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

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2
Q

Reduction can be identified by ?

A

Loss in oxidation number
Gain of electrons
Loss of Oxygen
Gain of hydrogen

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3
Q

In oxidation where are the electron in the redox half equation?

A

RHS.

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4
Q

In reduction where are the electrons in the redox half equation?

A

LHS.

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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.
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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.

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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.

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8
Q

Oxidation always occurs at the?

A

Anode.

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9
Q

Reduction always occurs at the?

A

Cathode.

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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.

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11
Q

How to calculate cell potential?

A

E(cathode) - E(anode).

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12
Q

what are the state symbols for the reactants that are molten ionic compounds in electrolytic cells?

A

Liquid.

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13
Q

what are the state symbols for the products that are molten ionic compounds in electrolytic cells?

A

Liquid or gas.

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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.

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15
Q

What are the electrodes called in an electrolytic cell and what are the charges?

A

Anode which is +.
Cathode which is -.

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16
Q

What are the electrodes called in a galvanic cell and what are the charges?

A

Anode which is -.
Cathode which is +.

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17
Q

Electron flow is always?

A

From the anode to the cathode.

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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.

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19
Q

Which type of cell uses a chemical reaction to produce electricity?

A

Galvanic cell.

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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.

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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

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22
Q

EXAM Q: List some industrial applications of electrolysis?

A

Electroplating, electrorefining and electrolysis of water.

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23
Q

EXAM Q: State the method for the extraction of aluminum? NOT NEEDED

A
  • Treat bauxite with Naoh to remove impurities.
  • Dissolve the al2o3 in molten cryolite, the cryolite has a lower melting point
    than alumina ( 10009 deg compared to 2072 deg), which reduces operating
    costs.
  • Electrolyze using graGphite electrodes.

Oxidation half equation: 202-(l)->o2(g)+ 4e-
Side reaction: Co(l)+o2(g)–> Co2(g)

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24
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.
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25
Q

Galvanic Vs Direct Contact

A
  • Direct contact: oxidant and reductant react with one another and there is an electron transfer between them that cannot be detected. Energy is realised in the form of heat.
  • Galvanic cell: The electrons move from the reductant to the oxidant and are forced to travel along the external wiring to reach the oxidant. This can be detected by a voltmeter. This flow of electrons creates a direct electric current and thus the chemical energy of the reactants is transformed into heat energy.
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26
Q

Draw a Danielle cell with (Zn and Cu) the zn and cu will remain the same if exam question is draw a Danielle cell

A

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.

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27
Q

Galvanic cell cathode+ or -?

A
  • (+).
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28
Q

Galvanic cell anode+ or -?

A
  • (-).
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29
Q

In oxidation, electrons are on the LHS OR RHS?

A

RHS.

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30
Q

In reduction, are electrons on the LHS OR RHS?

A

LHS.

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31
Q

In an electrolytic cell is the cathode + or -?

A
  • (-).
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32
Q

In an electrolytic cell is the anode + or -?

A
  • (+).
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33
Q

What part of the galvanic cell contains an inert electrolyte, and is necessary to complete the circuit and prevent the build-up of charge?

A
  • The salt bridge.
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34
Q

Molten VS Aqueous/ solution: NaCl list the reactants for both molten and aqueous/solution.

A
  • NaCl (l)/molten= Na+ and Cl-
  • NaCl (aq)/solution= Na+, cl- and H2o.
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35
Q

When electroplating which electrode will the electroplated metal be deposited?

A
  • Cathode.
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36
Q

Electrorefining is and example of?

A
  • Is an example of purifying metals using electrolysis.
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37
Q

In electrorefining where would the pure and impure metal be?

A
  • Pure is at cathode and impure is at anode.
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38
Q

Electrolytic cells what to include and draw it out.

A

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.

39
Q

Anode always attracts the ?

A
  • Anion.
40
Q

Cathode always attracts the ?

A
  • Cation.
41
Q

Which side of the electrochemical series is the preferentially reduced and in what direction?

A
  • Left side from bottom TO TOP
42
Q

Which side of the electrochemical series is the preferentially oxidised and in what direction?

A
  • RIGHT side from top to bottom
43
Q

How to know if a substance will spontaneously react ?

A
  • A spontaneous reaction will occur if the oxidant present is placed higher in the electrochemical series than the reductant present.
44
Q

Modifications of standard galvanic cells are focused on?

A
  • Increasing rate of forward reaction ( spontaneous reaction) while minimising the rate of the reverse reaction.
45
Q

Ways to prevent the corrosion of iron?

A
  • (Barrier), removing oxygen or water from the system.
  • (Chemical), coating the iron with a more reactive metal e.g. zinc.
46
Q

What does the key term “ purification of metal” mean

A

That it is electrorefining.

47
Q

In electroplating where is the impure metal located at?

A
  • Anode.
48
Q

In electroplating where is the object to be plated located at?

A
  • Cathode.
49
Q

A student electrolyse a solution of substance (x) chloride with the intention of isolating substance (x).
Name the gas produced at the cathode and explain why this gas is produced , giving a reason as to why ( substance x) is not produced?

A
  • B/c H20 is preferentially reduced as it is a stronger oxidant as compared to substance x(ion), thus h2 is formed at the cathode as oxidation always happens at the cathode.
50
Q

What are the impurities at the bottom of anode in the process of electrorefining called?

A
  • Anodic Sludge.
51
Q

Does reductant strength increase or decrease across a period?

A
  • Decreases.
52
Q

How to answer the multiple choice question with elements (x,y,z) and they ask which is the strongest oxidant?

A
  • The strongest oxidant is the most that reacts the most with the other metals/ is more readily reduced.
53
Q

Identify the species that undergoes reduction?

A
  • The (x2+) in mgx0cl3.
54
Q

The decrease in the mass of one electrode was 3.5g. Calculate the increase in the mass of the other electrode?

A
  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.
55
Q

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.

A
  • In test tube 3 the (insert solution) acts as a catalyst for the reaction.
56
Q

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.

A
  • Water is necessary for corrosion to occur, and water was removed from test tube 2.
57
Q

One method that is used to prevent rusting is coating iron with zinc; this is known as galvanising. Galvanising iron creates a physical barrier that prevents rusting. Explain how the physical barrier prevents rusting.

A
  • Zinc coating forms a barrier to prevent iron from coming into contact with the atmosphere, Thus oxygen and water ( the reactants used in rusting reaction) do not come into contact with the iron, no reaction occurs
58
Q

Galvanising iron also prevents rusting by chemical means. Given that zinc is more reactive metal than iron, explain how galvanising prevents rusting by chemical means.

A
  • Zinc is a more reactive metal than iron so it will displace any iron ions form the solution. Thus if the zinc layer is damaged and the iron is exposed to the atmosphere, forming some iron ions, the zinc will displace these ions and cause the iron to reform and zinc ions to be formed.
59
Q

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.

A
  • 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).
60
Q

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).

A
  • Delocalised electrons.
61
Q

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.

A
  • Ions
62
Q

A substance conducts electricity because if free moving , charged particles. What are the free moving charged particles in a Metal wire.

A
  • Delocalised electrons.
63
Q

Steps for Writing a Complete/total Ionic Equation from a Molecular Equation.

A

Step 1: Break up each aqueous molecule into ions with the correct charge.
Step 2: Re-write the equation replacing aqueous molecules with ions.
Step 3: Write the correct coefficient before each ion to create a balanced complete ionic equation.

64
Q

What is the state of a precipitate?

A

Solid.

65
Q

Steps for writing a net ionic equation?

A

Step 1: Break up each aqueous molecule into ions with the correct charge.
Step 2: Re-write the equation replacing aqueous molecules with ions.
Step 3: Write the correct coefficient before each ion to create a balanced complete ionic equation.
Step 4: cancel out ions.
Step 5: Write equation with ions and then them making the precipitate which is solid.

66
Q

What is the different between total/complete ionic equation and net ionic equation.

A

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.

67
Q

What facilitates the flow of ions in corrosion and why?

A

Salt water because it has NaCl in it.

68
Q

Salty waters can conduct electricity well, explain why might this be the case?

A

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.

69
Q

why does ice float on water?

A

Ice floats on water because it is less dense than liquid water. When water freezes, its molecules form a crystalline structure with more open spaces, resulting in a lower density compared to liquid water.

70
Q

why is water such an important molecule for life on earth?

A

Water is essential for life because it acts as a universal solvent, facilitating biochemical reactions and transporting nutrients and waste within organisms.

71
Q

With increasing co2 emissions , what effect will this have on the acidity of our oceans?. Explain.

A

Increasing CO₂ emissions lead to higher levels of carbon dioxide in the atmosphere, which dissolves in ocean water forming carbonic acid. This process increases the acidity of the oceans, lowering the pH.

72
Q

How to calculate concentration of [ H+] when given pH?

A

(10^-pH) M

73
Q

Give two reasons why the electrochemical cell would eventually stop working.

A
  • 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.
74
Q

How to answer state the oxidizing / reducing agent?

A
  • Pick the whole species e.g. H2S instead of saying h in h2s.
75
Q

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.

A
  • use reactivity series to see which solutions are more or less reactive an then cancel the options out accordingly.
76
Q

Explain why aluminum cannot be obtained from the electrolysis of a seawater solution, Include relevant half equations.

A
  1. Include half equations.
  2. Aluminum cannot be obtained from the electrolysis of seawater as the h20 is preferentially reduced as oppose to the aluminum as it is a stronger oxidant.
77
Q

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.

A
  1. B/c they have a high melting/ boiling point.
78
Q

Using the following information what mass of water releases 2140 J of energy transitioning from liquid at 0 deg Celicus to ice at 0 deg Celicus. Latene heat of vapurisation = -44.0 kJ/mol. Latenet heat of fusion of water = -6.0 kJ/mol

A

To find the mass of water that releases 2140 J of energy as it transitions from liquid to ice at 0°C, you will use the formula:
q = m × L_f
Where:
- q is the heat energy released (2140 J),
- m is the mass of the water (unknown),
- L_f is the latent heat of fusion of water, given as -6.0 kJ/mol.

First, convert the latent heat of fusion to J/g:
L_f = -6.0 kJ/mol = -6000 J/mol

Since the molar mass of water is 18 g/mol:
L_f = (-6000 J/mol) ÷ (18 g/mol) = -333.33 J/g

Now, use the equation to solve for m:

2140 J = m × 333.33 J/g

m = 2140 J ÷ 333.33 J/g ≈ 6.42 g

So, the mass of water is approximately 6.42 g.

79
Q

which of the following does not occur in the dissolution of compound X in water … how to answer this question

A

Look for which option has the breaking of ionic bons of compound X.

80
Q

Draw two water molecules and clearly label the type of bonding present within and between the molecules

A
  • Covalent bond.
  • Hydrogen bond.
  • Dispersion forces also present.
  • slightly negative for oxygen.
  • slightly positive for hydrogen.
81
Q

What is meant by a weak acid?

A
  • It is not able to donate all of its [ H+ ] protons in water.
82
Q

1 mark, suggest one source of nitrogen oxides in the air in large enough quantites

A
  • vehicle emissions from cars and trucks, especially those powered by internal combustion engines.
83
Q

Based on its ka value is acid X a strong acid or a weak acid, explain. 1 mark…how to answer this question?

A
  • If Ka value is more than 1, this means the acid dissociates almost completely, indicating a strong acid.
  • If Ka value is less than 1, this means the acid only partially dissociates, indicating a weak acid.
84
Q

What is the Ka formula?

A

Ka= (final/ unknown concentration^2)/initial/known compound concentration of compound in solution.

85
Q

what is the pH of the resultant solution when 50.0ml of 0.034M sulfuric acid is mixed with 20mL of 0.124M sodium hydroxide….1 mark how to answer these questions

A
  • Calculate the moles of each reactant:
  • Determine the reaction and find the limiting reagent.
  • Calculate the remaining moles of the excess reagent.
  • Find the concentration of the remaining acid or base in the final solution.
  • Determine the pH: if it is acid then use pH= -log[H+] or if it is a base use pH=-LOG[OH-].
86
Q

How to calculate volume, number of moles, etc., if a gas is not at room temperature. State the formula and what the values mean.

A
  • PV=nRT
  • V= VOLUME.
  • n = NO. OF MOLES.
  • R=(8.31).
  • T= TEMPURATURE IN KELVIN SO IF IT IS IN DEG THEN YOU DO TEMP IN DEG+273.
  • P= pressure in kPA.
87
Q

List 3 sources of error of a titration.?

A

Parallax Error: Reading the burette from an angle can cause incorrect volume measurements.

End Point Error: Difficulty in spotting the exact end point can cause overshooting or undershooting.

Temperature Fluctuations: Temperature variations can affect the volume of the liquids and the reaction rate, potentially altering results.

88
Q

the total number of atoms in 5g of propane is?

A
  • Use N= n X Na
    Find no.of moles of propane in 5 g
    Times by Na/Avogadro’s constant 6.022 x 10^23
    times by the number of atoms in the molecule, so the formula of propane is c3h8, 3c+8h= 11 atoms, so times that by 11 and you will get 7.53 x 10^24 atoms.
89
Q

how to answer the question which of the following molecules will have the highest boiling point?

A

Check for Hydrogen Bonding:

Molecules with

𝑂
𝐻
−OH,

𝑁
𝐻
−NH, or

𝐹
𝐻
−FH bonds have the highest boiling points.
Compare Polarity:

More polar molecules (with dipole-dipole interactions) have higher boiling points than nonpolar ones.

Look at Size (Molecular Mass):

If IMFs are similar, the larger/heavier molecule will have a higher boiling point.

90
Q

The mass of one molecule of compound X in grams is?

A

Mr of compund X/ Avogardros constant.

91
Q

Oxidation of Secondary Alcohols to Carboxylic Acids

A
  • Conditions: Requires a strong oxidizing agent such as acidified potassium permanganate (KMnO₄)
  • Reaction: Secondary alcohol → Ketone (initial product) → Carboxylic acid under extended oxidation conditions.
92
Q

How do you convert mmHg to atm

A

To convert mmHg to atm, divide by 760 (1 atm = 760 mmHg)

93
Q

To convert from kPa to atm

A

Pressureinatm= kpa/101.3

94
Q
A