Solution Concentration Calculator (% and mol/dm³)
Calculate the percentage or molar concentration of a solution. Enter the solute mass, solution mass or molar data — instant result. Free chemistry calculator.
Current for 2026Methodology →
pH Solution Calculator
The pH solution calculator lets you instantly compute the pH from the hydrogen ion concentration [H+], determine the H+ or OH- concentration from a known pH, or convert a pOH value to pH. The pH scale (0-14) describes the acidity of a solution: values below 7 indicate an acidic solution, 7 is neutral (e.g. pure water), and above 7 is basic (alkaline). Knowledge of pH is essential in chemistry, biology, pharmacy, water quality analysis and agriculture. The calculator also shows the complementary quantity (pOH, cH or cOH) and the solution character automatically.
Na tej stronie
How we calculate pH
Mode 1 (pH from concentration): pH = -log10(cH), where cH is the H+ concentration in mol/L. Then pOH = 14 - pH. Character: acidic if pH < 7, neutral if pH = 7, basic if pH > 7. Mode 2 (concentration from pH): cH = 10^(-pH), cOH = 10^(-(14-pH)). The relationship follows from the water ion product Kw = cH × cOH = 10^-14 at 25°C. Mode 3 (pH from pOH): pH = 14 - pOH, then cH = 10^(-pH). All formulas use the relation pH + pOH = 14. Results are rounded to 4 significant figures.
Example: pH of hydrochloric acid
Example 1 — pH from concentration: Hydrochloric acid HCl at cH = 0.01 mol/L is a strong acid fully dissociated. pH = -log10(0.01) = 2. The solution is acidic; pOH = 14 - 2 = 12. Example 2 — concentration from pH: For a solution with pH = 3, the H+ concentration is cH = 10^(-3) = 0.001 mol/L, and the OH- concentration is cOH = 10^(-11) mol/L. Example 3 — pH from pOH: A NaOH solution with pOH = 4 has pH = 14 - 4 = 10. This is a basic (alkaline) solution.
Frequently asked questions about pH
What is pH?
pH is a measure of the acidity or alkalinity of an aqueous solution. It is defined as the negative base-10 logarithm of the hydrogen ion concentration: pH = -log10[H+]. The pH scale runs from 0 to 14 — values below 7 indicate an acidic solution, 7 is neutral (e.g. pure water), and above 7 is basic (alkaline).
What is pOH and how is it related to pH?
pOH is a measure of the hydroxide ion OH- concentration in a solution: pOH = -log10[OH-]. At 25°C the relationship pH + pOH = 14 holds. This means that if you know the pH, you can easily calculate the pOH and vice versa.
How do I calculate pH from H+ concentration?
Use the formula: pH = -log10(cH), where cH is the H+ concentration in mol/L (mol/dm³). For example, for cH = 0.01 mol/L: pH = -log10(0.01) = 2. The solution is therefore acidic.
What are typical examples of acidic solutions and their pH?
Common acidic solutions: lemon juice pH ≈ 2-3, vinegar pH ≈ 2.5-3.5, coffee pH ≈ 5, rain water pH ≈ 5.6. The lower the pH, the more acidic the solution and the higher the H+ concentration.
What are typical examples of basic solutions and their pH?
Common basic (alkaline) solutions: baking soda (NaHCO3) pH ≈ 8.3, washing soda (Na2CO3) pH ≈ 11, bleach pH ≈ 12-13, sodium hydroxide (NaOH) pH ≈ 14. The higher the pH, the more basic the solution.
What is the water ion product (Kw)?
Kw is the water ion product, equal to the equilibrium constant of the water auto-ionisation reaction: H2O ⇌ H+ + OH-. At 25°C, Kw = [H+] × [OH-] = 10^-14 (mol/L)². From this it follows that pH + pOH = 14 for pure water and dilute aqueous solutions at this temperature.
How is pH measured in practice?
pH can be measured using indicator papers (litmus, pH paper strips), electronic pH meters with glass electrodes, and coloured indicators (phenolphthalein, methyl orange). The most accurate method is the electrochemical one using a pH meter.
Why is the pH scale logarithmic?
The logarithmic scale arises from the enormous range of H+ concentrations — from 1 mol/L (strong acid) to 10^-14 mol/L (strong base). The logarithm compresses these values onto a convenient 0-14 scale instead of dealing with very small numbers. A change of 1 pH unit corresponds to a 10-fold change in H+ concentration.
Can pH be negative or greater than 14?
Yes, in theory pH can exceed the 0-14 range at very high acid or base concentrations. For example, concentrated sulfuric acid may have a pH of about -3. However, the concept of pH is typically applied to aqueous solutions with H+ concentrations in the range 1-10^-14 mol/L.
How does pH affect chemical reactions and living organisms?
pH is critical in biochemistry — enzymes operate within a narrow pH range, and human blood maintains pH 7.35-7.45. In agriculture, soil pH determines nutrient availability. In industry, pH controls reaction rates, product stability and corrosion processes.
Results are for informational and educational purposes. The calculator assumes a temperature of 25°C (298 K), at which Kw = 10^-14. At other temperatures Kw changes. Before laboratory or industrial use, follow the appropriate analytical procedure.
Related calculators
Dilution Calculator (C1V1 = C2V2)
Calculate concentration after dilution, final volume, original concentration or sample volume. C1*V1=C2*V2 dilution formula — instant free results.