Hot Water Lab September 4, 2003

Transcription

1 Lab Partners: Johnny Smith Janie B. Good Susie S. Marte Hot Water Lab September 4, 2003 Period 2 September 10, 2003 Introduction: The purpose of the hot water lab is to determine the of the water with a thermometer that only has s up to 40 o C. This lab will also demonstrate the usage of the specific heat equation. In order to accomplish this a calorimeter will be used to avoid any heat loss during the experiment. There will be two cups of water used, one with the hot water and one with cold water. When the two amounts of water are added together the change in and the specific heat of water will be used to determine the original of the hot water. The possible outcome is that the of the water will accurately be determined. Materials & Methods: Materials: Thermometer Chemicals: H 2 O - dihydrogen monoxide (water) Calorimeter ice water, H 2 O Lid for calorimeter hot water, H 2 O Stirring rod Source for hot water Triple-beam balance Non-Standard Apparatus:

2 The above image is of various calorimeters. A calorimeter is used to insulate an experiment to avoid any heat loss so more accurate results could be obtained. The calorimeter on the right shows a Styrofoam cup with a lid. This is similar to the one used in this experiment. Procedures: Obtain all the equipment, the cool water, and ice. Wait to obtain the hot water until it is needed to avoid any additional heat loss. Take the Styrofoam cup and find the mass of the empty Styrofoam cup using a triple beam balance. Make sure the balance is on zero before placing the cup on the tray. Place the empty cup on the tray and move the weights to re-zero the balance. Carefully read the scale starting with the hundreds, then the tens, and finally the ones. Remember to estimate the decimal place correctly for a more accurate reading. Once the mass is obtained, place some cool water in the cup; add some ice to the cup of water. Allow the ice to melt completely before continuing. This was done to cool the water to a very low (as close to zero as possible). Remove any remaining ice chips to ensure good measurements. Find the mass of the cold water by placing the full of cup of cold water on the tray of the balance and following the same mass procedures as above. The mass of the cold water is determined by taking the difference between the mass of the empty cup and the mass of the cup plus the cold water. Record all mass measurements in a data table. The of the cold water was determined by using a thermometer. Place the thermometer into the cup of cold water being careful not to touch the sides or bottom of the cup. Allow a few minutes for the to stop moving. Carefully read the height of the red line and record this value in a data table. Determine the mass of the calorimeter used by following the same mass measurement procedures listed above. Now, obtain a sample of the hot water and place it in the calorimeter to avoid any heat loss. Move quickly to avoid any additional heat loss and determine the mass of the calorimeter and the hot water using the mass

3 procedures above. The mass of the hot water is determined by taking the difference between the mass of the calorimeter and the mass of the calorimeter plus the hot water. Be sure to record all mass measurements in a data table. Add the cold water to the hot water that is inside the calorimeter. Place the thermometer into the top of the calorimeter and follow the procedures above to determine the final of the combined cold water plus hot water. Record the in a data table. Repeat these procedures three times to average out additional error. Use the equations below to calculate the beginning of the hot water. q rxn = - q sur q = heat measurements made in the calorimeter or q hot = - q cold q sur = m x C x (T f - T i ) m = mass of the water, C = specific heat, T = Therefore; m x C x (T f - T i ) = -( m x C x (T f - T i ) ) where the hot water portion is on the left side of the equation and the cold water portion is on the right side of the equation. The specific heat of water (C) is J/g o C. Results: Data: Temperature and Mass of Cold and Hot Water Trials Initial cold Final cold Initial hot Final hot Mass of cold water (g) 1 2 Place all your data in the data table. 3 Avg Mass of hot water (g)

4 Calculations: Be sure to include any and all calculations no matter how elementary they may seem. Also, include the equations again to be sure the calculations make sense to the reader. For this lab, include mass by difference calculations, the specific heat calculations, and the average calculation. Obtain the actual value of the hot water from your instructor. Then, complete the percent error calculation as well (see below). The actual value of the hot water was 84.3 o C and the average of the hot water from this investigation was determined to be 78.9 o C. Percent error = actual value - lab value x 100 = x 100 = 6.41% actual value 84.3 Graphs: For this lab there were not graphs to present data. Discussion: The main reason for the discussion section is to summarize your data. To assist you in this you mat start with the questions asked during the lab or on the lab handout. Be sure to answer any and all questions as detailed as possible. DO NOT write them as question answer question answer - etc. Answer each question as completely as possible in paragraph format. Be sure to be as specific and detailed as possible. Use the procedures, results, data, and calculations as support for each statement made. Remember, unsupported answers do not carry any weight! I do not give any examples here, just be sure to follow the 6-trait grading rubric and you will do fine. After all questions are answered, go back and make sure your data is sufficiently summarized.

5 Conclusions: Using a calorimeter, a thermometer that only goes to 40.0 o C, and water, the of hot water was determined. Obtain a sample of cool water and lower the even further using ice chips. Get the of the cold water as close to zero as possible. For this investigation the of the cold water was reduced to 2.1 o C. Using a triple-beam balance, the mass of the cold water was determine to be 56.2 g and the mass of the hot water was determine to be 53.4 g. The two samples of water were added together inside a calorimeter and the was allowed to stabilize. The final was obtained using the thermometer that only went to 40.0 o C. The final for this investigation was 22.1 o C. Using this data and the specific heat of water (which is J/g o C) the average of the hot water was determine to be 78.9 o C. The results showed a few pieces of data that did not seem to relate to others. In one trial, the final was actually lower than the of the cold water alone. In another trial, heat loss occurred when the hot water was obtained too quickly and the procedures did not call for it yet. These results were not used to determine the average but were included in the data table. Additional trials were run to still obtain more accurate results. The data showed trends that the quicker and more effectively the procedures were completed, the less heat was lost from the hot water. Thus, more accurate readings were obtained. Due to this several additional trials were completed to correct and human error in the procedures. The errors that were introduced in this investigation were the heat loss, not allowing the ice to melt completely into the cold water, and waiting too long to take the final. There was also a human error in that the calorimeter lid was left off in trial 6. The heat loss was due to human error

6 and the quality of the calorimeter used. To avoid as much heat loss as possible the calorimeter design was improve upon. A double Styrofoam cup was used as the base and a lid was constructed from a piece of Styrofoam. After realizing the ice had to melt completely, the wait time was increased to allow the ice to melt. In later trials, any additional ice that remained was removed prior to continuing. It was difficult to determine the final and a few trials the final was bypassed. To avoid this error, the thermometer was carefully monitored for more accurate results. Based on the data obtained from this investigation, it would be possible to determine the of the morning cup of coffee without the proper thermometer. Also, one could determine if their hot water heater is working properly as well. The data was used to determine the average of the hot water to be 78.9 o C. By using cold water and a thermometer that only went as high as 40.0 o C, the of the hot water could be calculated by using the specific heat equations. The hot water should have been 84.3 o C and the average of the hot water from this investigation was determined to be 78.9 o C. The percent error in the investigation was 6.41%. The error could be caused by several items. These could be the heat loss by moving too slowly, not allowing the ice to melt completely into the cold water, and waiting too long to take the final. The outcome for this investigation was to determine the of the hot water by using a thermometer that only went as high as 40.0 o C. Based on the data that the of the hot water was 78.9 o C and the low percent error of 6.41% this has been accomplished. In future trials of this same investigation it would be best to have all necessary equipment ready and close at hand, work effectively as a group, and not allow as much heat loss. Other refinements could include having a better-built calorimeter.