Why can one tiny pH step make such a huge difference?
Your stomach acid, soap, and tap water can all look similar, but your pH scale shows they are chemically very different.
When you talk about pH, you are using a number that tells you how acidic or alkaline a water-based solution is by tracking how much H⁺(aq) is present.
The equation you need is pH = -log [H⁺], where [H⁺] is measured in mol dm⁻³.
The weird part is that your pH scale is not linear. If your pH drops by 1, the hydrogen ion concentration becomes 10 times larger. So if you compare pH 3 with pH 4, the pH 3 solution has 10× more H⁺, and if you compare pH 2 with pH 4, it has 100× more H⁺.
That means lower numbers are much more acidic, not just a little bit more. Higher pH means fewer hydrogen ions, so your solution is more basic. This is why a small pH change can represent a massive chemical change.
If your solution has [H⁺] = 1.0 × 10⁻³ mol dm⁻³, then you calculate pH = -log₁₀(1.0 × 10⁻³) = 3.0.
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