ForHosting KIT · Science

Solution freezing point calculator

Water with Kf of 1.86 and a 1 mol/kg non-electrolyte freezes at −1.86 °C instead of 0 °C. Enter the solvent's freezing point, molality, Kf and particle factor to see both the drop and the new freezing temperature, with each substitution shown. Free in your browser.

  • Free
  • Runs in your browser
  • No sign-up
  • Your data stays on your device
Run — free How it works & API
Use it from WebAPIEmailTelegramApp soon

Run — free

Worked example

If you enter
Tf solvent
0
M
1
Cryoscopic
1.86
Current (A)
1
You get
Solvent freezing point
0
Tf0
0
Molality
1
Cryoscopic constant
1.86

A solution freezing point calculator turns the pure solvent freezing temperature, solution molality, cryoscopic constant, and van 't Hoff factor into the depressed freezing temperature of the mixture. Enter Tf° for the pure solvent (zero degrees Celsius for water under standard conditions, or your tabulated solvent value), molality m in moles of solute per kilogram of solvent, the solvent cryoscopic constant Kf in temperature units per molal, 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 ΔTf equals i times Kf times m, the solution freezing point Tf equals Tf° minus ΔTf, mirrored field names, formula strings, and step-by-step substitution you can paste into homework, lab notebooks, or automated tests.

What freezing-point depression means for colligative solutions

Freezing-point depression is the colligative property that quantifies how much the freezing temperature of a solvent falls 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 Kf is the cryoscopic constant of the pure solvent—a characteristic temperature-per-molality scale that depends on the solvent’s molar mass, normal freezing point, and enthalpy of fusion.

Once you know ΔTf, the solution freezing point follows immediately: Tf equals Tf° minus ΔTf, where Tf° is the freezing temperature of the pure solvent in the same temperature unit. Zero molality is allowed and simply recovers Tf equals Tf° with ΔTf equal to zero, which is a useful limit check for worksheets.

The check path recomputes i times Kf times m and subtracts from Tf° 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 freezing-point depression and cryoscopic constants.

Practical tips, limits, and related chemistry searches

Keep temperature units consistent: if Tf° is in degrees Celsius and Kf is in °C·kg/mol, ΔTf and Tf share that Celsius scale; the same rule applies when you work entirely in kelvin with a kelvin-based Kf. Prefer molality over molarity for colligative work because cryoscopic 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 Tf°, m, Kf, and i and only need the depressed freezing temperature; if your goal is to recover Kf from a measured depression, invert the colligative formula offline. Round-trip checks are easy: recompute i times Kf times m by hand, subtract from Tf°, and confirm both ΔTf and Tf match the published fields within the same twelve-decimal rounding.

What you can do with it

Chemistry homework checks for Tf = Tf° − i·Kf·m

Students enter solvent freezing point, molality, cryoscopic constant, and van 't Hoff factor from textbook colligative-property problems and compare hand-written Tf against a deterministic result before submitting.

Lab prediction of antifreeze and brine freezing points

Quickly convert prepared molality and tabulated Kf into an expected solution freezing temperature under the ideal i·m model for lab reports and process checks.

FAQ

How is the solution freezing point calculated?

Under the ideal colligative model, ΔTf = i·Kf·m and Tf = Tf° − ΔTf, where Tf° is the pure solvent freezing point, m is molality, Kf is the cryoscopic constant, and i is the van 't Hoff factor.

What happens when molality is negative?

Negative molality is not physical for this model.

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 Kf for named solvents?

No. You supply Kf (and Tf°) from your table or lab data. Common water values are Tf° = 0 °C and Kf ≈ 1.86 °C·kg/mol, but the calculator does not hard-code solvents.

Is the solution freezing point calculator free?

The browser tool is free and runs locally.

Related tools

Ebullioscopic constant calculatorScienceOsmotic pressure calculatorScienceVapor pressure lowering calculatorScienceCalorimeter constant calculatorScienceWater potential calculatorScienceMole fraction to molality calculatorScienceIdeal gas law chemistry calculatorScienceMolality calculatorScience

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

POSThttps://api.kit.forhosting.com/chem/solution-freezing-point

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/solution-freezing-point \
  -H "Authorization: Bearer $KIT_KEY" \
  -H "Content-Type: application/json" \
  -d '{"tf_solvent":0,"m":1,"kf":1.86,"i":1}'

Example request

{
  "tf_solvent": 0,
  "m": 1,
  "kf": 1.86,
  "i": 1
}

Example response

{
  "task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
  "type": "chem.solution_freezing_point",
  "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

Per request$0.002

Published price — no tokens, no invented credits. A failed task is never charged.

Limits

max_abs1000000000000

Errors

HTTPCodeMeaning
401unauthorizedMissing or invalid API key.
402insufficient_balanceYour balance doesn't cover the task price.
404unknown_typeThat task type doesn't exist.
429rate_limitedToo many requests. Use the webhook instead of polling.

Technical notes

Negative molality is rejected with a clear invalid_input error because a negative particle concentration is not physical under the ideal colligative model.

What freezing-point depression means for colligative solutions

In the ideal dilute limit used in introductory physical chemistry, the depression is proportional to the effective particle molality: ΔTf equals i times Kf times m. Teachers and automated graders care about the negative-molality rejection as much as the success path: a learner who swaps mass of solvent and mass of solute, or who accidentally types a minus sign on molality after a unit conversion, should see an explicit invalid_input message instead of a non-physical elevation of the freezing point.

How to call the API and what comes back

Molality m must not be negative; any strictly negative value is rejected. Send a JSON body with four required finite numbers: tf_solvent (aliases solvent_freezing_point, tf0, Tf0, freezing_point_solvent, t_f_solvent, and tf_pure), m (aliases molality, molal, and m_solute), kf (aliases cryoscopic_constant, Kf, freezing_point_constant, k_f, and kf_solvent), 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 tf_solvent, m, kf, and i, mirrors them under common aliases, sets delta_tf, freezing_point_depression, and DeltaTf to the same rounded depression, sets tf_solution, solution_freezing_point, and freezing_point to the same rounded solution temperature, formula to the string Tf equals Tf° minus i times Kf times m, formula_delta to ΔTf equals i times Kf times m, equation to a filled substitution string, message to a short English summary, and steps to an ordered array of calculation lines. Failed validation—missing fields, non-finite numbers, values outside absolute limits, or negative molality—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 at Tf° equals zero with Kf about one point eight six, m equals one, and i equals one recovers ΔTf about one point eight six and Tf about minus one point eight six; a one-molal ideal sodium chloride case with i equals two roughly doubles the depression; zero molality recovers the pure solvent freezing point; and deliberately send a negative molality to demonstrate the hard invalid_input path that guards against non-physical concentration. This landing targets people searching for a solution freezing point calculator, freezing-point depression from molality, or cryoscopic constant homework help online; it is not an ebullioscopic boiling-point elevation tool, not a solvent lookup by name, and not a full multi-component solid–liquid phase diagram solver. Failed tasks that return invalid_input do not consume prepaid balance, which keeps exploratory scripts cheap when learners deliberately send negative molality.

Integration use cases

Unit tests for student freezing-point solvers

Generate known-good depression cases plus deliberate negative-molality rejections for coding kata expected values in chemistry tools.

Read the full KIT documentation →