UAT-UK SPEC CODE: C12 (Electrolysis)ASSUMED MATHS 1 PREREQUISITE: M3.5FREQUENCY: VERY HIGH
Molten vs. Aqueous Electrolysis Discharge Competition & Electron Mole Stoichiometry
Deconstructed from 23 past UAT-UK questions (10.22% of all historical Chemistry papers). Students using standard A-Level classroom methods spend an average of 135s on this archetype—blowing past the 90s ESAT budget. Using the 2-line Sub-90 heuristic below compresses solve time to 35s (saving 100s per question).
Historical Frequency
23 Past Qs
10.22% of Chemistry
Classroom Trap Time
135s
+45s over 90s budget
Sub-90 Target Time
35s
Banks +100s on the clock
Dominant UI Format
Table Matching
Maths 1 Skill: M3.5
Card 1 & Card 2 Preview: The Classroom Time Trap vs. Sub-90 2-Line Rule
Excerpted from our interactive 6-Step Topic Lesson for ARCH-C-11.
CARD 1 OF 6 • THE CLASSROOM TIME TRAP (135s)
Why Students Bleed Time:
Compare molten vs. concentrated aqueous : in **molten **, the only ions present are and , so **sodium metal () forms at the cathode and chlorine gas () forms at the anode. In concentrated aqueous **, water provides and ions: at the cathode, since sodium is more reactive than hydrogen, **hydrogen gas ()** is discharged instead of ; at the anode, because the halide () is concentrated, **chlorine gas ()** is discharged (~110s).
In 23 past UAT-UK questions (10.22% of Chemistry), candidates lose 100s by in aqueous solution, metals above hydrogen in the reactivity series stay in solution while h+ is reduced to h2. Instead, apply C12 with Maths 1 skill M3.5.
CARD 2 OF 6 • THE 2-LINE SUB-90 HEURISTIC (<35s)
**Line 1 (Molten No Water):** Only (cathode) and (anode).
Line 2 (Conc. Aqueous): in reactivity at cathode; conc. halide at anode (20s).
Sanity & Limit Check: Verify units/signs against
multi_statement_linchpin_foil (Predicting sodium/magnesium metal at the cathode during electrolysis of AQUEOUS NaCl/MgSO4 (instead of H2 gas)) and multi_statement_linchpin_foil (Predicting SO4²- or NO3^- discharge at the anode instead of O2 gas from 4OH^- -> O2 + 2H2O + 4e^-).Examiner Distractor Blueprint for ARCH-C-11
FOIL #1multi_statement_linchpin_foil
Predicting sodium/magnesium metal at the cathode during electrolysis of AQUEOUS NaCl/MgSO4 (instead of H2 gas)
In aqueous solution, metals above hydrogen in the reactivity series stay in solution while H+ is reduced to H2.
FOIL #2multi_statement_linchpin_foil
Predicting SO4²- or NO3^- discharge at the anode instead of O2 gas from 4OH^- -> O2 + 2H2O + 4e^-
Sulfate and nitrate ions are never discharged in aqueous electrolysis; OH^- is oxidised to O2 unless a concentrated halide (Cl^-, Br^-, I^-) is present.
FOIL #3factor_of_two_or_stoichiometry_trap
Assuming equal moles of Al (Al³+ + 3e^-), Cu (Cu²+ + 2e^-), and Ag (Ag^+ + e^-) are deposited by the same charge Q
For fixed electron moles n(e^-), moles of metal deposited is n(e^-)/z (so Ag : Cu : Al = 1 : 1/2 : 1/3).
FOIL #4sign_or_direction_flip
Swapping cathode (reduction, negative in electrolysis) and anode (oxidation, positive in electrolysis) products
Reversing PANIC (Positive is Anode, Negative is Cathode) and OILRIG.
Try 1 Live Sample Question Under the 90-Second Stopwatch
Press W to open the 2-line dry-wipe scratchpad, select A–E, and lock in to reveal the Dual-View solution.
sub90 ESATARCH-C-11: Molten vs. Aqueous Electrolysis Discharge Competition & Electron Mole Stoichiometry (Sample)Chemistry
00:00.0
SUB-90 ZONE (<35S)
0.0s35s Sub-9090s ESAT Budget150s Classroom
Right-click any option to cross out • Keys
A–E + EnterQuestion 1 of 1 • 90s Target
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Chemistry•ARCH-C-11•Standard 5-Option
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