For this, we use equations from the colligative properties of solutions specifically boiling point elevation and freezing point depression. The equations for these are expressed as:
ΔTb = kb m
where k is a boiling point elevation constant and m is the concentration in terms of molality
ΔTf = kf m
where k is a freezing point elevation constant and m is the concentration in terms of molality
We use both expression to solve for the freezing point. For this case, concentration is the same. The equation will then be:
ΔTf = kf ( ΔTb / kb )
0-Tf = 1.86 (103.7 - 100 / 0.512 )
Tf = -13.4°C
