# Colligative Properties, Freezing Point Depression - Chemistry Lab

• jallison
In summary, we discussed the effects of incomplete dissolution and supercooling on freezing point depression and calculated molar mass of unknown compounds in a solution. We also calculated the percent ionization of a weak monoportic acid in an aqueous solution.
jallison
Colligative Properties, Freezing Point Depression -- Chemistry Lab

## Homework Statement

In an attempt to hurry the experiment along a student did not completely dissolve the unknown nonelectrolyte. Will the freezing point depression of the solution be larger, unaffected, or smaller compared to if the compound was dissolved completely? Will the calculate molar mass be of the unknown be larger, unaffected, or smaller compared to if the compound was dissolved completely?

A lazy student neglected to stir the contents of the test tube when attempting to freeze the solution of the unknown electrolyte. This allowed the solution to undergo supercooling. Will the freezing point depression of the solution be larger, unaffected, or smaller compared to a properly stirred solution?Will the calculated molar mass of the unknown be be larger, unaffected, or smaller compared to a properly stirred solution?

The van't Hoff i factor for an aqueous solution of a weak monoportic acid was measured as 1.26. What is the percent ionization of this acid in the solution?

## Homework Equations

ΔTfp= imK(fp)
where ΔTfp is the change in the freezing point, i is the van't Hoff's factor (number of particles) and k is the freezing point depression of solute

molar mass = (g solute/kg solvent)/ΔTfp/iKfp

## The Attempt at a Solution

I am really not sure. Any help would be appreciated.

For the first question, if the compound was not dissolved completely, the freezing point depression would be smaller. The calculated molar mass of the unknown would also be smaller. For the second question, if the solution was allowed to undergo supercooling, the freezing point depression would be larger. The calculated molar mass would also be larger. For the third question, the percent ionization of this acid in the solution can be calculated using the following equation: Percent Ionization = (i - 1) / i x 100. In this case, the percent ionization would be 26%.

## 1. What are colligative properties?

Colligative properties are physical properties of a solution that depend on the concentration of solute particles, rather than the identity of the solute. These properties include boiling point elevation, freezing point depression, vapor pressure lowering, and osmotic pressure.

## 2. How does adding a solute affect the freezing point of a solution?

Adding a solute to a solvent decreases the freezing point of the solution. This is because the presence of solute particles disrupts the formation of crystal lattices, making it more difficult for the solvent molecules to arrange themselves in a regular pattern and freeze.

## 3. What is freezing point depression and how is it measured?

Freezing point depression is the phenomenon where the freezing point of a solution is lower than the freezing point of the pure solvent. It is measured by taking the difference between the freezing point of the pure solvent and the freezing point of the solution.

## 4. How are colligative properties useful in real-life situations?

Colligative properties have many practical applications, such as in antifreeze solutions for cars, where the addition of solutes lowers the freezing point of the solution and prevents the engine from freezing in cold temperatures. They are also important in the food industry, where adding salt or sugar to food products can lower the freezing point and prevent them from freezing at certain temperatures.

## 5. Can colligative properties be used to determine the molecular weight of a solute?

Yes, colligative properties, specifically freezing point depression, can be used to determine the molecular weight of a solute. By measuring the change in freezing point and using equations such as the van't Hoff equation, the molecular weight of the solute can be calculated. This is the basis for many molecular weight determination methods in chemistry labs.

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