{"success":true,"version":"v1","request":{"tool":"get_calculator_schema","calculator_id":"henderson-hasselbalch"},"result":{"entity_type":"calculator","id":"henderson-hasselbalch","calculator_id":"henderson-hasselbalch","canonical_url":"https://tttkmbb.com/chemistry/henderson-hasselbalch","name":"Henderson–Hasselbalch Calculator","title":"Henderson–Hasselbalch Calculator – Buffer pH from pKa and Conjugate Base/Acid Ratio","category":"chemistry","category_name":"Chemistry","tool_name":"calculate_henderson_hasselbalch_ph","featured_mcp_tool":false,"description":"Computes the pH of a buffer from the acid's pKa and the concentrations (or ratio) of conjugate base and weak acid with the Henderson–Hasselbalch equation, or the base/acid ratio required for a target pH.","use_when":"You are preparing or analysing a buffer and need its pH from pKa and composition, or the acid-to-base ratio that gives a chosen pH.","do_not_use_when":"The solution is a strong acid or base (use ph), the buffer is very dilute (below about 1 mM) or the pH is more than about 1.5 units from pKa, where the approximation breaks down.","inputs":[{"name":"pka","label":"pKa","type":"number","required":true,"min":-10,"max":25,"description":"Acid dissociation constant exponent of the weak acid (e.g. acetic acid 4.76, H2PO4⁻ 7.21, NH4⁺ 9.25, carbonic acid in blood 6.1).","example":4.76},{"name":"base_concentration","label":"Conjugate base concentration [A⁻]","type":"number","required":false,"exclusive_min":0,"description":"Concentration of the conjugate base (e.g. acetate), in any unit shared with acid_concentration.","example":0.1},{"name":"acid_concentration","label":"Weak acid concentration [HA]","type":"number","required":false,"exclusive_min":0,"description":"Concentration of the weak acid (e.g. acetic acid), same unit as base_concentration.","example":0.1},{"name":"ratio_base_to_acid","label":"Ratio [A⁻]/[HA]","type":"number","required":false,"exclusive_min":0,"description":"Base-to-acid ratio; alternative to giving both concentrations."},{"name":"ph","label":"Target pH","type":"number","required":false,"min":-2,"max":16,"description":"When given, the calculator solves for the [A⁻]/[HA] ratio that produces this pH instead of computing pH."}],"outputs":[{"name":"ph","label":"pH","type":"number","decimals":3,"description":"Buffer pH = pKa + log10([A⁻]/[HA])."},{"name":"ratio_base_to_acid","label":"[A⁻]/[HA]","type":"number","decimals":4,"description":"Conjugate base to weak acid ratio, given or solved."},{"name":"log_ratio","label":"log10 ratio","type":"number","decimals":4,"description":"pH − pKa."},{"name":"base_percent","label":"Base form","type":"number","unit":"%","decimals":2,"description":"Share of the pair present as conjugate base: 100 × ratio / (1 + ratio)."},{"name":"acid_percent","label":"Acid form","type":"number","unit":"%","decimals":2,"description":"Share present as undissociated acid."},{"name":"base_concentration","label":"[A⁻]","type":"number","decimals":6,"description":"Conjugate base concentration (when known or derivable from acid_concentration and the ratio)."},{"name":"acid_concentration","label":"[HA]","type":"number","decimals":6,"description":"Weak acid concentration (when known or derivable from base_concentration and the ratio)."},{"name":"buffer_range","label":"Useful buffer range","type":"string","decimals":4,"description":"pKa ± 1, the range in which the buffer resists pH change effectively."},{"name":"solved_for","label":"Solved for","type":"string","decimals":4,"description":"ph or ratio_base_to_acid."}],"input_schema":{"type":"object","properties":{"pka":{"description":"Acid dissociation constant exponent of the weak acid (e.g. acetic acid 4.76, H2PO4⁻ 7.21, NH4⁺ 9.25, carbonic acid in blood 6.1).","type":"number","minimum":-10,"maximum":25,"examples":[4.76]},"base_concentration":{"description":"Concentration of the conjugate base (e.g. acetate), in any unit shared with acid_concentration.","type":"number","exclusiveMinimum":0,"examples":[0.1]},"acid_concentration":{"description":"Concentration of the weak acid (e.g. acetic acid), same unit as base_concentration.","type":"number","exclusiveMinimum":0,"examples":[0.1]},"ratio_base_to_acid":{"description":"Base-to-acid ratio; alternative to giving both concentrations.","type":"number","exclusiveMinimum":0},"ph":{"description":"When given, the calculator solves for the [A⁻]/[HA] ratio that produces this pH instead of computing pH.","type":"number","minimum":-2,"maximum":16}},"additionalProperties":false,"required":["pka"]},"output_schema":{"type":"object","properties":{"ph":{"description":"Buffer pH = pKa + log10([A⁻]/[HA]).","type":"number"},"ratio_base_to_acid":{"description":"Conjugate base to weak acid ratio, given or solved.","type":"number"},"log_ratio":{"description":"pH − pKa.","type":"number"},"base_percent":{"description":"Share of the pair present as conjugate base: 100 × ratio / (1 + ratio). Unit: %.","type":"number","x-unit":"%"},"acid_percent":{"description":"Share present as undissociated acid. Unit: %.","type":"number","x-unit":"%"},"base_concentration":{"description":"Conjugate base concentration (when known or derivable from acid_concentration and the ratio).","type":"number"},"acid_concentration":{"description":"Weak acid concentration (when known or derivable from base_concentration and the ratio).","type":"number"},"buffer_range":{"description":"pKa ± 1, the range in which the buffer resists pH change effectively.","type":"string"},"solved_for":{"description":"ph or ratio_base_to_acid.","type":"string"}}},"formula":"pH = pKa + log10([A⁻] / [HA]); ratio = [A⁻]/[HA] = 10^(pH − pKa); base_percent = 100 × ratio / (1 + ratio)","method":"Valid when both buffer components are much more concentrated than [H⁺] and [OH⁻] and activity coefficients are close to 1; for accurate work use the pKa at the working temperature and ionic strength.","sources":[{"name":"OpenStax Chemistry 2e – 14.6 Buffers","url":"https://openstax.org/books/chemistry-2e/pages/14-6-buffers","type":"textbook","retrieved_at":"2026-09-24"},{"name":"Wikipedia – Henderson–Hasselbalch equation","url":"https://en.wikipedia.org/wiki/Henderson%E2%80%93Hasselbalch_equation","type":"reference","retrieved_at":"2026-09-24"}],"freshness":{"type":"static","max_age_seconds":null,"note":"Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output."},"examples":[{"name":"Acetate buffer 0.2 M acetate / 0.1 M acetic acid","inputs":{"pka":4.76,"base_concentration":0.2,"acid_concentration":0.1},"expected":{"ph":5.061,"ratio_base_to_acid":2,"log_ratio":0.301,"base_percent":66.67,"buffer_range":"3.76 – 5.76","solved_for":"ph"},"url":"https://tttkmbb.com/api/v1/calculate/henderson-hasselbalch?pka=4.76&base_concentration=0.2&acid_concentration=0.1"},{"name":"Bicarbonate ratio at blood pH 7.4","inputs":{"pka":6.1,"ph":7.4},"expected":{"ratio_base_to_acid":19.953,"log_ratio":1.3,"base_percent":95.23,"acid_percent":4.77,"solved_for":"ratio_base_to_acid"},"url":"https://tttkmbb.com/api/v1/calculate/henderson-hasselbalch?pka=6.1&ph=7.4"}],"faq":[{"q":"Do I need molar concentrations?","a":"No. Only the ratio matters, so moles, mmol or any concentration unit work as long as both components use the same unit."},{"q":"Why does my measured pH differ from the calculated value?","a":"pKa shifts with temperature and ionic strength, and the equation ignores activity coefficients; deviations of 0.1–0.2 pH units are common in concentrated buffers."}],"tags":["henderson hasselbalch","buffer ph","pka","conjugate base ratio","buffer preparation"],"related":[{"calculator_id":"ph","reason":"pH of strong acids and bases without a buffer."},{"calculator_id":"molarity","reason":"Prepare the acid and base components at the required concentrations."},{"calculator_id":"logarithm","reason":"log10 arithmetic used in the equation."}],"links":{"html":"https://tttkmbb.com/chemistry/henderson-hasselbalch","markdown":"https://tttkmbb.com/chemistry/henderson-hasselbalch.md","json":"https://tttkmbb.com/chemistry/henderson-hasselbalch.json","api":"https://tttkmbb.com/api/v1/calculate/henderson-hasselbalch","schema":"https://tttkmbb.com/api/v1/calculators/henderson-hasselbalch","openapi":"https://tttkmbb.com/openapi.json","mcp":"https://tttkmbb.com/mcp"},"version":"v1","updated_at":"2026-09-24"},"timestamp":"2026-09-23T23:35:04Z","next_actions":[{"tool":"run_calculator","calculator_id":"henderson-hasselbalch","reason":"Run Henderson–Hasselbalch Calculator with the inputs above."}],"links":{"markdown":"https://tttkmbb.com/chemistry/henderson-hasselbalch.md"}}