Molality Calculator

Calculate the molality (mol/kg) of a solution quickly and accurately.

Enter the required values for solute and solvent to determine the molality of your solution. You can provide either the number of moles of solute or its mass and molar mass.

Examples

See how to calculate molality in real scenarios:

Sodium Chloride in Water

Basic Example

Calculate the molality when 0.5 mol NaCl is dissolved in 1 kg water.

Moles of Solute (n): 0.5 mol

Solute Mass (g): g

Solute Molar Mass (g/mol): g/mol

Solvent Mass: 1 kg

Solvent Mass Unit: kg

Glucose Solution

Mass and Molar Mass

Find the molality when 18 g glucose (molar mass 180 g/mol) is dissolved in 500 g water.

Moles of Solute (n): mol

Solute Mass (g): 18 g

Solute Molar Mass (g/mol): 180 g/mol

Solvent Mass: 500 g

Solvent Mass Unit: g

Ethanol in Small Amount of Water

Small Solvent Amount

Calculate the molality when 0.2 mol ethanol is dissolved in 200 g water.

Moles of Solute (n): 0.2 mol

Solute Mass (g): g

Solute Molar Mass (g/mol): g/mol

Solvent Mass: 200 g

Solvent Mass Unit: g

Potassium Nitrate Solution

Mass and Molar Mass (kg)

Find the molality when 10 g KNO3 (molar mass 101.1 g/mol) is dissolved in 2 kg water.

Moles of Solute (n): mol

Solute Mass (g): 10 g

Solute Molar Mass (g/mol): 101.1 g/mol

Solvent Mass: 2 kg

Solvent Mass Unit: kg

Other Titles
Understanding Molality Calculator: A Comprehensive Guide
Everything you need to know about calculating solution molality.

What is Molality?

  • Definition of Molality
  • Difference Between Molality and Molarity
  • Importance in Chemistry
Molality is a measure of the concentration of a solute in a solution, defined as the number of moles of solute per kilogram of solvent. It is a key concept in chemistry, especially when temperature changes are involved, as molality does not change with temperature.
Molality vs. Molarity

Molality in Practice

  • A solution with 1 mol of NaCl in 1 kg of water has a molality of 1 mol/kg.
  • Molality remains constant even if the solution's volume changes due to temperature.

Step-by-Step Guide to Using the Molality Calculator

  • Input Requirements
  • Calculation Process
  • Interpreting Results
To use the Molality Calculator, enter either the number of moles of solute or provide the solute's mass and molar mass. Then, input the mass of the solvent and select the appropriate unit. The calculator will compute the molality instantly.
How to Enter Data

Input Scenarios

  • If you know the moles of solute, enter it directly.
  • If you only know the mass and molar mass, the calculator will compute moles for you.

Real-World Applications of Molality

  • Laboratory Solution Preparation
  • Industrial Chemistry
  • Academic Research
Molality is widely used in laboratory and industrial settings to prepare solutions with precise concentrations. It is also essential in research where temperature stability is crucial.
Why Use Molality?

Applications

  • Preparing a freezing point depression experiment.
  • Calculating solution concentration for chemical reactions.

Common Misconceptions and Correct Methods

  • Molality vs. Molarity Confusion
  • Unit Conversion Errors
  • Incorrect Solute/Solvent Identification
A common mistake is confusing molality with molarity. Remember, molality is based on solvent mass, not solution volume. Always ensure correct unit conversions and identify solute and solvent properly.
Avoiding Calculation Mistakes

Tips

  • Do not use total solution mass for molality.
  • Always convert solvent mass to kilograms.

Mathematical Derivation and Examples

  • Molality Formula
  • Sample Calculations
  • Advanced Scenarios
Molality (b) is calculated as the number of moles of solute divided by the mass of solvent in kilograms. If you have solute mass and molar mass, first calculate moles, then divide by solvent mass in kg.
Formula: b = n / m (kg)

Worked Examples

  • 10 g NaCl (molar mass 58.44 g/mol) in 500 g water: n = 10/58.44 = 0.171 mol; m = 0.5 kg; b = 0.171/0.5 = 0.342 mol/kg.
  • 0.2 mol glucose in 200 g water: m = 0.2/0.2 = 1 mol/kg.