# What is the molality of a solution of 10 g NaOH in 500 g water?

molality = $\left(\text{moles of [solute](http://socratic.org/chemistry/solutions-and-their-behavior/solute)")/("kilograms of [solvent](http://socratic.org/chemistry/solutions-and-their-behavior/solvent)}\right)$
moles of NaOH = 10 g NaOH × $\left(1 \text{mol NaOH")/(40.00"g NaOH}\right)$ = 0.25 mol NaOH
kilograms of H₂O = 500 g H₂O × $\left(1 \text{kg H₂O")/(1000"g H₂O}\right)$ = 0.500 kg H₂O
molality = $\left(\text{moles of solute")/("kilograms of solvent") = (0.25"mol")/(0.500"kg}\right)$ = 0.50 mol/kg