Ebullioscopic constant calculator
Get a solvent's ebullioscopic constant from your own boiling-point data: a rise of 0.512 °C in a 1 mol/kg solution with a van 't Hoff factor of 1 gives Kb 0.512. Every substitution is laid out for your notes. Free in your browser.
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Run — free
Worked example
- Delta tb
- 0.512
- M
- 1
- Current (A)
- 1
- Boiling point elevation
- 0.512
- Delta t
- 0.512
- Elevation
- 0.512
- Molality
- 1
An ebullioscopic constant calculator turns measured boiling-point elevation, solution molality, and the van 't Hoff factor into the solvent constant Kb used in colligative boiling-point problems. Enter ΔTb in temperature units consistent with your tables (degrees Celsius or kelvin difference), molality m in moles of solute per kilogram of solvent, and the dimensionless factor i—one for non-electrolytes such as glucose or sucrose, about two for ideal sodium chloride, about three for ideal calcium chloride—and the tool returns Kb equals ΔTb divided by i times m, mirrored field names, a formula string, and step-by-step substitution you can paste into homework, lab notebooks, or automated tests.
What the ebullioscopic constant means for boiling-point elevation
Boiling-point elevation is the colligative property that quantifies how much the boiling temperature of a solvent rises when a non-volatile solute is dissolved. Here m is the molality in moles of solute per kilogram of solvent, i is the van 't Hoff factor that accounts for dissociation or association of the solute, and Kb is the ebullioscopic constant of the pure solvent—a characteristic temperature-per-molality scale that depends on the solvent’s molar mass, normal boiling point, and enthalpy of vaporization.
Rearranging for the solvent property gives the formula this calculator evaluates: Kb equals ΔTb divided by the product of i and m. Positive and negative ΔTb are accepted as finite numbers so signed experimental residuals can be checked, but i must stay strictly positive under the ideal colligative model.
The check path recomputes ΔTb over i times m with the same fixed rounding used for published fields, so a successful response always ships with steps you can assert in tests, lab reports, or chemistry worksheets about solvent ebullioscopic constants and colligative boiling-point elevation problems.
Practical tips, limits, and related chemistry searches
Keep temperature units consistent: if ΔTb is reported in kelvin or degrees Celsius as a difference, Kb will share that temperature unit per molal. Prefer molality over molarity for colligative work because Kb tables are defined per kilogram of solvent, not per litre of solution. Prefer sending numbers rather than pre-formatted strings when you control the client; string numbers are accepted only when they match a strict finite numeric pattern.
Prefer this capability when you already have ΔTb, molality, and i and only need Kb; if your goal is to predict elevation from a known table Kb, invert the same formula offline or use a dedicated elevation solver. Round-trip checks are easy: recompute ΔTb divided by i times m by hand and confirm it equals the published kb within the same twelve-decimal rounding, and confirm that kb times i times m recovers the original elevation within that rounding.
What you can do with it
Chemistry homework checks for Kb = ΔTb/(i·m)
Students enter boiling-point elevation, molality, and van 't Hoff factor from textbook colligative-property problems and compare hand-written Kb against a deterministic result before submitting.
Lab recovery of solvent Kb from measured elevation
Quickly convert bench ΔTb and prepared molality into an effective solvent ebullioscopic constant under the ideal i·m model for lab reports.
FAQ
What is the ebullioscopic constant Kb?
Kb is the solvent-specific factor in the ideal colligative equation ΔTb = i·Kb·m. Rearranged, Kb = ΔTb/(i·m). Units are typically °C·kg/mol or K·kg/mol.
What happens when molality is zero?
Kb is undefined because you would divide by zero.
What van 't Hoff factor should I use?
Ideal strong electrolytes use the number of ions (NaCl ≈ 2, CaCl₂ ≈ 3). Real solutions may use an effective i less than the ideal ion count.
Does this look up Kb for named solvents?
No. It recovers Kb from your measured or textbook ΔTb, molality, and i. Use a solvent data table if you need literature values by name.
Is the ebullioscopic constant calculator free?
The browser tool is free and runs locally.
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/ebullioscopic-constant \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"delta_tb":0.512,"m":1,"i":1}'const res = await fetch("https://api.kit.forhosting.com/chem/ebullioscopic-constant", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"delta_tb": 0.512,
"m": 1,
"i": 1
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/chem/ebullioscopic-constant",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"delta_tb": 0.512,
"m": 1,
"i": 1
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/chem/ebullioscopic-constant", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"delta_tb":0.512,"m":1,"i":1}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"delta_tb":0.512,"m":1,"i":1}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/chem/ebullioscopic-constant", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"delta_tb": 0.512,
"m": 1,
"i": 1
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "chem.ebullioscopic_constant",
"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
Zero molality is rejected with a clear invalid_input error because dividing by i times zero is undefined; non-positive van 't Hoff factors are also rejected so the model never invents a non-physical constant.
What the ebullioscopic constant means for boiling-point elevation
In the ideal dilute limit used in introductory physical chemistry, the elevation is proportional to the effective particle molality: ΔTb equals i times Kb times m. Teachers and automated graders care about the zero-molality rejection as much as the success path: a learner who forgets to convert grams of solvent into kilograms, or who leaves molality at zero after a failed dilution calculation, should see an explicit invalid_input message instead of Infinity or NaN.
How to call the API and what comes back
Molality m must be non-zero; values whose absolute value is at or below one times ten to the minus fifteen are treated as zero and rejected. The van 't Hoff factor i must be strictly positive. Send a JSON body with three required finite numbers: delta_tb (aliases boiling_point_elevation, delta_t, dtb, elevation, deltaTb, DeltaTb, and dTb), m (aliases molality, molal, and m_solute), and i (aliases van_t_hoff, vant_hoff, vanthoff, factor, and i_factor). Absolute values must stay within the published limit of one trillion so intermediate products remain finite in IEEE double precision on the Worker and in the browser. On success the response echoes rounded delta_tb, m, and i, mirrors them as boiling_point_elevation, molality, van_t_hoff, and related aliases, sets kb, ebullioscopic_constant, and Kb to the same rounded constant, formula to the string Kb equals ΔTb over i times m, equation to a filled substitution string, message to a short English summary, and steps to an ordered array of calculation lines including the denominator product i times m. Failed validation—missing fields, non-finite numbers, values outside absolute limits, zero molality, or non-positive i—returns invalid_input and is never charged. Pricing is a flat $0.002 per successful request with unit item and zero marginal unit price.
Practical tips, limits, and related chemistry searches
When teaching chemistry, pair examples: water-like ΔTb equals zero point five one two with m equals one and i equals one recovers Kb about zero point five one two kelvin per molal; a one-molal ideal sodium chloride case with i equals two halves the recovered Kb for the same elevation; a dilute organic non-electrolyte with i equals one and small elevation scales linearly; and deliberately send m equals zero to demonstrate the hard invalid_input path that guards against undefined division. This landing targets people searching for an ebullioscopic constant calculator, Kb from boiling-point elevation, or solvent colligative constant homework help online; it is not a freezing-point depression or cryoscopic-constant tool, not a full multi-component Raoult’s-law boiling calculator, and not a tabulated solvent lookup by name. Failed tasks that return invalid_input do not consume prepaid balance, which keeps exploratory scripts cheap when learners deliberately send zero molality.
Integration use cases
Unit tests for student colligative solvers
Generate known-good ebullioscopic constant cases plus deliberate zero-molality rejections for coding kata expected values in chemistry tools.