What does pH measure?

pH measures the hydrogen ion concentration in a solution. It's a logarithmic scale from 0-14, where each whole number represents a 10-fold change in acidity.

At 25°C, pure water has equal amounts of H+ and OH- ions ([H+] = 10^-7 M). This defines neutral pH. Temperature affects this neutrality point.

Can pH be below 0 or above 14?

Yes, very concentrated acids can have negative pH, and strong bases can exceed pH 14. These are extreme cases outside the typical measurement range.

What is pH and why does it matter?

pH quantifies the concentration of hydrogen ions in a solution on a logarithmic scale. It directly reflects a solution's acidity or basicity, and is critical in chemistry, biology, medicine, and environmental science. Even small shifts in pH can dramatically change how a chemical reaction proceeds or how living organisms function.

How do I calculate the pH of a solution?

To find pH, measure the molar concentration of hydrogen ions [H+] in the solution, then apply: pH = −log₁₀([H+]). For example, if [H+] = 0.001 mol/L, then pH = −log(0.001) = 3. If you already know the pH and want the concentration, rearrange to [H+] = 10^(−pH).

What is the difference between pH and pOH?

pH measures hydrogen ion [H+] concentration, while pOH measures hydroxide ion [OH-] concentration: pOH = −log([OH-]). In aqueous solutions at 25°C, the two are always linked by pH + pOH = 14. So if you know one, you can instantly calculate the other.

What are some real-world examples of pH?

Common pH examples: pure water is 7 (neutral); human blood is around 7.4 (slightly basic); stomach acid ranges from 1 to 2 (strongly acidic); coffee is typically 4 to 5; baking soda solution is about 8.3; bleach is around 12 to 13. Battery acid can approach 0 and concentrated drain cleaners can reach 14.

pH Calculator - Bunny Calculator

Complete User Guide

Our pH Calculator converts between pH values and concentration. Here's how to use it:

Step 1: Choose your calculation type: pH from concentration, or concentration from pH.

Step 2: Enter the known value ([H+] concentration in mol/L, or pH value).

Step 3: Click 'Calculate' to see the results.

The calculator displays: - pH value - Hydrogen ion concentration [H+] - Hydroxide ion concentration [OH-] - pOH value - Acidic/basic/neutral nature

The Mathematical Formula

pH = -log10[H+]

pH formulas are based on logarithms:

pH = -log10[H+]

[H+] = 10^(-pH)

Relationship between pH and pOH: pH + pOH = 14 (at 25°C)

[H+] × [OH-] = 10^(-14) (water ion product constant)

pH Scale: - Acidic: pH < 7 (higher [H+]) - Neutral: pH = 7 ([H+] = [OH-]) - Basic: pH > 7 (lower [H+])

About pH Calculator

pH (potential of hydrogen) is a numeric scale that quantifies how acidic or basic an aqueous solution is. It is defined as the negative base-10 logarithm of the hydrogen ion concentration: pH = −log₁₀([H⁺]). Because the scale is logarithmic, a difference of one pH unit represents a tenfold change in ion concentration — making pH 3 ten times more acidic than pH 4.

The scale typically runs from 0 to 14, though highly concentrated acids or bases can push beyond these limits. Solutions below pH 7 are acidic, above pH 7 are basic (alkaline), and pH 7 is neutral — the value of pure water at 25°C. Alongside pH, chemists also use pOH to describe hydroxide ion concentration, related by the equation: pH + pOH = 14.

Three major theories define what acids and bases actually are. Arrhenius theory describes acids as hydrogen ion donors and bases as hydroxide ion donors in water. The broader Brønsted–Lowry model defines acids as proton donors and bases as proton acceptors. Lewis theory, the most general, treats acids as electron-pair acceptors and bases as electron-pair donors.

The human body maintains tightly regulated pH levels. Blood must stay between 7.35 and 7.45 for normal function. The stomach is far more acidic, with gastric fluid reaching as low as pH 1 to support digestion. Environmental monitoring of water sources also depends on pH measurement, since aquatic life is highly sensitive to deviations from natural pH ranges.

Frequently Asked Questions

pH Calculator