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CHEMISTRY • ACIDS & BASES
pH Explorer
Connect pH and pOH to hydrogen and hydroxide concentration, compare solutions by orders of magnitude, and reason on the logarithmic scale.
● LIVE MODELpH Explorer
Classification—
pOH—
[H⁺]—
[OH⁻]—
Reference—
Challenge—
Read pH as a logarithmic concentration scale
A one-unit pH change is a tenfold change in hydrogen-ion concentration. The comparison mode reports that ratio directly instead of treating pH as an ordinary linear scale.
Fast investigations
- Compare pH 3 and pH 5 and calculate the [H⁺] ratio.
- Move symmetrically around pH 7 and compare H⁺ with OH⁻.
- Find the pH corresponding to 10⁻⁹ M hydrogen ions.
- Track how pH and pOH always sum to 14 in this 25 °C model.
LEARN WITH THE SIMULATION
Understand pH Explorer by experimenting.
START HERE
pH is a logarithmic measure based on hydrogen-ion activity, commonly approximated with concentration in introductory models. Because the scale is logarithmic, a one-unit pH change represents a tenfold change in hydrogen-ion concentration.
BUILD THE IDEA
What you should understand first
- Convert between pH and hydrogen-ion concentration.
- Use pH + pOH = 14 in the standard introductory 25°C model.
- Recognize the logarithmic meaning of pH differences.
TRY IT YOURSELF
How much does [H⁺] change when pH drops by 2 units?
- Choose a starting pH and record [H⁺].
- Lower pH by exactly 2.
- Compare the two concentrations as a ratio.
Read the visual:
A decrease of 2 pH units corresponds to a 100× increase in hydrogen-ion concentration in this model.
WHY IT WORKS 01
Convert between pH and hydrogen-ion concentration.
pH is a logarithmic measure based on hydrogen-ion activity, commonly approximated with concentration in introductory models. Because the scale is logarithmic, a one-unit pH change represents a tenfold change in hydrogen-ion concentration. Focus on the relationship between the controlled variable and the measured response rather than treating the visual change as the explanation.
WHY IT WORKS 02
Use pH + pOH = 14 in the standard introductory 25°C model.
A decrease of 2 pH units corresponds to a 100× increase in hydrogen-ion concentration in this model. Use an extreme or boundary setting after the baseline trial to check whether the same reasoning still holds.
DO NOT MIX THESE UP
Common misconception
Neutral pH is exactly 7 only under the standard introductory water model near 25°C. Concentration and activity are not identical in concentrated solutions. Strong and weak acids cannot be compared by pH alone without concentration context.
PRACTICE CHALLENGE
How much does [H⁺] change when pH drops by 2 units?
- Choose a starting pH and record [H⁺].
- Lower pH by exactly 2.
- Compare the two concentrations as a ratio.
Reveal the reasoning
A decrease of 2 pH units corresponds to a 100× increase in hydrogen-ion concentration in this model. Neutral pH is exactly 7 only under the standard introductory water model near 25°C. Concentration and activity are not identical in concentrated solutions. Strong and weak acids cannot be compared by pH alone without concentration context.
MODEL BOUNDARIES
What this simulation assumes
Every simulation simplifies reality or a mathematical system. These are the assumptions and limits to keep in mind while interpreting the results.
Model assumptions
- pH is defined from hydrogen-ion concentration using pH = −log10[H+].
- At 25 °C the simulator uses pH + pOH = 14.
- Concentrations are treated as ideal activities for this educational model.
Model limitations
- Real solutions can require activity coefficients, especially at high ionic strength.
- The pH + pOH = 14 relationship changes with temperature, and complex acid-base equilibria are not solved automatically.
CONNECT IT
Where this matters
- Water quality
- Acid-base titration
- Biological and environmental chemistry
WORDS THAT MATTER
Key vocabulary
- pH
- Negative base-10 logarithm of hydrogen-ion activity or its dilute concentration approximation.
- pOH
- Corresponding logarithmic measure for hydroxide.
- Logarithmic scale
- Scale in which equal steps represent multiplicative changes.
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