Colligative Properties Freezing Point Depression And Molar Mass
Experiment 3
Colligative Properties
Freezing-Point Depression and Molar Mass
By,
Andrew Klingsporn
Joby J.
Chem 212
Dr. Chandana Meegoda
2/11/2009
Purpose The purpose of this experiment is to determine the Molar Mass of an unknown substance using its freezing point depression.
Introduction
There are two types of mixtures; homogenous and heterogeneous. Homogenous mixtures have components that are uniformly mixed, while heterogeneous mixtures do not. A solution is a homogenous mixture that has two or more substances. A solution is mainly made of a solvent, while the solute is the smaller part of the solution.
A solution’s freezing point depression is a type of colligative property. There are four types of colligative properties: vapor pressure, freezing point depression, melting-point elevation, and osmotic pressure. When a non-volatile (does not vaporize) solute mixes with the solvent, it lowers the vapor pressure of the solvent. This also raises the boiling point and lowers the freezing point.
To find the molar mass of the unknown substance, the colligative law has to be used. The law states that the freezing point and boiling point of a solution differ from those of the pure solvent by amounts that are directly proportional to the molar concentration of the solute.
Methods
To find the freezing point of cyclohexane we needed a test tube holder, 400 mL beaker, 600 mL beaker, large test tube, salt, water, ice, rubber stopper, stirrer, and thermometer. We took exactly 10 mL of cyclohexane using a buret and put it into the test tube. We then weighed out 50g of salt, mixed it in 400 mL of water, then added ice. Then the thermometer was inserted through the rubber stopper with the stirrer around the base of the thermometer to about halfway into the cyclohexane. The test tube is then placed in the test tube holder and the test tube containing the cyclohexane is placed into the ice bath solution. After the cyclohexane freezes to a solid,
Colligative Properties
Freezing-Point Depression and Molar Mass
By,
Andrew Klingsporn
Joby J.
Chem 212
Dr. Chandana Meegoda
2/11/2009
Purpose The purpose of this experiment is to determine the Molar Mass of an unknown substance using its freezing point depression.
Introduction
There are two types of mixtures; homogenous and heterogeneous. Homogenous mixtures have components that are uniformly mixed, while heterogeneous mixtures do not. A solution is a homogenous mixture that has two or more substances. A solution is mainly made of a solvent, while the solute is the smaller part of the solution.
A solution’s freezing point depression is a type of colligative property. There are four types of colligative properties: vapor pressure, freezing point depression, melting-point elevation, and osmotic pressure. When a non-volatile (does not vaporize) solute mixes with the solvent, it lowers the vapor pressure of the solvent. This also raises the boiling point and lowers the freezing point.
To find the molar mass of the unknown substance, the colligative law has to be used. The law states that the freezing point and boiling point of a solution differ from those of the pure solvent by amounts that are directly proportional to the molar concentration of the solute.
Methods
To find the freezing point of cyclohexane we needed a test tube holder, 400 mL beaker, 600 mL beaker, large test tube, salt, water, ice, rubber stopper, stirrer, and thermometer. We took exactly 10 mL of cyclohexane using a buret and put it into the test tube. We then weighed out 50g of salt, mixed it in 400 mL of water, then added ice. Then the thermometer was inserted through the rubber stopper with the stirrer around the base of the thermometer to about halfway into the cyclohexane. The test tube is then placed in the test tube holder and the test tube containing the cyclohexane is placed into the ice bath solution. After the cyclohexane freezes to a solid,