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UAT-UK SPEC: C5MODULE: CHEMISTRYTOPIC ID: ARCH-C-05

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

Master Oxidation State Assignment, Redox Disproportionation & Ionic Half-Equation Balancing on the ESAT Chemistry paper. Traditional classroom derivations waste valuable seconds. Using the 2-step Sub-90 invariant elimination method compresses solve time to 35s, saving +95s per question.

Standard Classroom Time
130s
Textbook multi-line derivations bleed exam clock
Sub-90 Target Pace
35s
Comfortably below the 88.8s per-question limit
Time Saved for Review
+95s
Banks clock buffer across 27 questions

2-Step Sub-90 Shortcut Formula

How to eliminate intermediate algebra and solve under 45 seconds.

Launch Interactive Lesson
STEP 1 • SETUP INVARIANT (LINE 1)10–15s
Line 1 (Kill Statement 3): Oxygen is −2-2 in NaClO\text{NaClO} (not a peroxide)   ⟹  \implies Statement 3 False.

Establish the structural invariant and eliminate impossible options immediately.

STEP 2 • FAST SOLVE (LINE 2)15–25s
Line 2 (Verify 1 & 2): Cl:0→−1\text{Cl}: 0 \rightarrow -1 and +1+1 (disproportionation)   ⟹  \implies 1 and 2 only (25s).

Evaluate the simplified expression using integer factoring or unit elimination.

Distractor Trap Forensics

The predictable cognitive traps engineered by examiners into the wrong options.

TRAP #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).

Sub-90 Fix: Test invariants before expanding equations.
TRAP #2factor_of_two_or_stoichiometry_trap

Forgetting to divide by subscript 2 in Cr(2O, 7)²⁻ (giving +12 instead of +6 for Cr) or S(2O, 3)²⁻

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

Sub-90 Fix: Test invariants before expanding equations.
TRAP #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. Cl₂ -> Cl⁻ + ClO₃⁻).

Sub-90 Fix: Test invariants before expanding equations.

Try 1 Timed Question: Oxidation State Assignment, Redox Disproportionation & Ionic Half-Equation Balancing

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Full Lesson All 15 Questions (ARCH-C-05)
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ARCH-C-05: Oxidation State Assignment, Redox Disproportionation & Ionic Half-Equation Balancing (Sample)Chemistry
00:00.0
SUB-90 ZONE (<50S)
0.0s50s Sub-9090s ESAT Budget150s Classroom
Question 1 of 1ARCH-C-05 (6-Card Lesson)Format: 1-2-3 Multi-Statement Combination
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Question 1 of 1 • 90s Target

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Chemistry•ARCH-C-05•1-2-3 Multi-Statement
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