Tuesday, April 13, 2010

Bloggaday 58 – Calories, Labs, and Physics. Oh My!

Bloggaday 58 – Calories, Labs, and Physics. Oh My!
Well, I finally broke down and I’m posting a Physics lab report. Emoticon me is sad :-(. And apparently drooling a little bit. This particular lab tested the specific heat capacities of several types of metal

Lab Report 7
In this lab, I delved into calorimetry. Along with my four lab partners, I performed experiments to find out the specific heat capacity of a few different metals and an unspecified rock sample.
By performing these experiments, I will learn how to use several new instruments as well as how much heat different metals are able to absorb.
By transferring the heat of the metals into water, a substance we are very knowledgeable of, we can find the specific heat capacity of the various metals.
In question 1, I asked to consider a tub of ice water and a red-hot nail. First, I must describe the difference between heat, temperature, and internal energy. Heat is the transfer of kinetic energy. Temperature is the measurement of the kinetic energy of a substance. Internal energy is the sum of the kinetic and potential energy of the substance. Of the two substances, the nail is hotter. The tub has more internal energy though. The water would absorb all of the heat the nail lost. Some of that may then be lost to the air and tub itself.
For question 2, using too much water would skew the results. It takes a considerable amount of energy to heat water because of its high heat capacity. If there were an excess of water, much of the metal’s heating would be wasted heating water not needed to carry out the experiment. This would imply the rock had a lower specific heat capacity.
The answer to question 3 is rather simple. Measure the cup with out the water. Then, measure the cup and water together. Subtract the cup’s weight from the latter measurement, and you would be left with the weight of the water.
Upon comparing my results with the standard answers for question 4, I was somewhat torn. I got good results for aluminum and tin, with decent results for the large copper sample. There must have been substantial errors when it came with the smaller copper sample and the piece of zinc since both were over 50 percent different from the standard. Some errors likely included the metal sample not being in the boiling water long enough, the sensor either touching the metal in the water or a trapped area of heated water (for the tin and zinc since they actually had a higher specific heat than reported by the standard), or the amount of water in the cups (there was some debate as to the proportion of water to sample {more internal energy in a larger sample}). While not likely, our computer had problems, and there is a chance that maybe some of the equipment was also affected. Addressed in the handout, the equipment such as Styrofoam cups and other items are not perfect for this experiment.
When examining the difference between the specific heat capacity of metals and water for question 5, it becomes clear why there is a climate difference between deserts and land near the ocean. Water is able absorb a considerable amount of energy during the day without becoming extremely hot (while rock does). It also hangs on to that heat for a considerable amount of time (again, something rock doesn’t do). This is because of the difference in specific heat capacity.
Table I
Sample Ms (g) Mw (g) Th (C) Tc (C) Tw (C)
Aluminum (al) 30.6 89.5 98.9 22.1 27.2
Copper, Large (cu) 55.7 92.9 98.9 22.0 25.3
Copper, small (cu) 28.9 56.4 98.9 22.0 23.5
Tin (sn) 28.9 55.6 98.9 22.2 24.3
Zinc (zn) 29.1 53.5 98.9 22.2 28.0
Rock 7.8 50.4 98.9 22.7 25.3

Table II
Sample Cs (cal/g C) C*s (cal/g C) % error
Aluminum (al) .21 .215 2.3%
Copper, Large (cu) .074 .0919 19%
Copper, small (cu) .038 .0919 59%
Tin (sn) .054 .0509 -6.0%
Zinc (zn) .15 .0927 -62%
Rock .23 Unknown Unknown

After testing the various materials and doing the math, I got a broad range of answers. Aluminum was so close to the standard, that I find it hard to believe that there was no error. The in-lab conditions likely would have caused an error to decrease the specific heat capacity (exposure to air and less-than-perfect Styrofoam), yet I got basically the same answer. Something likely caused an error in the opposite direction. I feel the large copper sample was also within an acceptable range from the standard, the error more due to the conditions than conductor error. The small copper sample had a considerable error, but I don not know if the conditions were the sole cause. Other factors such as the sample not being in the hot water long enough could have caused the error. My sample of tin actually did better than the standard, which as discussed before, doesn’t seem likely. Some other error including instrument placement may have caused this. Zinc had the same problem, just on a much greater magnitude. The rock had the greatest specific heat capacity, but it was still less than a quarter of water’s capacity.
More than anything, this experiment demonstrated how much greater the specific heat capacity of water is compared to metals and rock. It also showed that different metals and materials have different specific heat capacities. I gained experience and knowledge about the experiment and instruments, but five people on one station is too much for extensive individual learning.

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