pH
Acidity from hydrogen ion concentration.
Formula
Variables
Example
Neutral water: pH 7
How it works
pH is a logarithmic way to express how acidic a solution is from its hydrogen ion concentration, [H+]. Because hydrogen ion concentrations can vary over many powers of ten, taking the negative base-10 logarithm turns very small numbers into a manageable scale; a 1-unit change in pH corresponds to a 10-fold change in [H+]. Lower pH means more hydrogen ions and therefore greater acidity, while higher pH means fewer hydrogen ions and a more basic solution.
When to use it
Use this formula whenever you need to convert a measured hydrogen ion concentration into pH, such as in water quality testing, soil chemistry, aquaculture, or acid rain studies. It is also useful for comparing how strongly acidic two environmental samples are on a standard scale.
Worked example, step by step
Given [H+] = 3.2 × 10^-5 mol/L pH = -log10[H+] pH = -log10(3.2 × 10^-5) pH = -(log10 3.2 + log10 10^-5) pH = -(0.505 - 5) pH = -(-4.495) pH = 4.495 Final answer: pH ≈ 4.50
Common mistakes to avoid
- Forgetting the negative sign, which flips acidity into the wrong direction
- Using natural log instead of base-10 log
- Putting the concentration into the formula without checking that [H+] is in mol/L
Did You Know?
Each pH unit is a tenfold change in acidity.
Share this formula
More in Environmental Science
View allCarbon Footprint
BasicEmissions from energy use and an emission factor.
Wind Turbine Power
AdvancedPower extracted from wind by a turbine.
Betz Limit
AdvancedMaximum fraction of wind energy a turbine can capture.
Solar Panel Output
IntermediateEnergy output of a photovoltaic array.
Radioactive Decay
IntermediateAmount remaining after a number of half-lives.
Energy Consumption
BasicElectrical energy used over time.