Topic 14 Flashcards
How do you setup an electrochemical cell?
- OBtain metals and clean to remove impurities
- Wash metals with propanone and place into solutions with the same ion
- Make a salt bridge with filterpaper soaked in saturated KNO2 or KCl linking the two beakers
- Connect the electrodes to a voltmeter and power source
What is redox?
- Reduction = Gain of electrons
- Oxidation = Loss of electrons
OIL RIG
What are reducing agents?
- They are oxsidised themselves
- Loose electrons
- Helps reduce another atom
What is a oxsidising agent?
- Reduces itself
- Gains electrons
- Helps oxsisdise other substances
What are half cells?
- One half of a chemical cell
- Constructed of a metal dipped in its ion
- OR a platinum electrode with 2 aqueous ions
What reactions occur in an ion half cell?
Fe2+ + 2e- <-> Fe
Why do we use a platinum electrode?
- Its inert but electrically conductive
- It allows for electricity to travel up electrode and into next cell
What happens in an electrochemical cell?
- One side undergoes reduction the other oxidation
- Redox reaction
- Voltmeter find the Ecell / EMFwhich is the pd between the two
- Elecrons flow from a less reactive metal to the more reactive cell
What is the standard electrode potential?
- Voltage produced from a standard half cell connected to a hydrogen half cell
- Standard hydrogen half cell = 0V
- Needed to compare other half cells
- Under standard conditions
- 298K
- 100 kPa
- 1 mol dm-3 conc of ions
What does the standard hydrogen potential look like?
How do you work out EMF?
- Use the electrode potentials of each half cell
- EMF = Reduced - Oxidised
- Larger V = Reduced
What is the setup for a non metal and metal half cell
What happens when a copper half cell and a hydrogen half cell is turned on
What is cell notation?
How can you predict feasibility using standard electrode potential?
- Work out standard EMF
- Reduced - Oxidised
- If the value is positive it is reduced
- The reaction is feasible
What is the E cell directionally proportional to?
- Proportional to the total entropy
- And to lnK for a reaction
What effects the standard electrode potential
- Different conditions effect the position of equilibrium
- IF equilibrium changes, cell potential value changes too
- Standard conditions are used allowing for comparisons
Why may a reaction that is calculated to be feasible not occur?
- reactants are KINETICALLY STABLE which means that the reaction would have a high activation energy -> rate of reaction would be too slow
- non standard conditions
What is a electrochemical series?
- A list of electrode potentials
- Allowing for you to find them in the data booklet
- Calculate EMF (Reduced - Oxidised)
How can you work out the feasibility of a disproportionation reaction using standard electrode potential?
- Identify which half equation has been oxidised (more negative)
- Reverse equation and combine half equations to obtain a feasible reaction
- Calculate E cell to calculate feasibility
What are the half equations in the Lithium ion cell?
What is the setup for a hydrogen fuel cell?
What are the steps in hydrogen fuel cells?
- Hydrogen is fed into the left side
- Reacts with OH- (2H + 4OH → 4H2O +4e-)
- Electrons produced travel through platinum electrode
- Intert but conductive
- Flow of electrons power somthinG
- Oxygen fed into cell
- Reacts with water + e- made from step 1
- O2 + 2H2O +4e- → 4OH
- Cathode (-) e- flow to electrode
- Electrolytes (KOH) carries OH- ions made to anode
- E- flow from anode (+)
- Water is eliminated and released into surroundings
- OH- ions from step 4 carried to anode via eletctrode
What are alcohol fuel cells
###
- Uses for methanol and ethanol
- Reforms them to use hydrogen
- Alcohol is oxidised at the anode with water present
- CH2OH + H20 → CO2 + 6e- + 6H+
- H+ ions then pass through electrode
- 6H+ + 6e- + 1.52 → 3H2O
