How do you calculate molality from molarity?
1 Answer
See explanation.
Explanation:
If all you are given is Molarity, then you also need to know the density of the solution to calculate molality, m (mol/kg solvent).
The easiest way to understand the process is to assume you have 1L of solution which is 1000 mL. Think of the units of molarity and molality. So here is an example:
What is the molality of a
We know that in
If we figure out how many kg of water there are in
First let's figure out the mass of the solution using dimensional analysis and density:
? g soln=1.00L×1000mL1L×1.12 g1mL=1120 g solution
Now we need to know the mass of just the water.
? g water=mass of the solution−mass of NaCl in the solution
=1120 g soln−(3.00mol NaCl×58.4 g1 mol NaCl)
=1120 g soln−175 g NaCl=945 g water
=0.945 kg of water
Now, use the units of molality as an equation:
molality(mol solutekg solvent)=no. moles NaClno. kg water
So,
molality=3.00 mol NaCl0.945 kg water=3.17 m NaCl