Chemistry: Electrochemistry

in terms of redox, what happens when a soluble gold(I) compound containing Au+ ions is added to water. State what you would observe. Write an equation for the reaction that occurs.:

Au+ + e- -> Au = 1.68V

O2 + 4H+ +4e- ->2H2O = 1.23V

in terms of redox, what happens when a soluble gold(I) compound containing Au+ ions is added to water. State what you would observe. Write an equation for the reaction that occurs.

Gold metal / solid / precipitate OR bubbles / effervescence of (oxygen gas) / gas produced

2Au+ + H2O → 2Au + 2H+ + 1/2O2

What's the purpose of the salt bridge and what's a requirement of the salt bridge

Purpose: Allow movement of ions between electrodes

Requirement: Must not react with the electrolyte / ions in solution

A salt bridge was used in a cell to measure electrode potential. Explain the function of the salt bridge.

The ions in the ionic substance in the salt bridge move through the salt bridge 1 To maintain charge balance / complete the circuit

There are two ways to use hydrogen as a fuel for cars. One way is in a fuel cell to power an electric motor, the other is as a fuel in an internal combustion engine. Suggest the major advantage of using the fuel cel

A fuel cell converts more of the available energy from combustion of hydrogen into kinetic energy of the car / an internal combustion engine wastes more (heat) energy

Draw a labelled diagram of a suitable apparatus for the right-hand electrode in this cell. You do not need to include the salt bridge or the external electrical circuit.

Draw a labelled diagram of a suitable apparatus for the right-hand electrode in this cell. You do not need to include the salt bridge or the external electrical circuit.

The Pt electrode must clearly be in contact with a solution of a named acid.

Suggest why the recharging of a lithium cell may lead to release of carbon dioxide into the atmosphere.

Electricity for recharging the cell may come from power stations burning (fossil) fuel

Hydrogen-oxygen fuel cells are used to provide electrical energy for electric motors in vehicles. (a) In a hydrogen-oxygen fuel cell, a current is generated that can be used to drive an electric motor. (i) Deduce half-equations for the electrode reactions in a hydrogen-oxygen fuel cell.

ii)Use these half-equations to explain how an electric current can be generated.

iii)Explain why a fuel cell does not need to be recharged.

b) Identify one major hazard associated with the use of a hydrogen-oxygen fuel cell in a vehicle.

a) i) H2 + 2OH- → 2H2O + 2e- / H2 → 2H+ + 2e

O2 + 4e- + 2H2O → 4OH- / O2 + 4H+ + 4e- → 2H2O

ii) Hydrogen (electrode) produces electrons

Oxygen (electrode) accepts electrons

iii)Hydrogen / the fuel / reactants supplied continuously / fed in

b)Hydrogen is flammable / H+ corrosive / OH- corrosive / hydrogen explosive

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

Prevent pollution of the environment by toxic or dangerous substances / recycling of valuable components

What is the function of the platinum electrode?

to allow transfer of electrons / provide a reaction surface

NO3-+4H+ + 3e- -> NO+2H2O = 0.96V

Cu2+ + 2e- -> Cu = 0.34V

2H+ + 2e- ->H2

Use the given data to explain why copper reacts with dilute nitric acid but has no reaction with dilute HCl

emf for cell must be positive for the reaction to occur/be spontaneous

Cu+2H+ -> products, has an emf of -0.34V, therefore won't happen

the Cu electrode is more positive than the hydrogen electrode, so it wont work

name the standard reference electrode against which electrode potentials are measured, and state the conditions

hydrogen eelctrode, 1M HCl, 298K, hydrogen gas at 100kPa, no current flowing

S2O82- + 2e- -> 2SO4- E=2.01V

Ag+ + e- -> Ag E= 0.80V

A cell is produced when these two half-cells are connected. Deduce the cell potential and write the equation for the spontaneous reaction. State how the electrode potential of the S2O82-/SO42- equilibrium would change if the concentration of SO42- ions was increased. Explain

1.21V,

S2O82-+ 2Ag -> 2SO42- + 2Ag+

the potential decreases as the equilibrium is displaced to the left, so more electrons are released.

what's the job of the standard hydrogen electron

reference electrode

give one reason why the emf of a cell changes when the electrodes are connected and a current flows

the concentration of the ions are no longer standard.

electrode potentials are usually measured by reference to a secondary standard electrode. Identify a secondary standard electrode and give a reason why it is used rather than a standard hydrogen electrode

AgCl, it's easier to use