65
A strip of nickel is added into four test tubes containing aqueous solutions of different metal salts as shown in the diagram. In which test tube will a reaction occur . HOW TO ANSWER THIS QUESTION.
- use reactivity series to see which solutions are more or less reactive an then cancel the options out accordingly.
66
In industry, the electrodes are made from graphite ( carbon) and the carbon in the anode reacts spontaneously with oxygen gas at very high temperatures. Suggest a reason for the use of graphite electrodes, despite the need for regular replacement of then anodes.
1. B/c they have a high melting/ boiling point.
67
which of the following does not occur in the dissolution of compound X in water ... how to answer this question
Look for which option has the breaking of ionic bons of compound X.
68
1 mark, suggest one source of nitrogen oxides in the air in large enough quantites
- vehicle emissions from cars and trucks, especially those powered by internal combustion engines.
69
When exposed to oxygen in the air, a reactive metal will
Lose electrons and form a metal oxide.
70
When O2(g) is the reactant, it is always the
Oxidant.
71
Why don't we want a direct reaction
A direct reaction releases heat enegry instead of electricity as enegry.
- Separating half-reactions forces electron flow through a circuit, generating a usable current.
72
Why we want indirect reactions
Indirect reactions allow controlled electron transfer through an external circuit, converting chemical energy into electrical energy. This prevents energy loss as heat and enables practical applications like batteries.
73
Sentence structure to explain no spontaneous reaction ( in terms of a reductant)
RS is a weaker reductant than the conjugate reductant of OS which is (add stronger reductant), hence no spontaneous reaction will be observed.
IN TERMS OF A OXIDANT YOU JUST FLIP IT AROUND THE OTHER WAY.
74
If there is a change in temperature ( temp decreased) what are the potential impacts and observations
Reaction may not be observed as rate of reaction is to slow.
75
If the concentration is higher/lower than 1M what are the potential impacts and observations
Another product may form at an electrode.
No reaction may be observed if the concentration is too low.
76
If there are conditions/experimental designs what are the potential impacts and observations
Different voltage produced.
77
Salt bridge contains
electrolyte.
78
Ions are
Internal.
79
Electrons are
External.
80
A primary cell is
A cell that cannot be recharged.
81
Why is it better to use a graphite electrode rather than a graphite cell
A graphite electrode is preferred as it conducts electricity efficiently and allows controlled redox reactions, unlike a graphite cell, which lacks distinct anode and cathode regions.
82
Pure water lacks
Pure water lacks electrolyte, therefore no ions to complete internal circuit,
83
In a fuel cell the fuel always reacts at the
Anode.
84
In a fuel cell the oxygen always reacts at the
Cathode.
85
What electrodes do fuel cells make use of
Porous electrodes.
86
Why are porous electrodes better
porous=material with many holes=allow a greater surface area for reactions to take place=faster rate of reaction as compared to if a graphite electrode was used.
87
In a alkaline fuel cell what electrode do the OH- ions move towards
The OH- ions move towards the anode to facilitate in reaction.
88
What happens to the concentration OH- ions
In an alkaline fuel cell, the [OH⁻] concentration decreases at the anode because OH⁻ ions react with hydrogen to form water. However, at the cathode, OH⁻ is continuously produced as oxygen reacts with electrons and water.
89
What happens to H+ - ions in a fuel cell
In a fuel cell, H⁺ ions are produced at the anode when hydrogen gas (H₂) is oxidized. These H⁺ ions move through the electrolyte (such as a proton exchange membrane in a PEM fuel cell) to the cathode, where they react with oxygen (O₂) and electrons to form water (H₂O).
90
suggest one way in which a fuel cell differs from other galvanic cells
Fuel cells require a continuous supply of reactants, while in a galvanic cell it is stored in the cell.
91
What happens to oxide ions in a solid oxide fuel cell
In a solid oxide fuel cell (SOFC), oxide ions (O²⁻) are produced at the cathode when oxygen molecules (O₂) gain electrons. These oxide ions then move through the electrolyte to the anode, wher
92
List 3 advantages and 3 disadvantages of Fuel Cells
Advantages:
- High efficiency.
- Low emissions.
- Quiet operation.
Disadvantages:
- Expensive.
- Fuel supply needed.
- Durability issues.
93
Explain how fuel cells are more energy efficient than combustion reactions
Because they have less energy transformations than combustion reactions, thus they lose less energy and are more efficient.
94
When the cell begins to produce electricity, the pH of the electrolyte near the cathode increases and eventually reaches a constant value. Explain why this occurs ( For alkaline)
At cathode OH- ions are being produced, which increases concentration of OH- ion which results in an increase in pH near the cathode. Eventually the OH- ions migrate towards the anode in a stable CONCENTRATION of OH- ions which gives a constant pH.
95
When the cell begins to produce electricity, the pH of the electrolyte near the cathode increases and eventually reaches a constant value. Explain why this occurs ( For acidic)
- At the cathode, H⁺ ions are consumed, increasing their concentration.
- This decreases the pH near the cathode.
- Eventually, a stable concentration of H⁺ ions is reached, maintaining constant pH.
96
What does basic conditions refer to
It is same as alkaline conditions which means that OH- ions are present.
97
Why is large scale production of electricity using fuel cells suggested as a part if a solution to the greenhouse problem
Decreased energy transformation=increased efficiency=decreased/less net CO2 emissions per (g/kg) of fuel.
98
What comes under designing for efficiency
- Use of catalyst.
- Combined heat and power.
99
Renewable feedstocks for fuel cells include
Biofuels e.g. bioethanol.
100
List some examples of renewable fuel cells
- Bioethanol fuel cell.
- CO2/H2 fuel cell.
- Microbial fuel cell.
101
State the safety issues associated with the following ( H2(g), H+(aq) and OH-(aq))
- H2(g)= flammable.
- H+(aq)= corrosive.
- OH-(aq)= caustic.
102
Increase in OH- ion is equal to
Increase in OH- ion= more alkaline= increase in pH.
103
Increase in H+- ion is equal to
Increase in H+-ion = more acidic= decrease in pH.
104
Why is a carbon/graphite anode used instead of an (X) anode
Carbon (graphite) is inert and wont take part in the reaction, if (X) was used (X) would oxidise to (_).
105
Suggest one reason why the melting point is lowered in an electrolytic cell
- To reduce costs and reduce thus reduce energy.
106
Brine refers to
A concentrated salt solution e.g. NaCl.
107
What is anodic sludge made of/what would be expected to be found at the anodic sludge and why
- Gold and sliver.
- They are weak reductants also they dont get oxidised at the anode, instead they fall off the blister ( copper) and into the "mud" at the bottom.
108
In electroplating why do you need a constant supply of the metal at the anode
- A high concentration of metal at the anode ensures a steady supply of metal ions to the electrolyte.
- This maintains a consistent plating rate at the cathode during electroplating.
- It prevents the depletion of metal ions, which could disrupt the plating process.
109
When a cell is charging it is acting like a
Electrolytic cell.
110
When a cell is discharging it is acting like a
Galvanic cell.
111
Describe the key difference between a primary and a secondary cell
- Primary cell: Non-rechargeable.
- Secondary cell: Rechargeable.
112
What makes a secondary cell rechargeable
A secondary cell is rechargeable because its chemical reactions are reversible, allowing it to be restored by applying an external current.
113
If a spectator ion is in (aq) form you
If a spectator ion is in (aq) form you don't have to include it in your overall equation.
114
Define/how to look for independent and dependent variable
- Independent variable: The factor you change.
- Dependent variable: The factor you measure.
115
Explain why the experimental value of the voltage is different from the theoretical voltage
- Setup was not at SLC.
- Other reactions may have been occurring within the (_).
