Specific Heat Lab
The purpose of this lab was to test and verify the specific heat of a metal. The students heated aluminum in order to understand and observe the specific heat equation in motion in a calorimeter. Using the calculations from the lab, the students were then able to calculate the actual specific heat obtained from the lab and compare it to the accepted value.
If the aluminum balls are heated in the test tube and poured into the water in the plastic foam cup, then the specific heat calculated from both trials will be precise because the accepted value for the specific heat of aluminum is independent from the mass of aluminum or water used.
Specific heat is the amount of energy required to raise the temperature of one gram of a substance by one kelvin The lab uses the specific equation in two separate ways: first to find the heat gained by water and then the specific heat of the aluminum. The first equation is: Heat gained by water=mass of water (g) X change in temperature DT (°C) X specific heat of water. The specific heat of water is 4.18 J/g* °C. DT represents the change between the initial temperature and the final temperature. Joule is the unit used to express energy and is equivalent to the amount of work done by a force of 1 Newton acting through a distance of 1 meter in the direction of the force. The second equation is:
Specific Heat of Aluminum = (Heat gained by water )/(Mass of metal (g)? ?T of metal (°C)).
The accepted value for the specific heat of aluminum is 0.90 J/g* °C. The lab also uses distilled water, which is water purified by a process of heating and cooling.
Independent Variable: Temperature of Aluminum Balls
Dependent Variable: Temperature of Water in Foam Cup
Controlled Variables: Pressure of water, air temperature, size of foam cup, type of foam, size of test tube, type of aluminum balls, size of beaker, type of thermometer,
- 2 Plastic Foam Cups
- 250 mL beaker
- Unspecific amount of tap water
- Unspecific amount of distilled water
- 2 18 X 150 mm Test Tubes
- Ring Stand
- Test Tube Clamp
- Hot plate
- Aluminum balls
- Filled 250 mL beaker half full with tap water
- Placed beaker on hot plate
- Measured mass of empty test tube
- Poured aluminum balls into empty test tube and measured new mass
- Attached test tube to ring clamp and attached ring clamp to ring stand
- Lowered test tube into 250 mL beaker and turned hot plate to 10, making sure not to touch the bottom of beaker
- Measured mass of plastic foam cup
- Filled plastic foam cup with distilled water at room temperature and recorded mass
- Measured and recorded temperature of distilled water
- Measured and recorded temperature of water in beaker when near boiling point
- Removed test tube containing metal from boiling water and poured metal into foam cup
- Stirred water in plastic cup slowly with thermometer and recorded highest temperature
- Carefully decanted water into sink and put aluminum on paper towel to dry
- Repeated steps 1-13 with second test tube and plastic cup
- Qualitative Observations:
- Excessive steam and bubbling from 250 mL beaker after reaching boiling point
- No water vapor observed on aluminum balls in test tube during boiling
- Difficult to stir aluminum balls within distilled water
Mass of aluminum = (Mass of test tube + aluminum) – (mass of test tube)
Aluminum: (76.75 grams) – (31.24 grams) = 45.51 grams of aluminum
Mass of water = (Mass of cup + water) – (mass of cup)
Water: (117.45 grams) – (2.13 grams) = 115.32 grams of water
DT of water in cup = (Temperature of water in cup with metal) – (temperature of water in cup)
DT of water: (27.5 °C) – (22.0 °C) = 5.5 °C
DT of aluminum = (Temperature of boiling water) – (temperature of water in cup with metal)
DT of aluminum: (99.6 °C) – (27.5 °C) = 72.1 °C
Heat gained by water = (Mass of water) X (DT of water) X (specific heat of water)
Heat gained by water: (115.32 grams) X (5.5 °C) X (4.184 J/(g*°C)) = 2653.74 Joules
Specific heat of aluminum = (Heat gained by water )/(Mass of metal (g)? ?T of metal (°C))
Specific heat of aluminum: (2653.74 J)/(45.51 grams X 72.1 °C) = 0.90 J/(g*°C)
Percent Error = (Experimental Value –Acccepted Value)/(Accepted Value) ? 100%
The values obtained in the lab were inconsistent with the accepted value of the specific heat of aluminum. Although trial 1 had a percent error of 9.8%, trial 2 had an even larger percent error range of 35.5%. This resulted in a 22.63% error for the average of the two trials. Both values had calculations below the accepted value, and the answers were neither accurate nor precise with the accepted value. In addition, trial 2 had less than half the joules of trial 1 although it contained a little more than half of the amount of aluminum of trial 1. Additionally, there was a bigger increase in temperature change of aluminum in trial 2 because there was a smaller increase in the temperature of water in trial 2. The objective of the lab was met since the heat gained by water was calculated and the specific heat of the aluminum was recorded. However, the hypothesis of the lab was not supported by the evidence because the specific heat values of the two trials were not precise. Although both calculations were independent from the mass of the aluminum recorded, trial 2 had a significantly lower specific heat than trial 1. The specific heat was lower than the accepted value for both trials because the DT of water and the DT of aluminum were not sufficient.
Evaluation of Procedure:
Although the procedure asked for a specific amount of water in the 250 mL beaker, it did not ask for a specific amount of aluminum balls in the test tube or distilled water in the foam cup. More importantly, the procedure did not request an amount of time for the aluminum in the boiling water. The temperature of the boiling water was recorded but the duration of the aluminum in the boiling water was not recorded in either trial. The lab asked for a foam cup as a calorimeter to reduce the loss of heat from the aluminum. The balance used only rounded to the hundredths place and the thermometer only rounded to the tenths place. In addition, the thermometer had an error of ± 0.1°C for each value recorded.
Improving the Investigation:
After step 10 in the procedure, another step could be added to increase the amount of time of the aluminum balls in the water to 5 minutes. This change would allow for more energy to transfer into the aluminum and create a bigger difference in the water in the foam cup before and after the aluminum is added. A balance to the thousandths place and a thermometer to the hundredths place would also give a more accurate answer. Instead of a foam cup, a reaction calorimeter could be used to measure the heat released and conserve energy more efficiently.