pH Calculator

pH and pOH are related by the equation: pH + pOH = 14. To calculate pH from pOH, simply subtract the pOH value from 14. For example, if pOH is 5, then pH = 14 - 5 = 9.

Ka (acid dissociation constant) is a measure of the strength of an acid. For weak acids, we use Ka to calculate the concentration of H+ ions in solution, which then allows us to calculate the pH. The larger the Ka value, the stronger the acid.

For buffer solutions, pH can be calculated using the Henderson-Hasselbalch equation: pH = pKa + log([A-]/[HA]), where [A-] is the concentration of the conjugate base and [HA] is the concentration of the weak acid. This equation is particularly useful for solutions containing a weak acid and its conjugate base.

For strong acids, pH calculation is straightforward as they completely dissociate in water. The pH is simply -log[H+]. For weak acids, we need to use the Ka value and solve a quadratic equation to find the H+ concentration, as they only partially dissociate. This is why our calculator includes separate options for acid solutions.

Our pH calculator provides accurate results based on standard chemical equations and constants. However, for very precise laboratory work, we recommend verifying results with experimental measurements, as factors like temperature and ionic strength can affect pH values.

Let's calculate the pH of a 0.1M acetic acid solution (Ka = 1.8 × 10^-5). Using our calculator, input the concentration as 0.1 and Ka as 1.8e-5. The calculator will solve the quadratic equation to find the H+ concentration and then calculate the pH. The result should be approximately 2.87, showing that this is a weak acid solution.

pH indicators are chemicals that change color at different pH ranges. When selecting an indicator, ensure its color change range includes the equivalence point pH. Common indicators include: litmus (red 4.5-8.3 blue), methyl orange (red 3.1-4.4 yellow), phenolphthalein (colorless 8.3-10.0 pink).

Polyprotic acids (like H2SO4, H3PO4) have multiple dissociation steps, each with its own Ka value. For strong polyprotic acids, all hydrogen ions dissociate nearly completely. For weak polyprotic acids, the first dissociation step usually dominates. Our calculator can handle these calculations by inputting the appropriate Ka values.

Temperature significantly affects pH because the ion product of water (Kw) changes with temperature. At 25°C, Kw = 1×10^-14, but at higher temperatures Kw increases, causing pure water's pH to deviate from 7. Additionally, acid/base dissociation constants (Ka, Kb) are temperature-dependent, so precise pH calculations must account for temperature.