75-Archetype SyllabusChemistry • ARCH-C-04 • Spec C4

Full 6-Card Lesson 15-Question Timed Drill

UAT-UK SPEC CODE: C4 (Quantitative chemistry)ASSUMED MATHS 1 PREREQUISITE: M1.2FREQUENCY: VERY HIGH

Molar Gas Volume (24 dm^3 at rtp), Ideal Gas Scaling, Percentage Yield & Atom Economy

Deconstructed from 18 past UAT-UK questions (8% of all historical Chemistry papers). Students using standard A-Level classroom methods spend an average of 150s on this archetype—blowing past the 90s ESAT budget. Using the 2-line Sub-90 heuristic below compresses solve time to 40s (saving 110s per question).

Historical Frequency

18 Past Qs

8% of Chemistry

Classroom Trap Time

150s

+60s over 90s budget

Sub-90 Target Time

40s

Banks +110s on the clock

Dominant UI Format

5-Option A–E

Maths 1 Skill: M1.2

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-04.

Launch All 6 Active-Recall Cards

CARD 1 OF 6 • THE CLASSROOM TIME TRAP (150s)

Why Students Bleed Time:

First calculate the moles of magnesium:

n(\text{Mg}) = \frac{0.60}{24} = 0.025\text{ mol}

. From the

1:1

stoichiometry,

n(\text{H}_2) = 0.025\text{ mol}

. At rtp,

V(\text{H}_2) = 0.025 \times 24\text{ dm}^3 = 0.60\text{ dm}^3 = 600\text{ cm}^3

(~105s).

In 18 past UAT-UK questions (8% of Chemistry), candidates lose 110s by mixing cm³ and dm³ without applying 1 dm³ = 1000 cm³. Instead, apply C4 with Maths 1 skill M1.2.

CARD 2 OF 6 • THE 2-LINE SUB-90 HEURISTIC (<40s)

**Line 1 (

24

Cancellation):**

V(\text{cm}^3) = \frac{m}{A_r} \times 24,000 = \frac{0.60}{24} \times 24,000

**Line 2 (Cancel

24

):**

0.60 \times 1000 = 600\text{ cm}^3

(20s).

Sanity & Limit Check: Verify units/signs against unit_or_prefix_mismatch (Dividing cm³ by 24 instead of 24,000 when converting gas volume at rtp to moles) and factor_of_two_or_stoichiometry_trap (Using atomic mass instead of diatomic M_r (e.g. 14 instead of 28 for N₂, or 35.5 instead of 71 for Cl_2) when converting gas volume to mass).

Examiner Distractor Blueprint for ARCH-C-04

FOIL #1unit_or_prefix_mismatch

Dividing cm³ by 24 instead of 24,000 when converting gas volume at rtp to moles

Mixing cm³ and dm³ without applying 1 dm³ = 1000 cm³.

Open Unit / Prefix Mismatch Clinic

FOIL #2factor_of_two_or_stoichiometry_trap

Using atomic mass instead of diatomic M_r (e.g. 14 instead of 28 for N₂, or 35.5 instead of 71 for Cl_2) when converting gas volume to mass

Forgetting that common elemental gases (H2, N2, O2, F2, Cl2) are diatomic.

Open Factor-of-2 / Stoichiometry Clinic

FOIL #3subsystem_isolation_trap

Swapping percentage yield (actual / theoretical * 100%) with atom economy (M_r of desired product / sum of M_r of all products * 100%)

Confusing experimental reaction efficiency (% yield) with stoichiometric formula utilization (atom economy).

Open Subsystem Isolation Trap Clinic

FOIL #4intermediate_stop_trap

Calculating theoretical 100% gas volume without multiplying by the given percentage yield fraction

Stopping at theoretical stoichiometric yield before scaling by actual % yield.

Open Intermediate Stop 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-04)

ARCH-C-04: Molar Gas Volume (24 dm^3 at rtp), Ideal Gas Scaling, Percentage Yield & Atom Economy (Sample)Chemistry

00:00.0

SUB-90 ZONE (<40S)

0.0s40s Sub-9090s ESAT Budget150s Classroom

Question 1 of 1ARCH-C-04 (6-Card Lesson)Format: Standard 5-Option

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

Question 1 of 1 • 90s Target

Ready to Start Question 1?

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-04•Standard 5-Option

or press Enter to start