Molality

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Molality is the measure as the number of moles  of a solute in a kilogram of solvent.

The equation for molality is:

molality (m) = moles of solute (mol)

                          mass of solvent (kg)

Example Problem:

What is the molal concentration of a solution when you have 2.5 g of NaCl in 4 kg of water?

 First change 2.5g of NaCl into mole of NaCl

find the molar mass of NaCl

Na= 22.99 g/mol

Cl= 35.45g/mol

+_____________

    58.44 g/mol for NaCl

then find how much of a mole is 2.5 g of NaCl make

2.5g NaCl  X  1mol NaCl      = 0.043 mol NaCl

                      58.44 g NaCl

Now your ready to find the molality

molality (m) = 0.043 mol NaCl

                             4.00 kg H₂O

                    = 0.011 m NaCl