Conjugate base to acid ratio calculator
Know the base-to-acid mix a buffer needs at a given pH: at pH 4.76 with a pKa of 4.76 the ratio is exactly 1, so both forms are equal. Above the pKa the base dominates, below it the acid does. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Buffer pH
- 4.76
- Pka
- 4.76
- PH
- 4.76
- PKa
- 4.76
- Delta
- 0
- Ph minus pka
- 0
A conjugate base to acid ratio calculator turns a measured or target buffer pH and a weak-acid pKa into the composition ratio every buffer problem needs. Enter buffer pH and acid pKa; the tool returns the ratio of conjugate base to undissociated acid as ten raised to the power of pH minus pKa, a short dominance label—base-dominant, equal forms, or acid-dominant—and step-by-step substitution you can copy into a lab notebook. Homework checks, buffer prep when you know the target pH, exam review, and automated graders all need that same closed inverse Henderson–Hasselbalch formula without a spreadsheet or a full aqueous speciation package.
What the conjugate base to acid ratio means for buffers
A monoprotic buffer is a mixture of a weak acid HA and its conjugate base A− that resists large pH swings when small amounts of strong acid or base are added. The Henderson–Hasselbalch equation links buffer pH to acid strength and composition: pH equals pKa plus the base-ten logarithm of the concentration ratio of conjugate base to acid. Solving that equation for the ratio is the inverse problem this calculator answers: the ratio [A−] over [HA] equals ten raised to the power of pH minus pKa.
When buffer pH equals the pKa, the exponent is zero and the ratio is exactly one—the classic half-equivalence point where the two forms are present in equal concentration. When the buffer pH sits above the pKa, the exponent is positive, the ratio is greater than one, and the conjugate base dominates; when the buffer pH sits below the pKa, the exponent is negative, the ratio is less than one, and the undissociated acid dominates.
Absolute concentration units cancel in the ratio, so you may later scale [A−] and [HA] in moles per litre or any other consistent unit as long as their quotient matches the published ratio. What never cancels is the requirement that pKa (and pH) be finite numbers: a non-numeric pKa makes the power undefined for a real buffer design, so this tool rejects those cases instead of inventing a ratio.
Teachers and automated graders care about that rejection as much as the happy path, because a silent NaN would hide a data-entry error. The check path recomputes ten to the power of the published pH minus pKa difference with the same fixed rounding used for the ratio field, so a successful response always ships with steps you can assert in tests or lab notebooks.
Related classroom topics such as buffer capacity, polyprotic systems with multiple pKa values, or full charge-balance speciation are intentionally out of scope so this landing stays focused on the single search intent of converting a known buffer pH and acid pKa into the conjugate base to acid ratio.
Practical tips, limits, and related searches
Keep buffer pH and acid pKa inside the published absolute range so the difference pH minus pKa cannot drive ten to that power into a non-finite ratio the solver must reject. Use a measured pH from a calibrated meter when checking a real buffer, or a target pH when designing one; do not mix activity-based pH with concentration-based approximations without noting the ideal-solution assumption.
Prefer this capability when you already know buffer pH and pKa and need [A−]/[HA]; if you already know the ratio and need buffer pH, use a Henderson–Hasselbalch pH calculator instead. Round-trip intuition is easy: pKa plus log ten of the published ratio recovers the original buffer pH within the same twelve-decimal rounding for typical aqueous buffers, and confirming dominance flips correctly when you move the buffer pH across the pKa.
What you can do with it
Homework checks for buffer composition
Students enter textbook buffer pH and pKa values and compare hand-written [A−]/[HA] = 10^(pH − pKa) against a deterministic result before submitting.
Lab design of monoprotic buffers
Technicians convert a target pH and known weak-acid pKa into the required base-to-acid ratio for acetate, phosphate, or ammonia systems before mixing.
FAQ
How do you calculate the conjugate base to acid ratio from pH and pKa?
Use the inverse Henderson–Hasselbalch relation: [A−]/[HA] = 10^(pH − pKa). When pH equals pKa the ratio is 1; when pH is above pKa the base form dominates.
Does a ratio of 1 mean the buffer is neutral?
No. Ratio 1 means [A−] equals [HA] and buffer pH equals pKa. That pH may be acidic, neutral, or basic depending on the acid.
Does this return actual concentrations?
No. It returns the ratio [A−]/[HA], the pH−pKa difference, dominance, and steps. Scale the ratio to any total concentration you choose.
Is the conjugate base to acid ratio calculator free?
The browser tool is free and runs locally.
What ratio do I get when the pH is one unit above the pKa?
A ratio of 10, meaning ten parts of conjugate base for every part of acid. Each whole pH unit above the pKa multiplies the ratio by ten, and each unit below divides it by ten.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/chem/conjugate-ratio \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"ph":4.76,"pka":4.76}'const res = await fetch("https://api.kit.forhosting.com/chem/conjugate-ratio", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"ph": 4.76,
"pka": 4.76
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/chem/conjugate-ratio",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"ph": 4.76,
"pka": 4.76
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/chem/conjugate-ratio", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"ph":4.76,"pka":4.76}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"ph":4.76,"pka":4.76}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/chem/conjugate-ratio", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"ph": 4.76,
"pka": 4.76
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "chem.conjugate_ratio",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Limits
max_abs | 1000000000000 |
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
Non-numeric or missing pKa values are rejected with a clear invalid_input error so a blank cell or a text typo never silently produces a non-finite power.
How to call the API and what comes back
The absolute difference between pH and pKa must stay within three hundred so that ten to that power does not overflow double precision, and the computed ratio itself must stay at or below one trillion. Send a JSON body with two required finite numbers: ph (aliases pH, buffer_ph, buffer_pH) for the buffer pH, and pka (aliases pKa, pk_a, acid_pka) for the acid dissociation constant expressed as pKa. Absolute values must stay within the published limit of one trillion so intermediate results remain finite in IEEE double precision on the Worker and in the browser. Non-numeric strings for pka—or any value that is not a finite number—are rejected with invalid_input; the same finite-number rules apply to ph. On success the response echoes rounded ph and pH, pka and pKa, sets delta and ph_minus_pka to the same rounded difference pH minus pKa, ratio and base_to_acid to the same rounded conjugate base to acid ratio, formula to the string [A−]/[HA] equals ten to the power of pH minus pKa, dominance to base_dominant, equal, or acid_dominant, message to a short English summary, and steps to an ordered array of substitution lines. Failed validation—missing ph or pka, non-finite or non-numeric inputs, values outside absolute limits, an overflow of the exponential, or a non-positive computed ratio—returns invalid_input and is never charged. Pricing is a flat $0.002 per successful request with unit item and zero marginal unit price. Prefer sending numeric JSON rather than pre-formatted strings when you control the client; string numbers are accepted only when they match a strict finite numeric pattern including optional scientific notation.
Practical tips, limits, and related searches
When teaching, pair classic examples: acetic acid pKa about four point seven six with buffer pH equal to pKa yields ratio one; the same pKa with buffer pH one unit higher yields ratio ten (base-dominant); buffer pH one unit lower yields ratio zero point one (acid-dominant); and a non-numeric pKa string such as not-a-number demonstrates the hard invalid_input path. This landing targets people searching for a conjugate base to acid ratio calculator, buffer composition from pH and pKa, or inverse Henderson–Hasselbalch online; it is not a full titration-curve tool, not a polyprotic speciation solver, and not a pH-from-concentration converter. Failed tasks that return invalid_input do not consume prepaid balance, which keeps exploratory scripts cheap when learners deliberately send non-numeric pKa.
Integration use cases
Unit tests for chemistry helpers
Generate known-good equal, base-rich, and acid-rich ratio cases plus deliberate non-numeric pKa rejections for coding kata and grading pipelines.
Technical questions
What happens if pKa is non-numeric?
The tool returns invalid_input. pKa must be a finite number (or a string that parses as one); text like "n/a" is rejected and never charged.