Crowded ions, low pH
The more H₃O⁺ ions, the lower the pH.
Count the ions
Two acids are tested with a pH paper. Acid A has many H₃O⁺ ions in the glass. Acid B has few.
Which acid will show the lower pH?
What this lesson covers
The idea
The higher the hydronium ion concentration of a solution, the lower its pH value.
Count the ions
Two acids are tested with a pH paper. Acid A has many H₃O⁺ ions in the glass. Acid B has few.
Which acid will show the lower pH?
- Acid A, with many H₃O⁺ ions
- Acid B, with few H₃O⁺ ions
- Both the same
Slide the ions
Slide to more H₃O⁺ ions, then back to fewer. Watch the marker on the pH bar.
More ions, lower pH
The higher the hydronium ion concentration of a solution, the lower its pH value.
The two move in opposite directions: when one goes up, the other goes down.
- H₃O⁺ ions | pH | Universal indicator
- more | lower | towards red
- fewer | higher | towards green
Notes
The higher the hydronium ion concentration of a solution, the lower its pH value.
Check yourself
A solution has more H₃O⁺ ions. Its pH is …
Solution X has pH 2. Solution Y has pH 5. Which has more H₃O⁺ ions?
Water is added to an acid, so the H₃O⁺ ions are spread out. The pH …
- higher. It is the opposite: more H₃O⁺ gives a lower pH.
- always 7. pH 7 is neutral. A solution with more H₃O⁺ is acidic.
- lower — correct. Yes! More H₃O⁺, lower pH.
- X — correct. Yes! The lower pH has more H₃O⁺.
- Y. Y has the higher pH, so it has fewer H₃O⁺.
- Both the same. Different pH means different amounts of H₃O⁺.
- goes down. Dilution gives fewer H₃O⁺ per unit volume, so the pH goes up.
- goes up — correct. Yes! Fewer H₃O⁺ per unit volume means a higher pH.
- does not change. The H₃O⁺ concentration falls, so the pH changes.