The purpose of this lab is to determine the molecular weight of a compound by measuring freeing point depression. When solutions are made, there is a process of breaking bonds and forming new bonds, which helps us understand the properties of the solution. To form bonds energy is required in the process of breaking down the bonds between ions and molecules in a solid phase. We know that both the standard freezing point phase transition and standard boiling point phase transition occur at atmospheric pressure. These temperature changes are referred to as the freezing point depression and the boiling point elevation. In the experiment we will, instead of heat, we will cool a liquid solvent and solution until it freezes and then we will be able to calculate the molecular weight of the solute.
In the experiment we will be using the data collection system, a hot plate, beaker, test tube, temperature sensor, Erlenmeyer flask, and a copper wire coil. We will begin the experiment by placing a 400mL beaker ¾ of the way full with water on top of a hot plate. We will then wrap the copper coil around the temperature sensor and place it inside a test tube. We will then use two clamps and a ring stand to hover inside the test tube and another to hold the test tube while it is submerged in the beaker. We will obtain 8g of lauric acid and transfer it into the test tube. A stirring bar is going to be placed inside the beaker and then we will turn on the hot plate and the stirring bar. After the crystals melt, we will transfer the crystals into a empty Erlenmeyer flask and begin to stir it to record our data. We will then repeat the process using an unknown sample.
I expect the my graphs will show and L-shaped curve starting at a high temperature then decreasing as time passes by and finally leveling out after a certain temperature. With the graph we will be able to determine the freezing point of the solvent and also the freezing point of the solution, from there we can calculate the freezing point depression. The curve on the graph is expected to look the opposite of the heating curve because the solution is being frozen. These results are important because they will follow the relationship of the heating curve except in reverse and create the opposite, a freezing curve. We will then be able to determine the molecular weight of an unknown substance by heating and cooling that substance and then determine its identity using the periodic table.