Freezing Point Lab

After each of the solids were completely dry, each was placed into a MelTemp device. The temperature at which each solid began to melt and completed melting was recorded.

The melting point of the final product, diphenylacetylene, was found to be 65-68 degrees Celsius which is right around the ideal 61 degrees Celsius melting point; this shows that purification during the lab worked and that the sample was almost 100% pure. Since only 0.01g of diphenylacetylene was collected and the theoretical yield was calculated to be 0.049g, this experiment had a 20.41% yield. A few sources of error that explain the low percentage could be the loss of crystals when transferred from the test tube to the suction apparatus or when they were transferred from the suction apparatus to the filter paper to be dried and then weighed. Crystals could have also been lost if more than 5 drops of methanol was added because excess methanol would dissolve the crystals. The experiment was successful when looking at the crystals collected from the addition step and the elimination step; however, to improve the percent yield and collected product the the test tubes could have been allowed to cool down in the ice bath past the 5 minutes to ensure all the crystals formed

Testable Question: Does the type of material placed on ice affect the rate in which the ice melts? Purpose: When it snows in the winter time or rains and freezes, what can we use to melt away the ice, snow, and sleet faster than salt, if there is anything that melts ice faster than salt. If there is something that can melt the frozen precipitations quickly, it will benefit us. Also, melting the ice at a faster rate will lower the rate of slips and falls even faster.

The vial was removed from the heat and cooled to room temperature. The spin vane was rinsed with 2-3 drops of warm water over the conical vial. The vial was cooled to room temperature then placed in an ice bath for 15 minutes. The liquid was decanted from the mixture and the resulting crystals were dried on filter paper. The crystals were then placed on a watch glass for further drying. The crystals were weighed and a small sample was placed into a capillary tube for melting point determination.

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.

To start this laboratory, it must first label two transformation tubes of different color; one with – DNA and the other with + DNA. Then, using a P-1000 micropipette adds 250 ul of the ice cold transformation solution (CaCl2) into each tube and places both tubes on ice. Using a disposable sterile inoculating loop to transfer colonies of E. coli bacteria from the starter plate to the +DNA tube. Immerse the loop in the CaCl2 solution in the transformation tube and spin the loop until all bacteria is incorporated into the transformation solution. Repeat this step with the – DNA tube. Using a P-10 pipette, transfer 10 ul of pGLO directly into the + DNA tube. Tap the tube lightly with a finger to mix. Place both tubes onto ice, and incubate for 10 minutes.

Introduction The purpose of this lab was to explore the colligative properties, in this case freezing point and freezing point depression, of the solvent p-xylene. The freezing point of p-xylene was obtained using the MicroLab program and a thermistor temperature sensor. From this data, the freezing point depression constant, kf, could be found, as well as identifying three unknown solutes by calculating their molar masses.

The purpose of this experiment was to determine which temperature (hot, cold or room temperature) affects the growth of crystals the most.

After experiment A was completed it was exceptionally clear that there was an obvious difference between the melting points of all mixtures, yet Mixture 1 and 2’s melting point ranges are much narrower than that of Mixture 3’s, as seen on Table 1.A. The results from this experiment help to clearly identify the three unknown mixtures by comparing them to the established melting points of naphthalene and benzoic acid. Mixture 1’s melting point range of 123-125.5 degrees Celsius is in the vicinity of benzoic acid’s melting point of 122 degrees Celsius1; a reason for the discrepancy may be the Mel-Temp was set to rise in temperature too quickly. Mixture 2’s melting point range of 82.3-84.2 degrees Celsius matches closely to naphthalene’s melting point of about 80 degrees Celsius1; similarly this process would have been more accurate had the Mel-Temp been programmed to rise in temperature at a slower rate. And finally the composition of Mixture 3 is most likely a combination of the two, due to the low as well as very wide melting point range, both characteristics of a combination of different compounds2.

A plastic transfer pipette was used to put approximately 2 mL of p-xylene, obtained from the fume hood, into a clean, dry polypropylene test tube. The calibrated temperature probe was dried carefully with a paper towel, and then was put in the test tube. The measurement program was started and the test tube was lowered into an ice water bath, with the p-xylene in the test tube being below the surface level of the ice water. The p-xylene was stirred continuously with the temperature probe until the temperature graph leveled off. The program was stopped and the data was taken for 10 or 15 seconds after the graph leveled off. The p-xylene test tube was put in a beaker until the p-xylene thawed, and then was poured into the waste jar. The test was put in the box provided for used test tubes in the fume hood. To determine the freezing point of p-xylene, the range of data where the temperature had leveled off was used to obtain the average by clicking on Column

The literature value for the enthalpy change of the last reaction which was provided by our teacher is -97 kJ mol-1. Agreeing this value, our result can be considered accurate.

The control experiment for this investigation will be the experimental setup of 5 trials using 5oC as the temperature. All the steps in the method will be followed.

It is suspected that the freezing point is 64.1oC. Due to the short temperature plateau, It is difficult to determine if the freezing point occurs at during the interval (6:00-6:10). However, it appears to be have been the most reasonable determination for freezing point in comparison to the rest of the plot.

As stated, our solvent in this lab will be tert-butanol. We start by recording the freezing point of this substance without anything added. Then, we add various

Considering the results, one could conclude that freezing has an affect on the toughness properties of the samples. Although, the quantitative mechanical properties changes by freezing the samples, the qualitative behavior of the samples does not show any obvious changes in the toughness properties, which is a macro-mechanical property.\\