Calorimetry Chemistry Lab

Topics: Temperature, Heat, Thermodynamics Pages: 5 (971 words) Published: March 16, 2014
Determining the Specific Heat of an Unknown Metal

Objective:
To determine the specific heat of an unknown metal through the use of a calorimeter.

Background:
The specific heat of any substance represents the quantity of heat energy in joules required to heat one gram of the substances by one °C. The specific heat of a substance is dependent upon the temperature; this means that there is a temperature range for which the specific heat of a substance applies. For metals and metallic substances, this temperature range is usually large, but at lower temperatures. Their specific heats are very small because they only need a relatively small amount of energy to increase their temperature. On the other hand, insulating substances, such as the plastic foam in coffee cups, require a large amount of energy to increase their temperatures. Anyways, the equation used to figure out energy needed to increase temperature is:

Q (Heat Energy) = mass x Specific heat x Change in Temperature To determine the specific heat with the use of a calorimeter , the equation is :
QSubstance = -[ Qwater + QCalorimeter] which translates into (mcΔT)Substance = - [(mcΔT)Water + (CΔT)Calorimeter]

Materials:
Coffee-cup calorimeter
Water
Safety Goggles
Thermometer
Lab Apron
Ringstand
Tongs
Clamp
Graduated Cylinder
Test tube
Unknown Metal Sample
Hotplate
Triple Beam Balance (or other mass measuring equipment)

600 ml Beaker

Procedure:
1. Follow all safety guidelines prior to starting. Clear lab station. Gather all materials. 2. Set up the coffee-cup calorimeter as shown in the previous experiment in Figure 17-1. 3. Pour 75 ml, with a graduated cylinder, of cold water into the calorimeter and then cover the calorimeter. 4. Weigh out about 30 g of the unknown metal sample and record its identification number. 5. Pour 450 ml of water in a 600 ml beaker. Clamp the beaker onto a ringstand, place the hot plate underneath the beaker, and heat the water to boiling. 6. Transfer the metal sample to a clean, dry test tube and place it in the boiling water bath and let it stay there for 10 minutes to allow the metal to reach the temperature of the boiling water. 7. While the test tube is heating, record the temperature of the cold water in the calorimeter. 8. After the test tube is done heating, transfer the metal sample to the calorimeter and stir for about a minute. Record the highest temperature reached. 9. Repeat for trials 2 and 3. With this data, calculate the specific heat of the unknown sample. Data:

Trial 1
Trial 2
Metallic Substance used
Aluminum
Aluminum
Mass of substance taken, g
30.3
29.9
Mass of cold water, g
75
75
Temp of metal pellets (boiling water), °C
100
100
Initial temp of water, °C
22.3
23.1
Final temp of water, °C
28.7
29.1
Temperature change, ΔT
6.7
6.0
Specific heat of substance, J/g-°C
1.041
.950
Mean value of specific heat of substance, J/g-°C
.9955
Literature value, J/g-°C
.9
Percent error
10.61%

Calculations:

Error Analysis:

Discussion:
For this second part of the experiment, it initially was the same as the first part by recording the cold water temperature and ensuring that it maintained a steady temperature. Then we heated up a beaker with water to about 100 °C, and let the metal sample sit in there; thus, the rocks would have the same temperature as the water after being in the bath for 10 minutes. Then, after mixing the very hot rocks and the cold water in the calorimeter you would be able to manipulate the Q=mCΔT equation into giving you the specific heat of the metal, which in my case was calculated as .9955 Joules/ g-°C which is very close to Aluminum’s specific heat of .9 Joules/ g-°C.

Conclusion:
Our experimental results were extremely close with the actual specific heat of aluminum. However, there still could’ve been some errors in our experiment that altered the experimental data. For example, there might’ve been some residue...
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