75-Archetype SyllabusChemistry • ARCH-C-07 • Spec C8

Full 6-Card Lesson 15-Question Timed Drill

UAT-UK SPEC CODE: C8 (Separation techniques)ASSUMED MATHS 1 PREREQUISITE: M3.5FREQUENCY: MEDIUM

Solubility Curves (g per 100 g Water), Recrystallisation Mass & Paper/TLC Chromatography R_f

Deconstructed from 10 past UAT-UK questions (4.44% of all historical Chemistry papers). Students using standard A-Level classroom methods spend an average of 145s on this archetype—blowing past the 90s ESAT budget. Using the 2-line Sub-90 heuristic below compresses solve time to 40s (saving 105s per question).

Historical Frequency

10 Past Qs

4.44% of Chemistry

Classroom Trap Time

145s

+55s over 90s budget

Sub-90 Target Time

40s

Banks +105s on the clock

Dominant UI Format

5-Option A–E

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-07.

Launch All 6 Active-Recall Cards

CARD 1 OF 6 • THE CLASSROOM TIME TRAP (145s)

Why Students Bleed Time:

Per

100\text{ g}

of water, cooling from

60\,^\circ\text{C}

20\,^\circ\text{C}

precipitates

110 - 30 = 80\text{ g}

\text{KNO}_3

. Scaling to

50\text{ g}

of water gives

\frac{50}{100} \times 80 = 40\text{ g}

(~100s).

In 10 past UAT-UK questions (4.44% of Chemistry), candidates lose 105s by if solubility at t_hot is 80 g / 100 g water, 100 g of saturated *solution* contains 100*(100/180) g of water, not 100 g of water! Instead, apply C8 with Maths 1 skill M3.5.

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

**Line 1 (

\Delta S

per

100\text{ g}

):**

\Delta S = 110 - 30 = 80\text{ g}

**Line 2 (Scale to

50\text{ g}

Water):**

\frac{50}{100} \times 80 = 40\text{ g}

(20s).

Sanity & Limit Check: Verify units/signs against subsystem_isolation_trap (Scaling solubility difference (S_hot - S_cold) by total saturated SOLUTION mass instead of pure WATER solvent mass) and intermediate_stop_trap (Outputting the mass remaining dissolved at T_cold instead of the mass of crystals precipitated (m_hot - m_cold)).

Examiner Distractor Blueprint for ARCH-C-07

FOIL #1subsystem_isolation_trap

Scaling solubility difference (S_hot - S_cold) by total saturated SOLUTION mass instead of pure WATER solvent mass

If solubility at T_hot is 80 g / 100 g water, 100 g of saturated *solution* contains 100*(100/180) g of water, not 100 g of water!

Open Subsystem Isolation Trap Clinic

FOIL #2intermediate_stop_trap

Outputting the mass remaining dissolved at T_cold instead of the mass of crystals precipitated (m_hot - m_cold)

Stopping at final dissolved mass without subtracting from initial dissolved mass.

Open Intermediate Stop Trap Clinic

FOIL #3fence_post_or_domain_trap

Measuring R_f distance from the bottom edge of the chromatography paper instead of the pencil baseline origin

Failing to subtract the baseline offset from spot and solvent front heights.

Open Fence-Post / Domain Trap Clinic

FOIL #4factor_of_two_or_stoichiometry_trap

Forgetting to scale by (V_water / 100) when water volume is 50 cm³ or 250 cm³ instead of 100 cm³

Reading raw y-axis values (per 100 g water) without scaling to the actual water mass.

Open Factor-of-2 / Stoichiometry 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-07)

ARCH-C-07: Solubility Curves (g per 100 g Water), Recrystallisation Mass & Paper/TLC Chromatography R_f (Sample)Chemistry

00:00.0

SUB-90 ZONE (<40S)

0.0s40s Sub-9090s ESAT Budget150s Classroom

Question 1 of 1ARCH-C-07 (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-07•Standard 5-Option

or press Enter to start