3.1 Standard Electrode Potentials Flashcards
Define oxidation number
The number of electrons an atom uses to bond with atoms of another element
How do electrochemical cells work?
- use redox reaction as the transfer of electrons creates a flow of electrons
- flow of charged particles is an electrical current which flows between electrodes in the cell
- potential difference created between 2 electrodes which can be measured
What is the purpose of a salt bridge in electrochemical cells?
- tube of unreactive ions that move between the solutions to carry the flow of charge but will not interfere with reaction
—> ie KNO3 or KCl
Draw an electrochemical cell
Draw the standard hydrogen electrode
Define standard electrode potential
Electromotive force (EMF) of a cell impaired with a standard hydrogen half cell measured at 298K with a solution concentration 1moldm3 and a gas pressure of 100kPa
How do you calculate the overall Eθ
Most positive - most negative
What do more positive and more negative potentials mean?
Positive: substances are more easily reduced and will gain electrons therefore oxidising agent
Negative: substances are more easily oxidised and will lose electrons therefore reducing agent
Why are platinum electrodes used in the SHE?
- metallic so conduct electricity
- inert so don’t interfere
What does a positive overall cell potential mean?
- reaction is spontaneous and favourable
Describe fuel cells including pros and cons
- generate electrical gradient without needing to be recharged
- usually hydrogen fuel cell - use continuous supply of hydrogen and oxygen from the air to generate a continuous current
PROS:
- only waste product is water so seen as environmentally friendly
CONS:
- energy required to produce a supply of hydrogen and oxygen
- hydrogen highly flammable so required careful storage and transportation
Steps to. Instructing redox half equations
- balance
- balance charges with e-
- balance O with water
- balance H with H+
What does a more positive Eθ mean?
Stronger oxidising agent
Half equations at electrodes and overall equation for a hydrogen fuel cell
Anode: H2 —> 2H + 2e-
Cathode: O2 + 4H+ + 4e- —> 2H2O
Overall: 2H2 + O2 —> 2H2O
State one use for sodium chlorate
Bleach to kill bacteria
What does electrode potential of a half cell indicate?
Its tendency to lose or gain electrons
What do positive/negative voltmeter values mean for direction of current?
positive: left to right
negative: right to left
State the effect an alkaline solution will have on the value of the electrode potential of the oxygen half cell
- electrode potential will be more negative
- alkaline solution reduce conc of H+ so equilibrium will move left
