Sodium Chloride Lab Report

1. Sodium Chloride has a higher boiling point than water, so when salt is added to water, the solution has a higher boiling point than pure water. The sodium ions and chloride ions present in sodium chloride disassociate and dissolve in water. These ions interfere with the dipole interactions that occur between molecules of water. The dissolved sodium ions and chloride ions require more energy to separate from the water molecules in the solution than the water molecules from themselves, so the boiling point of the solution is elevated as a result.2

2. The compounds and solvents used have fairly low melting points, so the use of a Bunsen burner would likely result in irreversible changes (ex: combustion) to the some of the compounds/solvents.

3. Benzoic Acid is the additive listed that would have the greatest impact on the phase change of the solution. Benzoic Acid is a caustic substance, and as a result would have the greatest likelihood of altering the solution. Furthermore, Benzoic Acid has two NFPA 704 warnings listed, and the other additives have none.3

Freezing Point Depression of Water

Introduction
The freezing point of a volatile solution can be elevated or depressed by adding solvents to the solution. The interactions between the molecules of the solvent and the solute cause the depression of the freezing point of the solution. This occurs because the solvent particles prevent the solution from freezing as readily.1 The use of road salt is an example of this process in everyday life. In this experiment, the effects Benzoic Acid and Camphor have on the freezing point of tert-butanol is measured. Vapor Pressure is the measurement of the pressure exerted by a liquid or gas while in a state of thermal equilibrium. Benzoic Acid and Camphor both have higher vapor pressures than tert-butanol, and as a result the vapor pressure of the tert-butanol solution should increase when either is added. As a result of their lower vapor pressures, Benzoic Acid and Camphor both have a lower freezing point than tert-butanol. When Benzoic Acid and Camphor are added to tert-butanol, the solution will have a lower freezing point than pure tert-butanol.2 This hypothesis was tested by mixing tert-butanol with Benzoic Acid and Camphor in separate trials, then heating and cooling the solution. The difference in temperature of the solution recorded displays the effect the additive substances had on the freezing point of tert-butanol.
Methods
The first trial was the control group of the experiment, it consisted of only tert-butanol.

The three remaining trials were the experimental groups containing Benzoic Acid and Camphor separately with tert-butanol. 6.305 of tert-butanol was placed in a large test tube, the same amount was used for each trial. The solution was then brought to 50 C using a hot-plate. The temperature was monitored and recorded by a Lab Quest 2 Connected Sciences System. The test tube was held in place using test-tube tongs, and the thermometer was suspended in the solution to ensure accurate measurement. The solution was brought to 50 C, and then the temperature was then recorded at 10 readings per second. After several readings were recorded, the test tube with the solution in it was placed in an ice water bath. The temperature of the solution was monitored for several minutes at 10 readings per second in the ice water

bath.
Results
Figure 1.
Trial Additive Mass (g) Mols of Substance Molarity Molality
1 5.00 0.067 1 N/A
2 Benzoic Acid 0.29 0.004 0.634 0.8
3 Benzoic Acid 0.61 0.005 0.793 1.0
4 Camphor 0.38 0.002 0.317 0.4

Figure 2.

Trial Additive Maximum Temp. C Minimum Temp. C
1 None 50.4 13.0
2 Benzoic Acid 54.6 16.4
3 Benzoic Acid 67.8 14.2
4 Camphor 66.4 12.6

Figure 3.

Figure 4.

When Benzoic Acid and Camphor were added to tert-butanol the peak temperature of the solution was greater than the pure tert-butanol solution. The experimental groups reached greater temperatures than the control group when heated. The experimental groups heated faster than the control groups. Tert-butanol in trial 1 froze at a higher temperature than the trials than included additives in the form of solvent.
Analysis
There was a significantly greater amount of tert-butanol present than the additives in each trial, yet the small amounts of solvent added had a significant effect on the temperature of the solution (Figure 4).

This implies that the vapor pressure of both benzoic acid and camphor are significantly greater than the vapor pressure of tert-butanol. In trial 4 there were less moles of camphor present than in either trial of benzoic acid, yet it had a similar effect on the freezing point of tert-butanol (Figure 3). This supports that camphor has a much higher vapor pressure than both tert-butanol and Benzoic acid. When benzoic acid was added to the solution in trial 3 in greater amount than trial 2, the temperature change was greater, further supporting that benzoic acid has a higher vapor pressure than tert-butanol. This is supported by the data, the experimental groups all reached greater temperatures, and remained liquids at lower temperatures (Figure 3). The accuracy of that recorded data may have been impacted by human error. The actual freezing points of the solutions were difficult to determine accurately due to the equipment used, although the trends overall trends of the experiment were still visible. The method of temperature measurement may have affected the outcome of the experiment. The temperature attachment for the Lab Quest 2 system was held in the test tube by hand, and likely came into contact with the test tube the solution was in. The test tube likely

experienced more rapid temperature fluctuation due to being in direct contact with the hot plate or ice water bath. This would have exaggerated the temperature change of the solution when the device came into contact with the test tube.

Conclusion
The hypothesis was supported by the results of the experiment. The experimental groups containing benzoic acid and camphor reached greater temperatures when heated, and froze at lower temperatures than tert-butanol. This supports that benzoic acid and camphor have higher vapor pressure’s than tert-butanol, and have lower freezing points as a result.

Data Analysis
1. The freezing point of tert-butanol is 74.12 F
2. The temperature changes in the experiment were gradual. The method of heating, and then transferring the solution to the water bath may negatively impacted the accuracy of the results.
3. According to that data, Camphor and Benzoic Acid had similar effects on the freezing point of Tert-butanol. Both additives decrease the freezing point of water, because the more energy is required to separate them from water molecules in the solution.