pH and pOH Calculator
ANA›Life Services Authority›National Calculator Authority›pH and pOH Calculator
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pH and pOH Calculator
Calculate pH, pOH, [H⁺], and [OH⁻] from any one known value for aqueous solutions at 25°C.
Calculate from:
pH pOH Hydrogen ion concentration [H⁺] (mol/L) Hydroxide ion concentration [OH⁻] (mol/L)
pH value:
pOH value:
[H⁺] concentration (mol/L):
[OH⁻] concentration (mol/L):
Calculate
function phToggleInputs() { var type = document.getElementById("ph-input-type").value; var groups = ["ph", "poh", "hplus", "ohplus"]; groups.forEach(function(g) { document.getElementById("ph-group-" + g).style.display = (g === type) ? "" : "none"; }); document.getElementById("ph-result").style.display = "none"; }
function phCalc() { var type = document.getElementById("ph-input-type").value; var resultDiv = document.getElementById("ph-result"); var pH, pOH, H, OH; var Kw = 1e-14; // at 25°C
try { if (type === "ph") { var raw = parseFloat(document.getElementById("ph-val-ph").value); if (isNaN(raw)) throw new Error("Please enter a valid pH value."); if (raw 14) throw new Error("pH must be between 0 and 14."); pH = raw; pOH = 14 - pH; H = Math.pow(10, -pH); OH = Math.pow(10, -pOH);
} else if (type === "poh") { var raw = parseFloat(document.getElementById("ph-val-poh").value); if (isNaN(raw)) throw new Error("Please enter a valid pOH value."); if (raw 14) throw new Error("pOH must be between 0 and 14."); pOH = raw; pH = 14 - pOH; H = Math.pow(10, -pH); OH = Math.pow(10, -pOH);
} else if (type === "hplus") { var raw = parseFloat(document.getElementById("ph-val-hplus").value); if (isNaN(raw) || raw 14) throw new Error("[H⁺] concentration is outside the typical 0–14 pH range.");
} else if (type === "ohplus") { var raw = parseFloat(document.getElementById("ph-val-ohplus").value); if (isNaN(raw) || raw 14) throw new Error("[OH⁻] concentration is outside the typical 0–14 pH range."); }
var nature = pH 7 ? "Basic (Alkaline)" : "Neutral"; var color = pH 7 ? "#2980b9" : "#27ae60";
function sciNote(val) { if (val === 0) return "0"; var exp = Math.floor(Math.log10(Math.abs(val))); var coeff = val / Math.pow(10, exp); return coeff.toFixed(4) + " × 10" + exp + ""; }
resultDiv.style.display = ""; resultDiv.innerHTML = "### Results " + "" + "Property" + "Value" + "pH" + "" + pH.toFixed(4) + "" + "pOH" + "" + pOH.toFixed(4) + "" + "[H⁺] (mol/L)" + "" + sciNote(H) + "" + "[OH⁻] (mol/L)" + "" + sciNote(OH) + "" + "Nature" + "" + nature + "" + "";
} catch(e) { resultDiv.style.display = ""; resultDiv.innerHTML = "⚠ " + e.message + "
"; } }
#### Formulas Used
pH from [H⁺]: pH = −log₁₀[H⁺]
pOH from [OH⁻]: pOH = −log₁₀[OH⁻]
Relationship at 25°C (Kw = 1×10⁻¹⁴): pH + pOH = 14 [H⁺] × [OH⁻] = Kw = 1×10⁻¹⁴ mol²/L²
Reverse calculations: [H⁺] = 10−pH | [OH⁻] = 10−pOH
#### Assumptions & References
- All calculations assume aqueous solution at 25°C (298 K), where Kw = 1×10⁻¹⁴.
- The pH scale is bounded between 0 and 14 for standard dilute aqueous solutions; concentrated strong acids/bases can exceed this range.
- pH is defined as per the IUPAC recommendation: pH = −log₁₀(aH⁺), where aH⁺ is the activity of hydrogen ions.
- Reference: Atkins, P. & de Paula, J. Physical Chemistry, 10th ed.; IUPAC Gold Book — pH definition.
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