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What is the freezing point of an aqueous solution that boils at 103.7 degrees Celsius?

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Final answer:

The freezing point of an aqueous solution that boils at 103.7°C is expected to be -3.7°C. This estimation assumes the proportionality between freezing point depression and boiling point elevation, tolerating the solution to be appropriately dilute.

Step-by-step explanation:

The freezing point of an aqueous solution can be determined by understanding the relationship between boiling and freezing points of solutions compared to their pure solvent counterparts. The normal freezing point of water is 0.0°C, which is lowered when a solute is dissolved, due to the freezing point depression. Similarly, the normal boiling point, 100°C, increases due to the boiling point elevation. These changes in physical properties are dependent on the amount of solute present as well as its nature.

Given the solution boils at 103.7°C, which is 3.7°C above the normal boiling point of water, and assuming the solution is not super concentrated to negate the equation for boiling point elevation (Equation 11.5.5), we would expect an equivalent freezing point depression. Since freezing point depression is proportional to boiling point elevation, we can infer a similar magnitude of change in the opposite direction for the freezing point. Hence, decreasing the normal freezing point of water by 3.7°C yields a freezing point of -3.7°C for this solution.

User Rhonie
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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
User Dmreshet
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