Lab 2B: Heating and Cooling Curves of a Pure Substance

Lab 2B was was done in class on October the 4th. It involved the measuring of the freezing and melting points of Dodecanoic cid. It was interesting to see how quickly change of state occurred during the experiment.

Equipment:

Ring stand
Buret clamp
Hot plate
beaker with water (hot and cold)
2 Thermometers
Safety goggles
1 Test Tube
Dodecanoic Acid
Paper to record observations

Procedure:

(Part 2 was done first)

Part 2:
We started off by putting on saftey goggles. Followed by gathering materials needed to conduct the experiment. Students in groups of 2, were given liquid Dodecanoic acid in a test tube. A thermometer was placed in both the acid and the water beaker. The test tube was then suspended inside a beaker filled with cold water by a buret clamp attached to the ring stand. Students then observed the acid as it slowly reached its freezing point. Temperature change was recorded in 30 second intervals, along with observations. Once the acid reached 25 Degrees Celsius, observations and recordings of time intervals were stopped, and students moved on to part 1.

Part 1:
Once the acid had reached 25 Degrees Celsius, students turned on there hot plates. The hot plate's temperature was turned to 2. The cold water from the beaker was replaced by hot water, and placed on the hot plate. The acid was once again suspended inside the beaker of water. Time intervals of 30 seconds were recorded along with observations while the acid reached its melting point. Once the acid had reached 50 Degrees Celsius, observations were stopped and the experiment was complete.

Result:

After preforming the experiment, the melting and freezing points were recorded. The melting point was recorded at 40 - 45 Degrees Celsius, and the Freezing point at 30 - 35 Degrees Celsius. The recording of the temperatures came out very unexpectedly. There were some time intervals where there was no change in temperature, this is because all the energy being transferred from the water to the acid was changed into kinetic energy and used to help break the attractions between the molecules in the acid instead of raising the temperature. Thus creating plateaus in the temperature change graphs made. It was interesting to do this experiment. What made it interesting was knowing that the temperature in which Dodecanoic acid melts and freezes is so close together, and can be changed very quickly.