ARCH-C-08: Strong Acid Factor-of-10 pH Dilutions, Weak vs. Strong Acid Foils & Salt Preparation Methods

Full 15-Q Timed Drill

Step 1 of 6 • The Core Idea

ARCH-C-08: Why the 130s Classroom Method Fails Under the 90s Clock

Standard Classroom Method (Too Slow)~130s (Blows 90s Clock)

The dilution factor is

\frac{V_{\text{final}}}{V_{\text{init}}} = \frac{1000}{10} = 100 = 10^2

. Therefore

[\text{H}^+]

decreases by a factor of

10^2

from

10^{-1}\text{ mol dm}^{-3}

10^{-3}\text{ mol dm}^{-3}

, increasing the

\text{pH}

2

units from

1.0

3.0

(~85s).

The Fast ShortcutTarget: 35s (Saves 95s)

Line 1 (Dilution Power of 10):

\frac{1000}{10} = 10^2 \implies \Delta\text{pH} = +2

.
**Line 2 (Add to Initial

\text{pH}

):**

1.0 + 2 = 3.0

(15s).

Where Students Lose Time: In 10 past UAT-UK questions (4.44% of Chemistry), candidates lose 95s by treating the base-10 logarithmic ph scale as a linear concentration ratio. Instead, apply C9 with Maths 1 skill M2.6.

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