The freezing point of pure water can be determined using the freezing point depression equation, which is given by the formula:
ΔTf = Kf × m
Where:
- ΔTf = change in freezing point
- Kf = freezing point depression constant of the solvent (for water, it is typically 1.86°C kg/mol)
- m = molality of the solution
To find the freezing point of pure water, you start by understanding that the freezing point of pure water is 0°C. When a solute is added, the freezing point is depressed (lowered) based on the concentration of the solute in the solution. Therefore, if you know the amount and type of solute you are adding, you can calculate the molality (m) of your solution.
For example, if you dissolve a known amount of solute in a certain mass of water, you will first calculate the molality. Once you have this value, you can apply it in the freezing point depression equation to find ΔTf.
Once you calculate ΔTf, you subtract this value from the original freezing point of pure water (0°C) to determine the new freezing point of your solution:
New Freezing Point = 0°C – ΔTf
So, the freezing point of pure water is always 0°C, but when you add a solute, you can use this equation to find out how much lower the freezing point will be due to the solute you added.