By the end of this lab your students should have practical experience observing changes of state freezingwhich occur with variations in temperature and can be predicted by knowing the properties of the material DCI - PS1. Calculate the mass of unknown sample transferred to the test tube by difference.
The solvent that will be used in this experiment is para-dichlorobenzene, shown in Figure 2 below. The second line connects points where solid and liquid coexist.
After transferring some of the unknown, reweigh the remaining unknown sample and its container. The amount you added should be between 1 and 3 grams. Add this mass to the mass of unknown transferred in Step 8 to obtain the total mass of unknown added to the large test tube.
If you do spill some you will need to start this step over with a fresh sample of weighed PDB. If you transferred less than 1 gram of unknown, you will need to add more unknown to the large test tube and reweigh before proceeding.
Reweigh and record the mass of the test tube and the PDB. Cause and Effect - Cause and effect relationships may be used to predict phenomena in natural or designed systems.
Continue for at least 4 minutes after the first solid starts to appear, or until the mixture has solidified to a point that you are no longer able to stir it. Do not allow any of the acetone or PDB-unknown mixture or rinse to go down the sink.
Near the melting point you will observe crystals of PDB in the liquid, and these will increase in amount as the cooling proceeds. Monitor the temperature of the PDB-unknown mixture as before.
Record the temperature every minute and note the physical state of the wax. There may be some supercooling, as evidenced by a rise in temperature shortly after the first appearance of crystals. This behavior is shown in Figure 3 below. Para-dichlorobenzene is used in mothballs and urinal cakes, and so it may have a familiar smell, however direct inhalation of its vapors may be harmful or even toxic.
Note the temperature at which any solid first appears.
This effect is called supercooling, and is a phenomenon that may occur with both the pure liquid and the solution see Figure 3. Therefore, the temperature at which the equilibrium vapor pressure reaches atmospheric pressure is higher for the solution than for the pure solvent.
The innocent kids get the message and self-police their group. Weigh a clean dry large test tube using an electronic balance, and record its mass. Carefully transfer about 2 grams of the unknown solid into the large test tube, taking great care that none of the unknown sample is spilled during this process.
Remove the hot water bath as before, and dry off the outside of the test tube with a paper towel. I buy cheap non scented candles and use a sharp knife to cut in into pieces that will fit into a test tube. I stess that the wax is hot and they will feel it if any lands on their skin.
Safety The PPE for this lab includes safety goggles, lab coat and nitrile gloves. Once again, some supercooling might occur.Molecular Mass by Freezing Point Depression Prelab Purpose Graphs Conclusion 1.
To determine the molecular mass of an unknown substance by finding the freezing point of two solutions (BHT and para-dichlorobenzene, and BHT and the unknown. Purpose: The purpose of this lab was to determine the freezing point of pure water, the experimental van’t Hoff factor for a substance and the molar mass of an unknown solution.
Part 1: Determining the Freezing Point of Pure PDB. Assemble a stand with ring clamp and a wire gauze inside one of the fume ultimedescente.com a Bunsen burner below the wire gauze adjusting the height so that the flame will be.
Lab 3 - Freezing Point Depression; Lab 3 - Freezing Point Depression In Part A of this experiment, you will determine the freezing point of pure stearic acid. In Part B, you will measure the freezing point depression caused by adding varying amounts of lauric acid to stearic acid and compare these measured values to your calculated values.
Determining Freezing Points Lab. Determine Freezing Points Lab - Graph. NOTE: Leave the thermometer in the test-tube for the entire experiment. 4) Wait until the liquid in the thermometer has stopped rising. Record this temperature. Indicate at what point the liquid became a solid.
Experiment 5 Freezing Point Depression OUTCOMES After completing this experiment, the student should be able to: After determining the freezing point and actual values from your lab section and calculate the average value of K f for t-butyl alcohol. 6. How constant was the K f.Download