pH and Acid-Base Calculator
ANA›Life Services Authority›National Calculator Authority›pH and Acid-Base Calculator
.calc-container { max-width: 640px; margin: 2rem 0; padding: 1.5rem; background: #fff; border: 1px solid #ddd; border-radius: 8px; box-shadow: 0 1px 3px rgba(0,0,0,0.06); font-family: system-ui, -apple-system, sans-serif; } .calc-container h3 { font-family: Georgia, serif; font-size: 1.15rem; color: #1a1a1a; margin-bottom: 1rem; padding-bottom: 0.5rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-row { display: flex; align-items: center; gap: 0.75rem; margin-bottom: 0.75rem; flex-wrap: wrap; } .calc-row label { min-width: 160px; font-size: 0.9rem; color: #333; font-weight: 500; } .calc-row input[type="number"], .calc-row select { flex: 1; min-width: 120px; max-width: 200px; padding: 0.5rem 0.6rem; border: 1px solid #ccc; border-radius: 4px; font-size: 0.9rem; font-family: system-ui, sans-serif; color: #1a1a1a; background: #fafaf8; } .calc-row input:focus, .calc-row select:focus { outline: none; border-color: var(--ac, #3d5a80); box-shadow: 0 0 0 2px rgba(26,74,138,0.12); } .calc-row .unit { font-size: 0.82rem; color: #888; min-width: 30px; } .calc-btn { display: inline-block; margin-top: 0.5rem; padding: 0.55rem 1.5rem; background: var(--ac, #3d5a80); color: #fff; border: none; border-radius: 4px; font-size: 0.9rem; font-weight: 600; cursor: pointer; font-family: system-ui, sans-serif; } .calc-btn:hover { opacity: 0.9; } .calc-result { margin-top: 1.25rem; padding: 1rem 1.25rem; background: #f0f6fc; border-left: 3px solid var(--ac, #3d5a80); border-radius: 0 6px 6px 0; display: none; } .calc-result.visible { display: block; } .calc-result-label { font-size: 0.78rem; text-transform: uppercase; letter-spacing: 0.06em; color: #666; margin-bottom: 0.25rem; } .calc-result-value { font-size: 1.6rem; font-weight: 700; color: var(--ac, #3d5a80); } .calc-result-detail { font-size: 0.85rem; color: #555; margin-top: 0.5rem; line-height: 1.5; } .calc-note { margin-top: 1rem; font-size: 0.8rem; color: #888; font-style: italic; } .calc-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 0.75rem; margin-top: 0.75rem; } .calc-grid-item { padding: 0.6rem 0.8rem; background: #f8f9fa; border-radius: 4px; border: 1px solid #eee; } .calc-grid-item .label { font-size: 0.75rem; color: #888; text-transform: uppercase; letter-spacing: 0.04em; } .calc-grid-item .value { font-size: 1.1rem; font-weight: 600; color: #1a1a1a; } @media (max-width: 720px) { .calc-row { flex-direction: column; align-items: flex-start; gap: 0.3rem; } .calc-row label { min-width: auto; } .calc-row input[type="number"], .calc-row select { max-width: 100%; width: 100%; } .calc-grid { grid-template-columns: 1fr; } } .calc-chart { margin: 1rem 0; text-align: center; } .calc-chart svg { max-width: 100%; height: auto; } .calc-chart-legend { display: flex; flex-wrap: wrap; justify-content: center; gap: 0.6rem 1.2rem; margin-top: 0.6rem; font-size: 0.8rem; color: #555; } .calc-chart-legend span { display: inline-flex; align-items: center; gap: 0.3rem; } .calc-chart-legend i { display: inline-block; width: 10px; height: 10px; border-radius: 2px; font-style: normal; } .calc-related { max-width: 640px; margin: 2rem 0 1rem; padding: 1.25rem 1.5rem; background: #f8f9fa; border: 1px solid #e8e8e8; border-radius: 8px; } .calc-related h3 { font-family: Georgia, serif; font-size: 1rem; color: #1a1a1a; margin: 0 0 0.75rem; padding-bottom: 0.4rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-related-list { list-style: none; padding: 0; margin: 0 0 0.75rem; display: grid; grid-template-columns: 1fr 1fr; gap: 0.4rem 1.5rem; } .calc-related-list li a { font-size: 0.88rem; color: var(--ac, #3d5a80); text-decoration: none; } .calc-related-list li a:hover { text-decoration: underline; } .calc-browse-all { margin: 0.5rem 0 0; font-size: 0.9rem; font-weight: 600; } .calc-browse-all a { color: var(--ac, #3d5a80); text-decoration: none; } .calc-browse-all a:hover { text-decoration: underline; } @media (max-width: 720px) { .calc-related-list { grid-template-columns: 1fr; } }
pH and Acid-Base Calculator
Calculate pH, pOH, [H⁺], [OH⁻], and acid/base classification for aqueous solutions at 25°C.
Calculate From
pH value pOH value Hydrogen ion concentration [H⁺] (mol/L) Hydroxide ion concentration [OH⁻] (mol/L) Weak acid (Ka and concentration) Weak base (Kb and concentration)
pH Value
dimensionless (0–14)
pOH Value
dimensionless (0–14)
Hydrogen Ion Concentration [H⁺]
mol/L
Hydroxide Ion Concentration [OH⁻]
mol/L
Acid Dissociation Constant (Ka)
mol/L
Initial Acid Concentration (C)
mol/L
Base Dissociation Constant (Kb)
mol/L
Initial Base Concentration (C)
mol/L
Calculate Results will appear here.
function phUpdateInputs() { var type = document.getElementById('ph-calc-type').value; var sections = ['ph-input-ph','ph-input-poh','ph-input-h-conc','ph-input-oh-conc','ph-input-weak-acid','ph-input-weak-base']; sections.forEach(function(s){ document.getElementById(s).style.display='none'; }); var map = { 'ph':'ph-input-ph', 'poh':'ph-input-poh', 'h_conc':'ph-input-h-conc', 'oh_conc':'ph-input-oh-conc', 'weak_acid':'ph-input-weak-acid', 'weak_base':'ph-input-weak-base' }; document.getElementById(map[type]).style.display='block'; document.getElementById('ph-result').innerHTML = 'Results will appear here.'; }
function phClassify(pH) { if (pH 14) return { label: 'Out of typical range', color: '#888' }; if (pH = 6.9999) return { label: 'Neutral', color: '#27ae60' }; if (pH ' + exp + ''; }
function phCalc() { var type = document.getElementById('ph-calc-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-ph-value').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 for aqueous solutions at 25°C.'); 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-poh-value').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 for aqueous solutions at 25°C.'); pOH = raw; pH = 14 - pOH; H = Math.pow(10, -pH); OH = Math.pow(10, -pOH);
} else if (type === 'h_conc') { var raw = parseFloat(document.getElementById('ph-h-conc').value); if (isNaN(raw) || raw 1) throw new Error('[H⁺] cannot exceed 1 mol/L for dilute aqueous solutions (pH would be negative).'); H = raw; pH = -Math.log10(H); pOH = 14 - pH; OH = Kw / H;
} else if (type === 'oh_conc') { var raw = parseFloat(document.getElementById('ph-oh-conc').value); if (isNaN(raw) || raw 1) throw new Error('[OH⁻] cannot exceed 1 mol/L for dilute aqueous solutions.'); OH = raw; pOH = -Math.log10(OH); pH = 14 - pOH; H = Kw / OH;
} else if (type === 'weak_acid') { var Ka = parseFloat(document.getElementById('ph-ka').value); var C = parseFloat(document.getElementById('ph-acid-conc').value); if (isNaN(Ka) || Ka = C) throw new Error('Ka must be less than C for the weak acid approximation to be meaningful. Consider using a strong acid model.'); // Exact quadratic: [H+]^2 + Ka[H+] - KaC = 0 // x = (-Ka + sqrt(Ka^2 + 4KaC)) / 2 H = (-Ka + Math.sqrt(Ka * Ka + 4 * Ka * C)) / 2; pH = -Math.log10(H); pOH = 14 - pH; OH = Kw / H; var percentDiss = (H / C) * 100; var approxValid = (H / C) = C) throw new Error('Kb must be less than C for the weak base approximation to be meaningful.'); // Exact quadratic: [OH-]^2 + Kb[OH-] - KbC = 0 OH = (-Kb + Math.sqrt(Kb * Kb + 4 * Kb * C)) / 2; pOH = -Math.log10(OH); pH = 14 - pOH; H = Kw / OH; var percentDiss = (OH / C) * 100; var approxValid = (OH / C) ' + cls.label + '';
var html = '### Results '; html += ''; html += 'PropertyValue'; html += 'pH' + pH.toFixed(4) + ''; html += 'pOH' + pOH.toFixed(4) + ''; html += '[H⁺]' + phFormatSci(H) + ' mol/L'; html += '[OH⁻]' + phFormatSci(OH) + ' mol/L'; html += 'Classification' + badge + '';
if (type === 'weak_acid' || type === 'weak_base') { html += '% Dissociation' + percentDiss.toFixed(2) + '%'; html += '5% Approximation Valid?' + (approxValid ? '✅ Yes' : '⚠️ No — quadratic used') + ''; }
html += ''; resultDiv.innerHTML = html;
} catch(e) { resultDiv.innerHTML = '⚠ ' + e.message + ''; } }
#### Formulas Used
Core relationships (at 25°C, Kw = 1×10⁻¹⁴):
Weak acid (exact quadratic):
Weak base (exact quadratic):
#### Assumptions & References
- All calculations assume dilute aqueous solutions at 25°C (298.15 K).
- The weak acid/base model uses the exact quadratic formula, not the 5% approximation, ensuring accuracy at all concentrations.
- References: Atkins & de Paula, Physical Chemistry, 10th ed.; Zumdahl, Chemistry, 9th ed.; IUPAC recommendations for pH (2002).
More Calculators
- Hazardous Waste Disposal Cost Calculator
- Speedrun Split Time & Pace Calculator
- Construction Debris Volume and Dumpster Size Calculator
- Countertop Square Footage Calculator
- Countertop Material Cost Comparison Calculator
- Tile Countertop Layout and Grout Calculator
- Cyber Risk Score Calculator
- Telehealth Visit Cost Savings Calculator
- Telehealth vs In-Person Care Cost Comparison Calculator
- Remote Patient Monitoring Frequency Calculator
- Telehealth Eligibility Checker
- Home Maintenance Budget Calculator
Read Next
Telehealth Eligibility Checker ANA › Life Services Authority › National Calculator Authority › Telehealth Eligibility Checker .calc-container { max-width:...
Study Time Planner Authority Network America › Life Services Authority › National Calculator Authority .calc-container { max-width: 640px;...