Freezing Point Depression Lab

I. LIQUID - Identification of an Unknown Liquid: Using the physical properties of Solubility, Density, and Boiling Point.

The sugar molecules don’t fit into this, so when you freeze the water, the water freezes first and the sugar stays behind in the liquid part as the ice develops. Sugar makes the ice harder to form, therefore lowering the freezing point. By lowering the freezing point, it keeps the ice from re-freezing as easily, helping to melt the rest of the ice.

Other substances that dissolve in water also lower the freezing point of the solution. The amount by which the freezing point is lowered depends only on the number of molecules dissolved, not on their chemical nature. This is an example of a colligative property. In this project, you'll investigate different substances to see how they affect the rate at which ice cubes melt. You'll test substances that dissolve in water (i.e., soluble substances), like salt and sugar, as well as substances that don't dissolve in water (i.e., insoluble substances), like sand and pepper. Which substances will speed up the melting of the ice?

The freezing point constant (Kf) of water is 1.86 °C m-1. Each mass amount and Van’t Hoff factor was calculated then analyzed in a table.

In order to fulfil the labs purpose, the lab was split into two parts. The first part consisted of measuring and determining the freezing point depression of the solution water. The second part consisted of measuring and determining the freezing point depression of a solution that consisted of water and an unknown solute.

The freezing point depression constant for water that was experimentally determined in this analysis was 0.0479 °C/m, which was derived from the slope of the trend line in Figure 4. This is significantly lower than the constant stated in the literature of 1.86 °C/m.1 The freezing point temperature determined via cryoscopy should have been much lower in the high sucrose concentration solutions.

The objectives in this laboratory were to be able to calculate the freezing point depression among three trials of unknowns, be able to correctly measure the freezing points of p-xylene, and to be able to calculate the molar masses of the unknowns by found freezing point depression values. This was done to be able to understand and apply a concept names supercooling. Supercooling is when a liquid is put far under its original freezing point and remains a liquid or gas. This happens when a substance is cooled so quickly that it’s easier for it to stay a liquid than to crystalize, until it reached its nucleation point and begins to heat up returning to its freezing point (image 4). The supercooling of p-xylene was observed in three

2) When water freezes there are additional hydrogens bonds formed between molecules and those molecules become slow.

Purpose: The purpose of this laboratory was to gain an understanding of the differences between the freezing points of pure solvent to that of a solvent in a solution with a nonvolatile solute, and to compare the two.

In salt, there are more particles in 10 grams of sodium chloride (salt) than in 10 grams of sucrose (sugar). When there are more particles, melting will occur faster. When there is one type of molecule, say water, it is easier for the molecules to get in an orderly manner to become solid water, or ice. When other types of molecules are added, the water molecules lose their order and it becomes harder to be frozen. Therefore, when there are more particles of a different type, then the freezing point will become lower.

The most common example of freezing point depression is in the salting of roads when it snows (Kimbrough, 2006). As the melting of the first flakes on the warm road occurs, a solution of salty water is created which has a lower freezing point than pure snow (Kimbrough, 2006). Now, the temperature will not get cold enough to freeze the salty solution the way it can freeze water, keeping ice and snow from bonding to the pavement (Kimbrough, 2006). In this lab, the freezing point depression was calculated experimentally by adding an unknown solute to Lauric Acid,

-The salt lowers the freezing point of the ice. 3: Why is the salt-ice mixture needed to freeze the ice cream mixture? -The ice and salt takes heat from the milk mixture which is why the ice melts and the milk freezes. 4: Discuss the reason for the heat transfer that occurs as the ice melts and the ice cream mixture freezes.

In the textbook is states that the vapor pressure is the pressure caused by molecules in the gas phase that are in a equilibrium. When salt is added to ice the salt is a nonvolatile solute is because the vapor pressure to lower. Because of the vapor pressure is lowered it lowers the freezing point of

However, since the mixture is not just pure water, which freezes at 0° Celsius, the freezing point must be cooler. Freezing point depression is a colligative property where more solute is added to the solvent. In this case, salt is the solute and the ice/water is the solvent. If the concentration of the solution is increased, consequently, the freezing point will decrease to be lower than that of the usual. The new change will then allow the ice to absorb the heat and melt, while transferring the coldness to the ice cream.

The specific property observed in this lab was the freezing point depression caused by the additives. This is the change in the freezing point between a standard solvent and said solvent with added solutes. This changes the entropy of the system, making the properties change somewhat, lowering the freezing point itself with the addition of more solute. Hence, the term ‘freezing point depression’.