3.1.11 Electrode

When we place a rod of a metal in a solution of its salt/ions. Forming an equilibrium.
Eg placing a zinc rod in a Zn(NO3)2 aq solution
Always do NO3 salts(easiest)

Oxidation and reduction occurs
Zn(s) ----> Zn$^{2+}$ + 2e$^{-}$
Zn$^{2+}$ + 2e$^{-}$ ----> Zn(s)
This creates a potential difference as electrons goes to electrode

Zn +2e$^{-}$ ⇌ Zn
Always do reduction reaction as its IUPAC way

The more reactive, the more negative its electrode value
The less the reactive, the more POSITIVE its electrode potential value
NO PRoblem

Shows the redox reaction but shorter
eg:
Zn$^{2+}$ +2e$^{-}$ ⇌ Zn
becomes
Zn$^{2+}$/Zn

Filter paper/wire that completes the circuit and is soaked in an inert salt (eg KNO3)
Allows its ions to flow into electrolytes to neutralise excess charge being build up

More reactive metal OXIDISES and less reactive reduces.
Zn--> Zn$^{2+}$ + 2e-
Cu + 2e$^-$ --> Cu$^{2-}$

Bubble it through a tube and use platinum electrode

Its a standard hydrogen electrode which is used as a reference.
Its electrode potential is 0

The measured voltage when 2 electrodes connected
If youre using SHE that emf value = electron potential of the other cell AND If that other half cell is standard its symbol is E$\theta$

Uses high resistance voltmeter
Platinum electrode
298K
100kPa hydrogen gas
1mol/dm$^3$ HCL as H+ source( if diprotic 0.5 as we actually want 1 mol of H+)

Reduction electrode potential - oxidation electrode potential
Order is same as like RED OX

Zn(s)|Zn$^{2+}$(aq) | | Cu$^{2+}$(aq)|Cu(s)
Oxidation is on left(unless theres a SHE in which SHE will be on left) and flip its redox reaction so its actually a oxidation reaction
Write it in order they appear in half equation
use phase boundary "|" when they change state
Add salt bridge symbol "| |" when you finish left side

Pt|Fe$^{2+}$(aq) Fe$^{3+}$ | |Cl2(g)|2Cl${^-}$(aq)|Pt
Dont add phase boundary if same state and instead use comma
Add Pt at the beginning or end if used

Uses:smoke detectors, clocks,toys
Doesnt generate large currents so used in low power devices
Single use BUT long lasting
Uses a irreversible reaction
Discharging only
Has less toxic chemicals

Uses: Laptop,phone,cameras
Generates large currents so used in high power devices
Multi-use but shorter life per charge
Reversible reaction
Discharges then RECHARGES(lifetime becomes shorter per charge)
Has more toxic chemicals

Via contiguous supply of chemicals
Skipped some numbers
1)Hydrogen fed here and reacts with OH- to form 4H2O and 4 e
2)Electrons travel through platinum anode electrode
3)Flow of electrons used to power smth like car
4) Oxygen fed here and reacts with water and the 4e forming 4OH-
6)electrolyte(salt bridge) made of KOH carries OH- down back to anode/left side
8)Product from step 1 (H20) released

- Ion exchange membranes (borders of electrolye) allow OH- to pass thru but NOT hydrogen or oxygen

Fuel cell only waste product is H2O
More efficient and generates more useful energy than heat

Hydrogen is HIGHLY flammable so storage and transport is expensive and complex
Hydrogen needed is produced via fossil fuel combustions