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A2 Chemistry > EMF > Flashcards

EMF Flashcards

1
Q

what is electrode potential a measure of?

A

oxidising ability

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2
Q

what does a high and positive electrode potential mean?

A

very good oxidising agent

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3
Q

what is the emf of a standard hydrogen electrode?

A

0

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4
Q

why is the emf of the she 0?

A

acts as a baseline - used as a comparison

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5
Q

how should the standard hydrogen electrode and the other half cell be connected?

A

with a high resistance voltmeter and a salt bridge

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6
Q

how can you make a salt bridge?

A

soak filter paper in potassium chloride/nitrate

fill a u tube with KCl in agar jelly

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7
Q

what is the purpose of a salt bridge?

A

completes the circuit

balances the charges

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8
Q

why do you stopper the end of a salt bridge with cotton wool?

A

to stop too much mixing of salt bridge solution with the contents of the two beakers

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9
Q

describe how the standard hydrogen electrode is set up

A

solution of H+ ions
platinum electrode (platinum foil over porous platinum)
H2 gas

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10
Q

what standard conditions are all half cells under?

A

all solutions are 1M
gases at 100kPa
298K temp

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11
Q

why do half cells need to be under standard conditions?

A

because the equilibrium shifts with a change in conditions

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12
Q

why is a high resistance voltmeter needed when connecting two half cells?

A

to avoid the flow of current because this will cause a drop in the voltage

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13
Q

define standard electrode potential

A

the electrode potential of a standard electrode with ion conc of 1M at 298K connected to a standard H electrode using a high resistance voltmeter and salt bridge

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14
Q

which side does the oxidation half cell go on?

A

the left

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15
Q

which side does the reduction electrode go on?

A

the right

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16
Q

what is the equation to find the EMF of a whole cell?

A

E(rhs)-E(lhs)

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17
Q

explain how electrode potentials can show the feasability of a cell?

A

the more positive a cell’s emf, the more feasible the reaction

18
Q

which side is the SHE always on?

A

the left

19
Q

give a commercial use of cells

A

commercial source of electrical energy

20
Q

what are primary cells?

A

single use/disposable cells

21
Q

what are secondary cells?

A

rechargeable cells

22
Q

what’s an example of a non-rechargeable cell?

A

Zn and MnO2

23
Q

advantages of non-rechargeable cells

A

low cost

non-toxic material

24
Q

disadvantages of non-rechargeable cells

A

can leak
cannot be recycled
unstable

25
Q

give examples of rechargeable cells

A

nickel cadmium
lead-acid
lithium ion

26
Q

give some uses of lithium ion cells

A

provide electrical energy for tablets, laptops and phones

27
Q

what is the purpose of graphite powder in a lithium fuel cell?

A

acts as a support medium

28
Q

why can water not be used in a lithium fuel cell?

A

reacts with the lithium

29
Q

give the equation of the oxidation reaction in a lithium ion cell

A

Li —-> Li+ + e-

30
Q

give the equation of the reduction reaction in a lithium ion cel

A

e- + Li+ + CoO2 —> Li+[CoO2]-

31
Q

give the cell notation for a lithium ion cell

A

Li(s)/Li+(aq) // Li+, CoO2/ Li+[CoO2]-

32
Q

advantages of rechargeable cells?

A

reusable
prevents waste
slows depletion of metals and other reagents
less energy used to extract metals

33
Q

what is a fuel cell?

A

a cell which converts chemical energy from a redox reaction into electrical energy (generate an electric current)

34
Q

what are the main types of fuel cell?

A

hydrogen or ethanol

35
Q

give the oxidation reaction in an acidic hydrogen fuel cell

A

H2(g) —-> 2H+(aq) + 2e-

36
Q

give the reduction reaction in the acidic hydrogen fuel cell?

A

O2(g) + 4H+ + 4e- —–> 2H2O (l)

37
Q

give the oxidation reaction in an alkaline hydrogen fuel cell

A

H2 + 2OH- —-> 2H2O

38
Q

give the reduction reaction in an alkaline hydrogen fuel cell

A

O2 (g) + 2H2O + 4e- —-> 4OH-

39
Q

what are the advantages of fuel cells?

A

no need to recharge them
run for as long as you supply them with fuel
steady output of voltage
doesn’t generate CO2 - only product is water

40
Q

what is the advantage of using fuel cells in cars?

A

uses more available energy for kinetic energy so less energy is wasted as heat

41
Q

what are the disadvantages of fuel cells?

A

not carbon neutral bc CO2 released when the methane and steam react to form hydrogen
expensive
difficult to store
flammable

A2 Chemistry (17 decks)

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