Electrode Potentials Theory

if you place two metals in a salt solution and connect them together, what happens?

electric current flows so that electrons pass from the more reactive metal to the less reactive.

why is a salt bridge used instead of a piece of wire in an electrical circuit

a wire only transfers electrons wheres a salt bridge transfers ions

what 2 metals form a Daniell cell?

zinc and copper

a stronger reducing agent will - electrons

lose electrons

porous pot can act as what

a salt bridge

what is used to compare the tendency of different metals to release electrons

the Standard Hydrogen Electrode

list all the components of the standard hydrogen electrode

platinum wire, hydrogen gas bubbled in (100kPa), finely divided platinum black, 1moldm^-3 HCl, salt bridge

explain the function of the salt bridge (2)

the ions in the ionic substance in the salt bridge move through the salt bridge to maintain charge balance

equation for hydrogen-oxygen fuel cell operating under alkaline conditions

O2 + 4H+ + 4e- → 2H2O

suggest the major advantage of using hydrogen as a fuel for cars via fuel cells instead of an internal combustion engine

internal combustion engine wastes a greater proportion of the available thermal energy

give the standard hydrogen electrode cell representation (as if it were in a full cell representation, use / as lines)

//H+(aq)/H2(g)/Pt(s)

why would the current fall to zero after the cell has operated for some time?

eventually the concentration of CuSO4 in each electrode will be the same

why would the electrons move from right to left?

the oncentration of Cu2+ ions is higher in the left half-cell. reaction of Cu2+ with 2e- will occur in preference at the left hand electrode.

give the half equations for the electrode reactions in an alkaline hydrogen-oxygen fuel cell:

H2 + 2OH- → 2H2O + 2e-. O2 + 4e- + 2H2O → 4OH-

how is an electric current generated in a hydrogen oxygen fuel cell

hydrogen electrode produces electrons. oxygen electrode accepts electrons.

why does a fuel cell not need to be recharged

there is a continuous supply of fuel

two major hazards associated with the use of a hydrogen-oxygen fuel cell in a vehicle

hydrogen is flammable, H+ is corrosive

why are rechargeable cells connected to solar cells which provide electrical energy for illuminated road signs?

solar cells do not supply energy all the time. rechargeable cells can store electrical energy for when the cells are not working.

give one reason why many waste disposal centres contain a separate section for cells and batteries

pollution of the environment by toxic substances

what electrode is used for the Fe3+ Fe2+ half cell

platinum

conditions for measuring emf

1kPa, 298K

deduce one essential property of the non-reactive porous separator labelled in the diagram

allows ions to pass through it

function of the carbon rod in this cell

inert electrode

why would a cell leak after being used for a long time

the metal container for the cell has reacted

why would the emf of a lead acid cell change after several hours

reagents are used up

why does the voltage remain constant in a fuel cell

the concentration of reagents remains constant

what flows in and out of a hydrogen oxygen fuel cell?

hydrogen and oxygen in, water out

what connects the two half cells in a hydrogen-oxygen fuel cell?

an electrolyte which carries charge

how does an electrolyte connect the half cells in an alkaline hydrogen oxygen fuel cell

facilitating the flow of OH- ions from the oxygen half cell to the hydrogen half cell

what is the only part of the fuel cell which remains in the fuel cell?

the electrolyte

what is the only part of the fuel cell which may need to be occassionally replaced?

the electrolyte

which is the negative terminal of the hydrogen oxygen fuel cell?

the hydrogen electrode

what reaction occurs in an alkaline hydrogen oxygen fuel cell at the negative electrode

2OH-(aq) + H2(g) → 2H2O(l) + 2e-

what is the positive terminal of an alkaline hydrogen-oxygen fuel cell?

the oxygen electrode

what reaction occurs in an alkaline hydrogen-oxygen fuel cell at the positive terminal?

1/2O2(g) + H2O(l) +2e- → 2OH-(aq)

what is the full equation for the hydrogen oxygen fuel cell?

1/2O2(g) + H2(g) → H2O(l)

how does an electrolyte connect the half cells in an alkaline hydrogen oxygen fuel cell

facilitates the flow of H+ ion from the hydrogen half cell to the oxygen half cell

what reaction occurs in the hydrogen half cell of an acidic hydrogen-oxygen fuel cell

H2(g) → 2H+(aq) + 2e-

what reaction occurs in the oxygen half cell of an acidic hydrogen-oxygen fuel cell

1/2O2(g) + 2H+(aq) + 2e- → H2O(l)

what is the overall reation for the acidic hydrogen oxygen fuel cell

1/2O2(g) +H2(g) → H2O(l)

why might hydrogen-oxygen fuel cells NOT be regarded as a carbon neutral source of energy

H2 may be made using an energy source that is not carbon neutral

when the standard electrode potential for Fe3+/Fe2+ is measured, a platinum electrode is requried. what is the function of the platinum electrode.

provide a reaction surface

SHE always goes on the

left

the electrode with the more negative E standard value always goes on

the left

reduction occurs at which electrode?

positive

oxidation occurs at which electrode

negative

for the Fe2+/Fe3+ electrode, what 2 key elements are needed

platinum electrode, mixture of soluble Fe2+ and Fe3+ compounds both at 1 moldm^-3

3 marks for measuring change in mass of an electrode

allow cell to discharge until [reagent] has halved. use an experiment to determine [reagent], i.e. colorimetry. measure electrode mass before and after.

why may the recharging of the lithium cell produce CO2

energy needed to recharge may come from the combustion of carbon containing compound like fossil fuels

why would K2CO3 not be used for a salt bridge when the SHE is used

the carbonate ions react with the acid present

the reaction which occurs at the positive electrode of the lithium cell

Li^+ + CoO2 + e^- → Li^+[CoO2]^-

the reaction which occurs at the negative electrode of the lithium cell

Li → Li^+ + e^-