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Chemistry (A2) > Electrochemistry > Flashcards

Electrochemistry Flashcards

1
Q
A

Answer is A

Although equation 1 is oxidised and needs to be flipped it’s emf still stays the same

E(right) - E(left) = Emf

= 0.34 - -0.44 = 0.78

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2
Q

What happens when you dip a rod of a metal into its own ions

A

An equilibrium is set between the solid metal and aqueous metal ions

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3
Q

Write the half equation for Zinc (s) to Zinc (ii)

A
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4
Q

What is the simplest salt bridge made of

A

Filter paper soaked in a saturated solution of KNO3

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5
Q

Why are salt bridges necessary

A

To complete the circuit by allowing ion movement between the half cells to balance the charges, without reacting with the electrodes or aqueous metal ions within each half cell

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6
Q

What does a ______ Represent

1) |
2) ||

A

1) Phase change (solid liquid gas)
2) Salt bridge

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7
Q

How would an aluminium copper cell be represented

A
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8
Q

In electrochemistry what happens at the left hand electrode

A

Left hand electrode is where oxidisation occurs
Left hand electrode is the half cell with the most negative E Cell value

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9
Q

In electrochemistry what happens at the right hand electrode

A

Right hand electrode is where reduction occurs
Right hand electrode is the half cell with most positive e cell

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10
Q

Draw the standard hydrogen Electrode

A
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11
Q

What conditions is the standard hydrogen electrode used in

A

Temperature = 298K
Pressure = 100KPA
[H+] = 1 MOLDM^-3

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12
Q

What is the standard hydrogen electrode used for

A

Universal standard for the Comparing of other cells against the E Cell of the standard hydrogen electrode

E cell of standard hydrogen electrode e= OV

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13
Q

Why might the standard electrode not be used

A

Cheaper to use another comparison then the SHE

As SHE has platinum

Provides just as a good reference

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14
Q

If an E Cell is more negative what does it mean

A

Better reducing agent (easier to oxidise)

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15
Q

If an E Cell is more positive what does it mean

A

Better oxidising agent (Easier to reduce)

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16
Q

What factors alter E Cell value

A

Concentration of ions

Temperature

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17
Q

What happens if you reduce the concentration of the ions in the left hand half cell

A

Equilibrium moves to the left to oppose the change of removing ions (in reduced form)

This releases more electrons

the E Cell of the left hand cell becomes more negative

So EMF increases

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18
Q

How do you calculate the emf from e cell value

A

E Cell = ERight - ELeft

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19
Q

When would you use a platinum electrodes

Why is it chosen

A

When both oxidised and reduced forms
of the metal are in aqueous solution (no solids)

Inert and a good conductor

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20
Q

How would you predict if a reaction would occur

A

Take 2 half equations

Find species that is being reduced (RHS electrode)

Calculate its e cell - the e cell of the oxidised species

If E Cell > 0 reaction will occur

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21
Q

What is the Daniel Cell made from

A

Zinc/Copper(II)

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22
Q

What is the cell for disposable batteries made from

A

Zinc/Carbon

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23
Q

What reactions take place in a disposable battery

A

2NH4+ + 2e- ——> 2NH3 + H2

24
Q

What reactions occur in a lead acid batter (Car Battery)

25
What reactions occur in Nickel/Cadmium Cell Electrodes (AA Batteries)
(1st one is at net electrode)
26
What reactions occur on discharge in Lithium Ion Cells
27
What is a Fuel Cell?
A Chemical Cell that is used to generate electrical current but does not require electrical charging a constant supply of a fuel is needed
28
What are the Reactions that take place at the two electrodes in an alkaline fuel cell
29
Draw a diagram of a hydrogen fuel cell
30
Why is it better to use a fuel cell then to burn H2 in air Even if the same reaction occurs
Combustion requires higher temperatures Sulphur containing compounds (SO2,SO3) and nitrogen containing compounds (NOx,NO2) are produced due to the sulphur and nitrogen within the atmosphere and high temperatures These are pollutants Fuel Cells are more efficient
31
What are the Disadvantages to hydrogen fuel Cells
Hydrogen is a flammable gas with a low boiling point —> Hard, dangerous and expensive to store and transport as pressurised containers are needed Energy is required to form the hydrogen and oxygen in the first place. Fossil fuels are used to pass water through an electrolysis process. This contributes to CO2
32
What are the Advantages to Fuel cells
More efficient then ICE, more energy converted to kinetic then thermal store Fuel cells don’t require to be charged unlike EV’s Only waste product is water
33
How do you find the weakest reducing agent
Most positive E Cell value Product of the reduced form This reaction has the highest tendency to gain electrons, a reducing agent must loose electrons in an attempt to reduce a substance. Therefore it is the weakest
34
How do you find the Weakest Oxidising agent
Most Negative E Cell value Reactant of the reduced form This reaction has the highest tendency to loose electrons, a oxidising agent gains electrons in an attempt to oxidise a substance. Therefore the oxidising agent gains the least amount of electrons Weakest
35
How do you find the most powerful oxidising agent
Most positive E Cell value Reactant of the reduced form This reaction has the highest tendency to gain electrons, a oxidising agent must gain electrons in an attempt to reduce a substance. Therefore it is the strongest
36
How do you find the most powerful reducing agent
Most negative E Cell value Product of the reduced form This reaction has the highest tendency to loose electrons, a reducing agent must loose electrons in an attempt to reduce a substance. Therefore it is the Strongest.
37
What is the reason some cells cannot be reachrged
The reaction of the cell isn’t reversible, products cannot be converted back into reactants
38
How can the emf of a cell be kept constant
Reagents are supplied constantly so the concentrations of ions are constant Hence the electrode potential difference (E Cell( between the cells is the same
39
What is the overall Equation of discharge in a lithium ion cell? Negative Electrode = -3.04 v Positive Electrode= +0.56v What is the E Cell
0.56 (Right) — -3.04(Left) = 3.60v
40
What reactions occur at a acidic hydrogen oxygen fuel cell?
41
What is the emf of an acidic and alkaline hydrogen oxygen fuel cell
1.23v
42
What does Acidify mean
Reduced, gained electrons
43
A List of electrode Potentials (E Cell) in Numerical Order
44
From the Table Below Write an Equation for the reaction between VO2 + and iron to form VO (2+)
45
Non Standard Conditions
46
47
How do you maintain a Constant Emf in a Fuel Cell
Reactants must be constantly supplied at the same rate
48
49
Stage 1: Creation of 1 MolDm^-3 of TIO^2+ 0.5 moldm^-3 of H2SO4 in 50ml = 0.05moldm^-3 of H+ ions Therefore 0.05X159.9 = 7.995g needs to be weighed of TiOSO4 And added to the Sulphuric Acid Transfer to Volumetric Flask and make up to mark Stage 2: Place titanium solid electrode immersed into the 1moldm^-3 of acidified TiO2+ Connect this half cell with a salt bridge to the copper half cell and place the titanium half cell on the left Connect Electrodes with a high resistance voltmeter Stage 3: Record table of values of true emf of the cell Emf = ERHS - ELHS Emf = ECopper=ETitanium If average emf = 1.22v then this shows the E cell foe the titanium half cell is -0.88v
50
When creating a half cell: What conditions have to be met?
- electrode immersed in 1 MolDm^-3 of aqueous ion in solution - 298K
51
For copper to react it needs to be oxidised For this reaction to be feasible EReduced - EOxidised >0 most acids e cell = 0.00 , 0.00<0.34, ECell = -0.34 not feasible Nitric Acid e cell = 0.93, 0.93>0.34 , ECell = 0.62 Is feasible
52
Explain how you work out the overall equation of a Cell
Write half equations that is happening at the positive and negative electrodes make sure negative is in its oxidised form Equate the amount of electrons on either sides by multiplying Combine reactants and products either side of the —-> Cross out anything thats on both sides
53
What is the Function of the Porous Seperator
Allows ion movement between half cells Completes the circuit Acts as a salt Bridge
54
Explain why for a half cell connected to a lamp, does the potential difference eventually reach 0
The LHS gains positive charge as electrons are lost while the RHS looses positive charge as electrons are gained Eventually potential difference between the two half cells becomes 0, and the concentration of ions in both half cells are equal
55
The half equations for a glucose-oxygen cell at the negative and positive electrodes are given respectively. Give the conventional Representation of the Glucose Oxygen cell Negative extrude has a carbon electrode Positive electrode has a platinum Electrode

Chemistry (A2) (15 decks)

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