The rule to calculate molality is as follows:
molality = number of moles of solute / kg of solvent
From the givens:
number of moles of solute (CaBr2) = 2.5 moles
Kg of solvent (water) = 5 kg
Substituting by these givens in the above mentioned equation, we can calculate molality as follows:
molality = 2.5 / 5 = 0.5 m
