Lab Report: Thermal Energy Transfer in Mixtures

Transcription

1 Lab Report: Thermal Energy Transfer in Mixtures Purpose: The purpose of this experiment is to discover how exactly the final temperature of a mixture, involving a substance and hot water, is affected and impacted by the type of substance used. This means that when hot water is mixed with another substance, it must be determined whether or not the temperature changes and why. The purpose is also to determine how and why the individual traits of each substance, such as the specific heat capacity, affect the final results. Hypothesis: It is believed that when a substance is mixed with hot water, the temperature of the mixture will vary due to the specific heat capacity of the substance. The lower the specific heat capacity, the greater the temperature variation. Therefore, the vegetable oil should be the substance which influences the final temperature of the mixture the most whereas the distilled water should influence it the least. Materials: Alcohol (at least 50g) Vegetable oil (at least 50g) Distilled water (at least 50g) Tap water (from the sink or a pitcher; at least 150ml) Scale (that can be zeroed) Electrical plug Calorimeter (with a cap that has one hole) Dropper Hot plate Large beaker Graduated cylinder (able to hold at least 50ml) Two thermometers with a stand Oven mitts Glass rod Paper towel Procedures: Thermal Energy Transfer Test 1. Make sure all materials are clean. 2. Connect the scale to the electrical plug. 3. Place the calorimeter (with no cap) on the scale and zero it. 4. Weigh 50g of alcohol. Note: If the amount of alcohol in the calorimeter exceeds 50g, use the dropper to obtain the exact amount. 5. Place the calorimeter containing the alcohol to the side. Ii is not required until later on in the experiment. 6. Pour a little more than 300ml of tap water into the large beaker.

2 7. Put the large beaker containing water on the hot plate. 8. Place one of the thermometers on the stand. 9. Put the thermometer connected to the stand into the water inside the beaker on the hot plate. Note: The thermometer should not touch the sides or base of the beaker; the stand should be beside the hot plate. 10. Connect the hot plate to the electrical plug. 11. Turn on the hot plate. Note: Make sure it s at its maximum temperature. 12. When the temperature of the water in the large beaker on the hot plate, recorded by the thermometer, is at approximately 90 C, using the oven mitts, pour 50ml of said water into the graduated cylinder. Note: Lower the temperature of the hot plate slightly or until it is at medium instead of maximum. 13. Put the large beaker containing water that was just used back on the hot plate. 14. Using the thermometer not used previously in the experiment, record the temperature of the water in the graduated cylinder. 15. Dry, using the paper towel, the thermometer just used, then record the temperature, using the same thermometer, of the 50g of alcohol in the calorimeter that was put aside earlier in the experiment. Note: When recording temperature, the thermometer should be in the substance for at least 30 seconds for the results to be accurate. 16. Clean and dry the thermometer quickly. 17. Gently pour the 50ml of water that is in the graduated cylinder into the 50g of alcohol in the calorimeter. 18. Quickly mix the new mixture using the glass rod. 19. Rapidly place the cap on the calorimeter and insert the now clean thermometer, which was previously used to calculate the temperature of the alcohol, into the hole in the cap. 20. Record the final temperature of the mixture. Note: Make sure the thermometer was submerged in the mixture for at least 30 seconds before the temperature is recorded. 21. Empty the contents of the calorimeter into the appropriate disposal bin. 22. Repeat steps 1-5 but using distilled water instead of alcohol. Since steps 6-11 heated enough water for all three of the experiments that need to be performed, simply check that the water in the large beaker on the hot plate is at the appropriate temperature (90 C). If it is not, then heat it once more. Repeat steps 12-20, but using distilled water instead of alcohol. Note: Every time the word alcohol is used, replace it with distilled water. 23. Repeat steps 1-5 but using vegetable oil instead of alcohol. Since steps 6-11 heated enough water for all three of the experiments that need to be performed, simply check that the water in the large beaker on the hot plate is at the appropriate temperature (90 C). If it is not, then heat it once more. Repeat steps 12-20, but using distilled water instead of alcohol. Note: Every time the word alcohol is used, replace it with vegetable oil. 24. Turn off the hot plate and unplug it. 25. Make sure all required temperatures were recorded through out the experiment. The independent variable is the initial temperature because it is what was manipulated through out the experiment. The dependent variable is the final temperature of the mixture. 2

3 Results: Results to the Experiments on the Thermal Energy Transfers in Mixtures Containing Water Substance Specific Heat Capacity (J/g C) Mass (g) Initial Temperature ( C) Final Temperature ( C) Alcohol Water Alcohol/ Water Mixture Xxxxxxxxxxxx xxxxxxxxxxxxx Xxxxxxxxxxxx xxxxxxxxxxxxx xxxxxxxxxxxxx Distilled Water Water Water/ Water Mixture Xxxxxxxxxxxx xxxxxxxxxxxxx Xxxxxxxxxxxx xxxxxxxxxxxxx xxxxxxxxxxxxx Vegetable oil Water Vegetable oil/ Water Mixture Analysis: 1. The substance which causes the greatest variation in temperature is the vegetable oil. 2. The substance which causes the smallest variation in temperature is the distilled water. 3

4 3. After performing this experiment, it has been determined that there is, in fact, a relationship between specific heat capacity and temperature variation. This has been discovered through the results obtained. The results suggest that the lower the specific heat capacity, the greater the temperature variation and vice versa. The reason for this is because of the fact that a lower specific heat capacity means that less energy is required to heat the substance, meaning that it is easier to heat. 4. It can be deduced that, through out the experiment, many thermal energy transfers occurred, many of these actually causing experimental errors. The thermal energy transfers included when the water was being heated on the hot plate and some of the energy was lost in the glass container, when the hot water was poured into the calorimeter containing another substance and the energy found in the hot water transferred to the other substance, when the calorimeter itself absorbed some of the heat and when some of the heat escaped the calorimeter before the cap could be put on. When one considers all of the previously mentioned examples of the energy transfers which took place, it can be deduced that they all have one thing in common; the energy was traveling from the hot environment to the cooler one. For example, the temperature of the other substances in which the hot water was mixed with were all pretty much at room temperature whereas the hot water was much higher, therefore, the thermal energy found in the hot water travelled to the room temperature substance; from hot to cold. 5. According to the law of conservation of energy, no energy is created only transferred or transformed. Therefore, the experiment had no choice but to be consistent with the law, even if the results themselves were not due to the occasional experimental errors, which include losing some of the thermal energy to the air and to the containers. Therefore, to test whether or not the results for each mixture are consistent with the law a 10% range (for the experimental errors) should be appropriate. Alcohol/ Water Mixture: Hot water Alcohol t = Ft - It Q = m x c x t Q = m x c x t HW t = 50 C - 68 C Q = 50g x 4.19J/g C x (-18 C) Q = 50.09g x 2.46J/g C x 28.5 C t = -18 C Q = -3771J Q = J A t = 50 C 21.5 C t = 28.5 C x = 10 x = = = Range: Since (the amount of heat absorbed by the alcohol) is in the in between and (the 10% range) then it can be said that this result was consistent with the law. Water/ Water Mixture: Hot water Distilled Water t = Ft - It Q = m x c x t Q = m x c x t HW t = 40 C - 66 C Q = 50g x 4.19J/g C x (-26 C) Q = 50g x 4.19J/g C x 18 C t = -26 C Q = -5447J Q = 3771J DW t = 40 C 22 C t = 18 C x = 10 x = = = Range:

5 Since 3771J (the amount of heat absorbed by the distilled water) is not in between and (the 10% range) than it can be said that this result was not consistent with the law. The reason for this is due to the possible sources of error in this experiment, such as the heat being absorbed by the glass and escaping before the cap could be put on the calorimeter. Vegetable oil/ Water Mixture: Hot water Vegetable oil t = Ft - It Q = m x c x t Q = m x c x t HW t = 59 C - 73 C Q = 50g x 4.19J/g C x (-14 C) Q = 50g x 2.0J/g C x 37 C t = -14 C Q = -2933J Q = 3700J VO t = 59 C 22 C t = 37 C x = 10 x = = =3330 Range: Since 2933J (the amount of heat released by the hot water) is not in between 3330 and 4070 (the 10% range) than it can be said that this result is not consistent with the law. The reason for this is due to the possible sources of error in this experiment, such as the heat being absorbed by the glass and escaping before the cap could be put on the calorimeter. 6. The ice will undergo the greater temperature change because of the fact that it has a lower specific heat capacity than water and, as was mentioned previously in this report, the lower the specific heat capacity, the greater the temperature change. When the ice is put in the water, due to the fact that the ice is cooler than the water it I being put it, the heat of the water is absorbed by the ice. Since the ice heats faster than the water due to its lower specific heat capacity, its temperature varies and increases much quicker than the water, thus explaining why ice will undergo the greater variation in temperature. Conclusion: After performing the experiments required in this lab, it can be concluded that the type of substance used in a mixture can influence the final temperature due to the specific heat capacity of the substance. The lower the specific heat capacity of the substance, the greater the temperature variation. This happens due to the fact a low specific heat capacity means that less energy is needed to raise its temperature, thus, in a mixture, the substance absorbing the water s heat will have a temperature that increases much quicker and thus creating a greater temperature variation. The results obtained following the experiment not only demonstrated this fact, but also supported the hypothesis given at the start of this report. The hypothesis stated that the lower the specific heat capacity, the greater the temperature variation and it mentioned that the vegetable oil would be have the greatest temperature variation, the distilled water the smallest temperature variation and the alcohol would be in between these two variations. The results proved the hypothesis correct because of the initial temperature and final temperature recorded for each substance. If these temperatures were to be subtracted, then it would demonstrate that vegetable oil had, in fact, the largest variation while distilled water had the lowest. Some of the possible sources of error in this lab are those mainly involving heat losses. When the hot water was poured into each calorimeter, a large amount of heat not only escaped before the cap could be put on the calorimeter, but some of the thermal energy also remained in the glass of the graduated cylinder in which the hot water was originally in while the other 5

6 lost thermal energy might have been absorbed by the air and the Styrofoam walls of the calorimeter. Another possible source of error was during the measuring the final temperature of the alcohol/ water mixture. For some still unknown reason, the alcohol/ water mixture exploded from the calorimeter in which it was held, thus causing the experimenters to be covered in the mixture and the calorimeter to become deformed. This might have caused the temperature to be considered wrong since a great amount of the mixture was no longer in the calorimeter. If the experiment was to be performed again, some parts of the experiment would be done differently. For one, the hot water used for the experiments would have been hotter, since the high sixty and low seventy degrees were not very reliable numbers to use. Having arranged so that the water boiled on the hot plate and then having poured it in the graduated cylinder would have ensured the experiment to have temperatures that were higher and that thus demonstrated the temperature variations more clearly. Another action that would improve the protocol of the lab would be by using a better calorimeter who s cap was tighter and less breakable. 6