- What is pH?
- pH is the negative base-10 logarithm of the hydrogen-ion concentration in moles per litre: pH = −log₁₀([H⁺]). A pH of 7 is neutral at 25°C. Below 7 is acidic (more H⁺); above 7 is basic (less H⁺, more OH⁻). The scale is logarithmic — pH 3 has 10× more H⁺ than pH 4, and 10,000× more H⁺ than pH 7.
- How do I get [H⁺] from pH?
- Invert the log: [H⁺] = 10^(−pH). pH 7 gives [H⁺] = 10⁻⁷ M. pH 2 gives [H⁺] = 10⁻² M = 0.01 M. The calculator handles the math and lets you display the answer in M, mM, μM, or nM — useful when working with dilute biological buffers.
- Why does the unit matter — M vs mM vs μM vs nM?
- Concentration units are powers of 10 apart and chemists/biologists work in different ranges. Textbook acid–base problems use molar (M). Cell-culture media run in millimolar (mM). Drug dosing and enzyme assays use micromolar (μM). Receptor binding and DNA hybridisation use nanomolar (nM). The pH stays the same regardless of the unit you typed — the calculator converts to mol/L internally before taking the log.
- What is pOH and how does it relate to pH?
- pOH is the negative log of the hydroxide-ion concentration: pOH = −log₁₀([OH⁻]). At 25°C, water self-ionises with a constant Kw = [H⁺][OH⁻] = 10⁻¹⁴, so pH + pOH = 14. If you know one, you know the other. The pOH ↔ pH tab does this 14-complement instantly in either direction.
- Can pH go below 0 or above 14?
- Yes — the 0–14 range is a convention, not a hard limit. Concentrated sulfuric acid can reach pH around −3. Saturated sodium hydroxide approaches pH 15. The calculator computes any value and shows a small note when you're outside 0–14, so you know it's mathematically real but uncommon. Don't write 'pH 15' on a lab report without acknowledging it.
- Does pH depend on temperature?
- Yes — Kw varies with temperature, so neutral pH shifts. At 25°C, neutral water is pH 7.00. At 0°C it's about pH 7.47; at 100°C it's about pH 6.13. Water is still neutral in all three cases — neutral just means [H⁺] = [OH⁻]. This calculator assumes 25°C, which is the convention for most homework and bench-chemistry problems.
- How is this different from a strong-acid pH calculator?
- This tool takes the [H⁺] concentration you already know and computes pH. A strong-acid pH calculator takes the molarity of an acid like HCl or H₂SO₄ and assumes complete dissociation to get [H⁺] first, then computes pH. They're two different jobs. We'll ship the strong-acid version as a separate microapp so each tool stays one thing.
- Is my data saved anywhere?
- No. The math runs in your browser — no servers, no logs, no accounts.
