75-Archetype SyllabusChemistry • ARCH-C-05 • Spec C5

Full 6-Card Lesson 15-Question Timed Drill

UAT-UK SPEC CODE: C5 (Oxidation, reduction and redox)ASSUMED MATHS 1 PREREQUISITE: M4.2FREQUENCY: HIGH

Oxidation State Assignment, Redox Disproportionation & Ionic Half-Equation Balancing

Deconstructed from 13 past UAT-UK questions (5.78% of all historical Chemistry papers). Students using standard A-Level classroom methods spend an average of 130s on this archetype—blowing past the 90s ESAT budget. Using the 2-line Sub-90 heuristic below compresses solve time to 35s (saving 95s per question).

Historical Frequency

13 Past Qs

5.78% of Chemistry

Classroom Trap Time

130s

+40s over 90s budget

Sub-90 Target Time

35s

Banks +95s on the clock

Dominant UI Format

1-2-3 Statement

Maths 1 Skill: M4.2

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-05.

Launch All 6 Active-Recall Cards

CARD 1 OF 6 • THE CLASSROOM TIME TRAP (130s)

Why Students Bleed Time:

Evaluate each statement: (1) In elemental

\text{Cl}_2

\text{Cl}

has oxidation state

0

; in

\text{NaCl}

it is

-1

; in

\text{NaClO}

(+1) + x + (-2) = 0 \implies x = +1

(Statement 1 is correct). (2) Because chlorine is simultaneously oxidised (

0 \rightarrow +1

) and reduced (

0 \rightarrow -1

), it undergoes disproportionation (Statement 2 is correct). (3) Oxygen has oxidation state

-2

in all species here; only in peroxides (

\text{O}_2^{2-}

) is it

-1

(Statement 3 is incorrect) (~120s).

In 13 past UAT-UK questions (5.78% of Chemistry), candidates lose 95s by confusing 'is oxidised' (loses electrons = reducing agent) with 'oxidising agent' (gains electrons = is reduced). Instead, apply C5 with Maths 1 skill M4.2.

CARD 2 OF 6 • THE 2-LINE SUB-90 HEURISTIC (<35s)

Line 1 (Kill Statement 3): Oxygen is

-2

\text{NaClO}

(not a peroxide)

\implies

Statement 3 False.

Line 2 (Verify 1 & 2):

\text{Cl}: 0 \rightarrow -1

and

+1

(disproportionation)

\implies

1 and 2 only (25s).

Sanity & Limit Check: Verify units/signs against sign_or_direction_flip (Identifying the species that is oxidised as the oxidising agent (instead of the reducing agent)) and factor_of_two_or_stoichiometry_trap (Forgetting to divide by subscript 2 in Cr_2O_7²- (giving +12 instead of +6 for Cr) or S_2O_3²-).

Examiner Distractor Blueprint for ARCH-C-05

FOIL #1sign_or_direction_flip

Identifying the species that is oxidised as the oxidising agent (instead of the reducing agent)

Confusing 'is oxidised' (loses electrons = reducing agent) with 'oxidising agent' (gains electrons = is reduced).

Open Sign / Direction Flip Clinic

FOIL #2factor_of_two_or_stoichiometry_trap

Forgetting to divide by subscript 2 in Cr_2O_7²- (giving +12 instead of +6 for Cr) or S_2O_3²-

Computing total oxidation state of 2 atoms without dividing by 2.

Open Factor-of-2 / Stoichiometry Clinic

FOIL #3multi_statement_linchpin_foil

Classifying a reaction where two different reactants form one product (comproportionation) or normal redox as disproportionation

Disproportionation requires ONE element in a SINGLE reactant species to be simultaneously oxidised and reduced (e.g. Cl_2 -> Cl^- + ClO_3^-).

Open Multi-Statement Linchpin Foil Clinic

FOIL #4fence_post_or_domain_trap

Assigning oxygen as -2 in H_2O_2 (peroxide, -1) or OF_2 (+2), or hydrogen as +1 in metal hydrides NaH (-1)

Missing the peroxide (-1), oxygen difluoride (+2), and metal hydride (-1) oxidation state exceptions.

Open Fence-Post / Domain Trap Clinic

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.

Full 6-Card Lesson Launch All 15 Questions (ARCH-C-05)

ARCH-C-05: Oxidation State Assignment, Redox Disproportionation & Ionic Half-Equation Balancing (Sample)Chemistry

00:00.0

SUB-90 ZONE (<35S)

0.0s35s Sub-9090s ESAT Budget150s Classroom

Question 1 of 1ARCH-C-05 (6-Card Lesson)Format: Standard 5-Option

Right-click any option to cross out • Keys A–E + Enter

Question 1 of 1 • 90s Target

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The question stem, diagram, and answer options are hidden behind this pre-start gate. When you click below, the question will reveal and your 90-second split stopwatch will immediately begin ticking.

Chemistry•ARCH-C-05•Standard 5-Option

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