lesson
Updated 6 days ago Β· 1 view
Stomach acid has a pH around 1, while pure water is pH 7. That doesn't mean stomach acid is just 6 times strongerβit contains one million times more acid ions!
What pH Actually Measures
The pH scale measures hydrogen ion concentration, written as [H+], which tells us how acidic or alkaline a solution is.
In 1909, Danish chemist SΓΈren SΓΈrensen invented the pH scale while controlling beer fermentation, needing a simple way to write out impossibly tiny numbers like 0.0000001Β mol/dm3.
πA clean visual diagram showing three test tubes representing pH 1, pH 2, and pH 3. Each tube contains red dots representing hydrogen ions [H+]. Tube pH 1 has 100 dots (dense), Tube pH 2 has 10 dots (moderate), Tube pH 3 has 1 dot (sparse). Below each tube, show a label with pH value and relative concentration: 'pH 1: 100x', 'pH 2: 10x', 'pH 3: 1x'. Use an arrow between tubes showing a division by 10 as pH increases.
So what exact mathematical change happens to the hydrogen ions every time the pH shifts by just one unit?
The Tenfold Factor Rule
A change of 1 whole pH unit always corresponds to a tenfold (10Γ) change in hydrogen ion concentration.
Because pH is an inverse scale, decreasing the pH by 1 unit multiplies [H+] by 10, while increasing the pH by 1 unit divides [H+] by 10.
πAn interactive-style step ladder diagram showing pH values from 4 to 1. Stepping down from pH 4 to pH 3 shows a curved green arrow labeled 'Γ 10 [H+] (10x more acidic)'. Stepping down from pH 3 to pH 2 shows another arrow labeled 'Γ 10 [H+]'. Stepping up from pH 1 to pH 2 shows a purple arrow labeled 'Γ· 10 [H+]'. Highlight the inverse relationship clearly.
What happens when a solution's pH changes by more than one whole number?
Multiple Steps and Powers of 10
For a change of n whole pH units, the hydrogen ion concentration changes by a factor of 10n.