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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)

A
25
Q

What reactions occur in Nickel/Cadmium Cell Electrodes (AA Batteries)

A

(1st one is at net electrode)

26
Q

What reactions occur on discharge in Lithium Ion Cells

A
27
Q

What is a Fuel Cell?

A

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
Q

What are the Reactions that take place at the two electrodes in an alkaline fuel cell

A
29
Q

Draw a diagram of a hydrogen fuel cell

A
30
Q

Why is it better to use a fuel cell then to burn H2 in air

Even if the same reaction occurs

A

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
Q

What are the Disadvantages to hydrogen fuel Cells

A

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
Q

What are the Advantages to Fuel cells

A

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
Q

How do you find the weakest reducing agent

A

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
Q

How do you find the Weakest Oxidising agent

A

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
Q

How do you find the most powerful oxidising agent

A

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
Q

How do you find the most powerful reducing agent

A

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
Q

What is the reason some cells cannot be reachrged

A

The reaction of the cell isn’t reversible, products cannot be converted back into reactants

38
Q

How can the emf of a cell be kept constant

A

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
Q

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

A

0.56 (Right) — -3.04(Left) = 3.60v

40
Q

What reactions occur at a acidic hydrogen oxygen fuel cell?

A
41
Q

What is the emf of an acidic and alkaline hydrogen oxygen fuel cell

A

1.23v

42
Q

What does Acidify mean

A

Reduced, gained electrons

43
Q
A

A List of electrode Potentials (E Cell) in Numerical Order

44
Q

From the Table Below

Write an Equation for the reaction between VO2 + and iron to form VO (2+)

A
45
Q
A

Non Standard Conditions

46
Q
A
47
Q

How do you maintain a Constant Emf in a Fuel Cell

A

Reactants must be constantly supplied at the same rate

48
Q
A
49
Q
A

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
Q

When creating a half cell: What conditions have to be met?

A
  • electrode immersed in 1 MolDm^-3 of aqueous ion in solution
  • 298K
51
Q
A

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
Q

Explain how you work out the overall equation of a Cell

A

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
Q

What is the Function of the Porous Seperator

A

Allows ion movement between half cells

Completes the circuit

Acts as a salt Bridge

54
Q

Explain why for a half cell connected to a lamp, does the potential difference eventually reach 0

A

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
Q

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

A

Chemistry (A2) (15 decks)

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