Sales Toll Free No: 1-855-666-7446

Molality Calculator

Top
Estimating the concentration of a solution is known as Molality. The number of moles of solute dissolved in solvent of mass one kilogram. Molality is denoted by "M".

Molality is calculated by the formula given,
Molality M = $\frac{number\ of\ moles\ of\ solute}{weight\ of\ solvent\ in\ kilogram}$

By taking the mass of solute, the number of moles is calculated and is divided by the mass of solvent to get the molality of the solution. Plug in the required values into this online Molality calculator and get the Molality for the given solution.
 

Steps

Back to Top
Step 1: Note down the given values of the problem.

Step 2: Find the moles of solute from its mass i.e.,
n = $\frac{mass\ of\ solute}{molecular\ mass\ of\ solute}$

Step 3: Substitute those values into the molality formula given to get the molality of the solution.

Problems

Back to Top
Given below are some of the problems to understand the concept and calculate the molality of solution.

Solved Examples

Question 1: If NaCl of 6g is dissolved in 25 g of water, determine the molality of the solution. 
Solution:
 
Step 1: Given :
mass of solvent = 25 g
mass of solute = 6 g

Step 2: moles of solute,  n = $\frac{mass\ of\ solute}{molecular\ mass\ of\ solute}$

molecular mass = 22.99 + 35.45 = 58.44 g/mol 

n = $\frac{6 g}{58.44 g/mol}$ = 0.102 mol

Step 3: Molality M = $\frac{number\ of\ moles\ of\ solute}{mass\ of\ solvent\ in\ kilogram}$

Molality M = $\frac{0.102\ mol}{25 \times 10^{-3}\ kg}$

Molality M = 4.08 m.

Therefore, molality of solution is 4.08 m.
 

Question 2: What is the mass of water present in 2.5 m solution which contains 5 g of NaCl?
Solution:
 
Step 1: Given :
molality of solution = 2.5 m
mass of solute = 5 g

Step 2: moles of solute,  n = $\frac{mass\ of\ solute}{molecular\ mass\ of\ solute}$

molecular mass = 22.99 + 35.45 = 58.44 g/mol

n = $\frac{5 g}{58.44 g/mol}$ =  0.086 mol

Step 3: Molality M = $\frac{number\ of\ moles\ of\ solute}{mass\ of\ solvent\ in\ kilogram}$

mass of solvent = $\frac{number\ of\ moles\ of\ solute}{Molality\ M}$

mass of solvent = $\frac{0.086\ mol}{2.5\ m}$

mass of solvent = 0.0344 kg

Therefore, the mass of solvent is 0.0344 kg.