# Boiling Point Elevation Calculator

Calculate boiling point elevation with ΔTb = iKbm. Supports water, ethanol, benzene, and custom solvents. Free colligative property calculator.

## What this calculates

Calculate how much the boiling point of a solvent increases when a solute is dissolved in it. Uses the colligative property formula ΔTb = i × Kb × m, where i is the van't Hoff factor, Kb is the ebullioscopic constant, and m is molality.

## Inputs

- **Van't Hoff Factor (i)** — min 1, max 10 — Number of particles the solute dissociates into (1 for non-electrolytes, 2 for NaCl, 3 for CaCl₂).
- **Molality (m)** (mol/kg) — min 0 — Moles of solute per kilogram of solvent.
- **Solvent** — options: Water (Kb = 0.512 °C/m, BP = 100 °C), Ethanol (Kb = 1.22 °C/m, BP = 78.37 °C), Benzene (Kb = 2.53 °C/m, BP = 80.1 °C), Custom solvent — Select a solvent or choose custom to enter your own Kb value.
- **Custom Kb** (°C/m) — min 0 — Ebullioscopic constant of the solvent. Only used when 'Custom solvent' is selected.
- **Custom Normal Boiling Point** (°C) — Normal boiling point of the pure solvent in °C. Only used when 'Custom solvent' is selected.

## Outputs

- **ΔTb (Elevation)** (°C) — The boiling point elevation in degrees Celsius.
- **New Boiling Point** (°C) — The new boiling point of the solution.
- **Explanation** — formatted as text — Step-by-step calculation breakdown.

## Details

Boiling point elevation is a colligative property, meaning it depends on the number of solute particles in solution, not their identity. When a non-volatile solute is dissolved in a solvent, the boiling point of the solution is higher than that of the pure solvent.

The Formula: ΔTb = i × Kb × m

- i = van't Hoff factor (number of particles per formula unit). For non-electrolytes like sugar, i = 1. For NaCl, i = 2 (Na⁺ + Cl⁻). For CaCl₂, i = 3.

- Kb = ebullioscopic constant, a property of the solvent. Water has Kb = 0.512 °C·kg/mol.

- m = molality, moles of solute per kilogram of solvent.

Why It Happens

Adding solute lowers the vapor pressure of the solvent (Raoult's law). Since the liquid must reach a higher temperature to achieve a vapor pressure equal to atmospheric pressure, the boiling point increases. The elevation is directly proportional to the concentration of solute particles.

Practical Applications

Antifreeze mixtures (ethylene glycol in water) raise the boiling point and lower the freezing point of engine coolant. Cooking with salted water results in a slightly higher boiling point, though the effect is small at typical cooking concentrations.

## Frequently Asked Questions

**Q: What is the van't Hoff factor?**

A: The van't Hoff factor (i) represents the number of particles a solute produces when dissolved. Non-electrolytes (like glucose) have i = 1. Strong electrolytes dissociate completely: NaCl has i = 2 (Na⁺ + Cl⁻), CaCl₂ has i = 3 (Ca²⁺ + 2Cl⁻). Weak electrolytes have i values between 1 and their maximum dissociation.

**Q: Why does boiling point elevation depend on particle count, not identity?**

A: Boiling point elevation is a colligative property, determined only by the number of dissolved particles. The solute particles reduce the mole fraction of the solvent at the surface, lowering vapor pressure. The solvent must be heated more to reach the vapor pressure needed for boiling.

**Q: How much does salt raise the boiling point of water?**

A: Adding 1 mole of NaCl (58.4 g) per kilogram of water raises the boiling point by about 1.024 °C (0.512 × 2 × 1). A typical cooking amount of salt (1 tablespoon, about 18 g per liter) raises the boiling point by less than 0.2 °C — barely noticeable.

**Q: What is the difference between boiling point elevation and freezing point depression?**

A: Both are colligative properties caused by dissolved solute particles. Boiling point elevation raises the temperature needed to boil, while freezing point depression lowers the temperature at which the solution freezes. They use similar formulas but with different constants (Kb vs Kf).

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Source: https://vastcalc.com/calculators/chemistry/boiling-point-elevation
Category: Chemistry
Last updated: 2026-04-21