Molality Calculator
Calculate molality (mol/kg), convert between molarity and molality, and determine solution concentrations
Calculate Molality
Amount of dissolved substance in moles
Mass of the solvent (usually water)
Current Calculation
Mode: Basic (using known moles)
Moles of solute: 0 mol
Solvent mass: 0.000 kg
Calculation Results
Additional Information
Calculation Details
Formula: Molality = moles of solute / mass of solvent (kg)
Calculation: 0 mol ÷ 0.000 kg = 0.0000 mol/kg
Unit: mol/kg (molal) - independent of temperature
Application:
Concentration Analysis
Example Calculation
Sodium Chloride Solution
Question: What is the molality of a solution containing 70.128 g of NaCl dissolved in 1.5 kg of water?
Given: Mass of NaCl = 70.128 g, Mass of water = 1.5 kg
Find: Molality of the solution
Molar mass of NaCl: 58.44 g/mol (Na = 22.99 + Cl = 35.45)
Step-by-Step Solution
Step 1: Calculate moles of NaCl
Moles = 70.128 g ÷ 58.44 g/mol = 1.2 mol
Step 2: Apply molality formula
Molality = moles of solute ÷ mass of solvent (kg)
Step 3: Calculate molality
Molality = 1.2 mol ÷ 1.5 kg = 0.8 mol/kg
Answer: The molality is 0.8 molal (0.8 mol/kg)
Molarity vs Molality
Molarity (M)
mol/L - Temperature dependent
Based on solution volume
Molality (m)
mol/kg - Temperature independent
Based on solvent mass
Use Molarity: Laboratory work, easier to measure
Use Molality: Precise calculations, temperature studies
Conversion Formulas
Molality Formula
m = n / kg_solvent
moles ÷ kilograms of solvent
Molarity to Molality
m = M/(d - M×W)
d = density, W = molar mass
Molality to Molarity
M = m×d/(1 + m×W)
Requires solution density
Common Solvents
Understanding Molality
What is Molality?
Molality is a measure of solution concentration defined as the number of moles of solute per kilogram of solvent. Unlike molarity, molality is independent of temperature because it's based on mass rather than volume.
When to Use Molality?
- •Colligative property calculations (freezing point, boiling point)
- •Temperature-sensitive experiments and reactions
- •Precise analytical chemistry measurements
- •Thermodynamic calculations and studies
Advantages of Molality
Temperature Independent
Mass doesn't change with temperature
Volume-based units expand/contract
High Precision
Mass measurements are very accurate
Suitable for analytical work
Colligative Properties
Essential for phase change calculations
Freezing/boiling point determination