Lab Report 3 - Specific Heat of a Metal PDF

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Specific Heat of a Metal Brayden Hill, Hannah Hodges, and Stephen Mosley CHEM 1211K M-F 8-11:50 Dr. Peter Rosado Flores

Abstract The purpose of this lab was to use calorimetry to determine the specific heat of a metal. If the specific heat of an unknown metal is calculated, the identity of the unknown metal can be revealed. The revealing of the unknown metal allows the metal to be used in compounds without fear of danger. This identity of the metal is very important to the well being of the chemist using it as well as the safety of the public. At first observation, the metal being tested had a low density. It appeared to have a grey color, and it was shiny. After the metal was tested in the calorimeter, it can be stated that the unknown metal was aluminum. Although the experiment yielded a relatively high percent error, the density given in the table and the density calculated in the lab were close enough to confirm that the metal being tested was aluminum.

Introduction Since the dawn of chemistry, the classification of the elements has evolved many times as they discovered more about how the world on the atomic level worked. Now, understanding the structure of the atom, the names of subatomic particles, and the names of elements are practically common knowledge in the western world. However, just inventing and knowing where the lines are drawn delineating the types and names of the elements is not enough to practice chemistry; chemists also have had to come up with methods of figuring out how to classify a given substance not previously known about. One of these, among the most simple and hands on methods of classifying elements, is calorimetry. Calorimetry is “a set of techniques employed to measure enthalpy changes in chemical processes,” where enthalpy refers to the amount of heat in the system.¹ Studying the heat contained in a system and how much of it is released of absorbed allows experimenters to study chemical reactions to decide if they’re endothermic or exothermic, and more relevantly, classify substances. To do this, a device called a calorimeter is used. A calorimeter is a device used to measure the amount of heat involved in a chemical or physical process.”² In this experiment, a styrofoam cut was used to insulate the heat in a volume of water, and the substance was placed in a glass beaker to allow the transfer of heat to and from the metal and water. By heating up a given substance to a known temperature, placing it in the volume of water of a known temperature and seeing how much heat energy is transferred between the two substances, the heat capacity of the substance can be found which can be used to classify the element. The heat capacity is “amount of heat required to raise the temperature of an object by 1 [degree] Celsius.”³ This value is unique to the specific substance being studied whether it be an individual element or a molecule. Since the heat capacity of water is already known, we can equate the change in energy of the water with that of the substance, compare that with its temperature change, and discover its heat capacity. ⁴In this experiment, there were many sources of error hindering the ability to rely on the heat capacity found alone, so we also found the given object’s density to classify it.

Procedures 1) The logger pro system was set up with two temperature probes running simultaneously. 2) Qualitative observations were recorded for the unknown metal. 3) The mass of the unknown metal was weighed and recorded. 4) The unknown metal was carefully slid into the glass test tube. 5) A hot water bath was set up in a 250 mL beaker. Clamps were used to lower the test tube into the water bath without it touching the glass beaker. a) Made sure the water level remained higher than the metal piece in the test tube. 6) One temperature probe was placed in the hot water bath not the test tube. The collection began and the initial temperature was recorded. a) The probe did not touch the glass. b) The hot plate was turned on. 7) The water was heated until boiling, and then continued heating for 10-20 minutes. 8) The temperature of the boiling water was recorded like that of the metal piece. 9) The water in the beaker was replenished to make sure the water level in the beaker remained higher than the metal piece in the test tube. 10)A calorimeter with a temperature probe and clamp was set up and its mass was recorded. 11) The calorimeter was filled with 130 mL of room temperature distilled water, and the mass of the water was recorded. 12)The initial temperature of the water in the calorimeter was recorded by monitoring the temperature of the calorimeter with the second temperature probe. 13)The test tube clamp was used to quickly remove the test tube from the hot water bath. 14)The metal piece was carefully transferred into the calorimeter by sliding it out. a) No water was allowed to spatter out. 15)The lid was quickly put on the calorimeter with the temperature probe without touching anything.

16)The temperature was monitored until it reached its maximum point. The system was allowed to level out before stopping collection. 17)The final temperature of the metal and the water was recorded.

Data and Calculations Table 1- Specific Heat Lab Data Variable

Results

Qualitative Observations of the unknown metal

Cylinder shaped, super light compared to the over unknown metal, silverish color

Mass of Unknown Metal

17.762 g

Initial Temp of the Hot Water Bath

18.3 C

Temp of Boiling Water

100.1 C

Mass of Calorimeter

120.332 g

Mass of Water in the Calorimeter

130.0 g

Initial Temp of Water in Calorimeter

19.3 C

Final Temp of Metal

22.4 C

Final Temp of Water

22.4 C

Table 2 - Physical Properties of Potential Unknown Metals Metal

Specific Heat Capacity

Density

Aluminum

0.900 J/g C

2.70 g/cm

Cadmium

0.232 J/g C

8.65 g/cm

Cobalt

0.421 J/g C

8.86 g/cm

Copper

0.387 J/g C

8.96 g/cm

Lead

0.128 J/g C

11.36 g/cm

Tin

0.210 J/g C

7.28 g/cm

Zinc

0.390 J/g C

7.13 g/cm

Calculations 1) Density of Unknown Metal = Mass of Unknown Metal ÷ Volume of Displaced Water a) Density of Unknown Metal: 2.73 g/cm³ = 17.762 ÷ 6.50 2) M metal x C metal x ΔT metal = -M water x C water x ΔT water a) M = Mass (g) b) C = Specific Heat (J/g C) c) ΔT = Temperature Change i)

Specific Heat of Unknown Metal: (17.762)(C metal)(100.1 - 22.4) = -(130)(4.179)(22.4 - 19.3)

ii)

1380.107 C = 1684.137

iii)

1.22 J/g C = 1684.137 ÷ 1380.107

3) Percent Error = [(Experimental Specific Heat - Actual Specific Heat) ÷ Actual Specific Heat ] x 100% a) Percent Error for Aluminum: 35.56% = [(1.22 - 0.900) ÷ 0.900] x 100%

Results and Discussion On first inspection, the substance given was a two to three inch cylinder with a half inch diameter, gray, hard, metallic, and matte. The mass of it was recorded as 17.762 grams, so the metal was not too dense. The density was found to be 2.73 grams per milliliter, only .03 g/mL off from the accepted density of aluminum. Aluminum’s physical appearance also went along with that of the substance, so going forward with the experiment, this made sense. However, when the experiment was completed, the

heat capacity was found to be .32J/g*degrees C higher of the accepted heat capacity of aluminum with a percent error found to be 35.6 percent. This is strange seeing as the density found only made sense with aluminum. It seems the right care was not given to the procedure to make sure heat wasn’t lost to the surroundings. By thought, it can be seen that if the metal were cooled by the air before being put in the water to transfer heat, it would seem as if the water cooled it down even more than it actually did, and the metal would have leveled out with the water at a lower temperature. The energy exchange would have seemed lower, and so the specific heat should have been lower than expected. Some sources of error could have been energy loss to the surroundings in the transferring over of the metal to the water; inaccuracy of the initial temperature of the metal (was not actually taken, but was speculated to be the temperature of the boiling water it was in for a period of time); inaccuracy of the amount of water that actually used for energy transferred (was taken to be 130g=130mL but was not actually measured because the scale wasn’t working); and the fact that some water spilled on the table during transfer. From all this, it makes more sense that the measured specific heat would be off from the accepted value, although it still is strange that it is higher than the accepted rather than lower. Still, the value of this experiment still came through from its completion. Calorimetry is an integral category of methods to the field of chemistry as it pertains to the specific study of one of the most fundamental elements of chemical reactions and the atomic world, heat and energy. Not only can it be studied to see how energy moves from particle to particle, but to study specific particles and classify them too.

References 1) Calorimetry, 16 June 2019. LibreTexts Library. https://chem.libretexts.org/Bookshelves/General_Chemistry/Map %3A_Chemistry__The_Central_Science_(Brown_et_al.)/05._Thermochemistry/5.5%3A_Calo rimetry (accessed 2 July 2019). 2) Calorimetry. BCCampus Open Textbooks. https://opentextbc.ca/chemistry/chapter/5-2-calorimetry/ (accessed 2 July 2019). 3) Heat Capacity and Specific Heat, 5 June 2019. LibreTexts Library. https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Book %3A_Introductory_Chemistry_(CK12)/17%3A_Thermochemistry/17.04%3A_Heat_Capacity_and_Specific_Hea t (accessed 2 July 2019). 4) Keen-Rocha, L. Principles of Chemistry I, Hayden-McNeil, LLC: Plymouth, MI, 2018. 5) Zumdahl, S. S.; Zumdahl, S. A.; DeCoste, D. J.; Adams, G. M. Chemistry. 10th ed.; Cengage Learning: Boston, MA, 2018....