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Learning Aim: Undertake Calorimetry to Study Cooling Curves
Calorimetry is the scientific process used to measure the heat released or absorbed during a chemical reaction. By quantifying the heat change, we can determine whether a reaction is exothermic (heat-releasing) or endothermic (heat-absorbing) 1.
The term "calorimetry" derives from the Latin word "calor" meaning heat, and the Greek word "metron" for measure.
Calibration involves aligning the readings of an instrument with those of a known standard to assess its accuracy.
It is essential in scientific research to ensure the reliability of data. Accuracy refers to how closely the measured value matches the actual value 2.
Scientific instruments, including thermometers, can become inaccurate over time due to factors such as aging and usage.
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This inaccuracy, often referred to as "drift," can lead to unreliable results.
This section covers the equipment used, risk assessment, and the setup for calibrating both digital and liquid thermometers safely.
| Hazard | Risk | Precaution |
|---|---|---|
| Boiling Water | Could burn skin | Leave adequate time for wire gauze to cool down |
| Hot Wire Gauze | Could burn hair | Tie hair back if hair is long |
| Bunsen Burner | Could burn skin and/or eyes | Wear goggles and be mindful when handling the boiling water |
The calibration process involves two methods: boiling water calibration and ice bath calibration, each using a different known standard for calibration.
1. Place the digital scale on a level platform for accuracy.
Turn it on and weigh the graduated measuring cylinder, recording the result. This measurement will be used to subtract the cylinder's mass from that of the water and cylinder combined.
2. Fill the measuring cylinder with 150ml of water, weigh it, and record the result. This step determines the mass of the water, ensuring that a similar mass of ice is used later to minimize inaccuracies.
3. Subtract the recorded mass of the empty cylinder from the combined mass of the cylinder and water. This provides the mass of water in grams.
4. Set up the Bunsen burner, connect it to a gas supply via the rubber tube, and place it on a heatproof mat under the tripod stand. Place the wire gauze on the tripod stand to ensure stability and safety.
5. Pour the water from the graduated measuring cylinder into the beaker and place the beaker on the wire gauze above the Bunsen burner. Turn the Bunsen burner collar to fully cover the air hole, producing a safety flame that confirms the burner is on but not being used for heating.
6. Insert the analog thermometer into the beaker and open the Bunsen burner collar to increase air flow, resulting in a hotter flame with complete combustion.
7. Wait for the water to start boiling and check if the analog thermometer reads 100 degrees Celsius. Record the thermometer reading and replace it with the digital thermometer to compare the readings.
8. Repeat the process of swapping and allowing the thermometers to cool three times. Calculate the mean of the results for each thermometer. This repetition under consistent conditions helps estimate result variability and improve accuracy, assuming no systematic errors are present.
1. Calculate the mass of the water and measuring cylinder by subtracting the previously recorded mass of the empty cylinder (107g) from the combined mass of the 150ml water and cylinder (260g), resulting in a mass of 153g.
2. Empty the ice cubes into a beaker and add cool water. Stir the ice bath well using a glass rod and wait for 30 seconds to ensure temperature equilibrium.
3. Submerge the thermometers into the ice bath at three intervals, swapping between the two thermometers each time a stable reading is recorded. Ensure the bulb of the liquid thermometer or the tip of the digital thermometer is surrounded by ice cubes and positioned in the middle of the ice bath. This procedure ensures accuracy and measures the temperature of the ice bath, which remains a known constant at 0 degrees Celsius, used for calibrating the thermometers.
| Thermometer and Trial | Reading in Degrees Celsius |
|---|---|
| Liquid Analogue 1 | 104 |
| Liquid Analogue 2 | 103 |
| Liquid Analogue 3 | 105 |
Mean reading = 104 Degrees Celsius
| Thermometer and Trial | Reading in Degrees Celsius |
|---|---|
| Digital 1 | 100.6 |
| Digital 2 | 100.6 |
| Digital 3 | 100.5 |
Mean Reading = 100.57 Degrees Celsius
| Thermometer and Trial | Reading in Degrees Celsius |
|---|---|
| Liquid Analogue 1 | 1 |
| Liquid Analogue 2 | 1 |
| Liquid Analogue 3 | 2 |
Mean reading = 1.33 Degrees Celsius
| Thermometer and Trial | Reading in Degrees Celsius |
|---|---|
| Digital 1 | 0.6 |
| Digital 2 | 0.5 |
| Digital 3 | 0.6 |
Mean Reading = 0.566 Degrees Celsius
In conclusion, the liquid thermometer has an average deviation of 1.33 degrees Celsius, while the digital thermometer has an average deviation of 0.566 degrees Celsius. This indicates that the digital thermometer is more accurate. Therefore, I will use the digital thermometer to record temperature data for my experiment, ensuring greater precision and reliability in the results.
This section outlines the equipment, risk assessment, and the setup for generating a time-temperature data table and a graph depicting temperature against time for the cooling of Paraffin wax.
| Hazard | Risk | Precaution |
|---|---|---|
| Boiling Water | Could burn skin | Leave adequate time for wire gauze to cool down |
| Hot Wire Gauze | Could burn hair | Tie hair back if hair is long |
| Bunsen Burner | Could burn skin and/or eyes | Wear goggles and be mindful when handling the boiling water |
Below is a table presenting time-temperature data for the cooling of Paraffin wax:
| Time in Minutes | Temperature in Degrees Celsius |
|---|---|
| 00:00 | 87.4 |
| 00:30 | 84.6 |
| 01:00 | 80.0 |
| 01:30 | 75.8 |
| 02:00 | 73.6 |
| 02:30 | 69.9 |
| 03:00 | 66.4 |
| 03:30 | 63.5 |
| 04:00 | 60.7 |
| 04:30 | 58.5 |
| 05:00 | 57.8 |
| 05:30 | 55.5 |
| 06:00 | 53.8 |
| 06:30 | 52.9 |
| 07:00 | 51.5 |
| 07:30 | 50.3 |
| 08:00 | 49.3 |
| 08:30 | 48.4 |
| 09:00 | 46.6 |
| 09:30 | 46.0 |
| 10:00 | 45.6 |
| 10:30 | 44.6 |
| 11:00 | 44.1 |
| 11:30 | 43.4 |
| 12:00 | 43.8 |
| 12:30 | 42.4 |
| 13:00 | 42.1 |
| 13:30 | 41.7 |
| 14:00 | 41.3 |
| 14:30 | 41.1 |
| 15:00 | 40.9 |
| 15:30 | 40.6 |
| 16:00 | 40.2 |
| 16:30 | 39.6 |
| 17:00 | 38.7 |
| 17:30 | 38.2 |
| 18:00 | 38.2 |
| 18:30 | 38.2 |
| 19:00 | 37.9 |
| 19:30 | 37.7 |
| 20:00 | 36.3 |
| 20:30 | 35.9 |
| 21:00 | 35.5 |
| 21:30 | 35.3 |
| 22:00 | 35.0 |
| 22:30 | 34.8 |
| 23:00 | 31.6 |
| 23:30 | 30.8 |
| 24:00 | 30.5 |
Rate of Cooling:
The rate of cooling is determined by plotting a temperature versus time graph and drawing a cooling rate curve. To find the rate of cooling, we draw a tangent to the curve at specific points: Triangle A, representing the rapid temperature decrease during Paraffin wax's liquid cooling phase; Triangle B, where the temperature remains approximately constant, known as "thermal arrest"; and Triangle C, indicating the slope during solid cooling.
Cooling Curves:
Cooling curves are graphical representations depicting temperature changes over time. The initial point on the graph represents the starting temperature of the substance, which, in this case, is 87 degrees Celsius for Paraffin wax. The points where the graph plateaus indicate "thermal arrest," signifying a change in state – in this context, freezing. During this phase, the substance transitions from a solid to a liquid as it loses thermal energy, and intermolecular bonds strengthen with particles vibrating less.
This section details the equipment, risk assessment, and setup for creating a table and a graph illustrating temperature changes over time for the cooling of Stearic Acid.
| Hazard | Risk | Precaution |
|---|---|---|
| Boiling Water | Could burn skin | Leave adequate time for wire gauze to cool down |
| Hot Wire Gauze | Could burn hair | Tie hair back if hair is long |
| Bunsen Burner | Could burn skin and/or eyes | Wear goggles and be mindful when handling boiling water |
Here is the table presenting time-temperature data for the cooling of Stearic acid:
| Time in Minutes | Temperature in Degrees Celsius |
|---|---|
| 00:00 | 93.5 |
| 00:30 | 93.3 |
| 01:00 | 93.3 |
| 01:30 | 89.8 |
| 02:00 | 86.3 |
| 02:30 | 85.3 |
| 03:00 | 78.7 |
| 03:30 | 74.8 |
| 04:00 | 72.2 |
| 04:30 | 69.5 |
| 05:00 | 66.7 |
| 05:30 | 64.5 |
| 06:00 | 62.6 |
| 06:30 | 60.5 |
| 07:00 | 58.6 |
| 07:30 | 56.8 |
| 08:00 | 55.6 |
| 08:30 | 54.8 |
| 09:00 | 54.5 |
| 09:30 | 54.2 |
| 10:00 | 54.9 |
| 10:30 | 53.8 |
| 11:00 | 53.5 |
| 11:30 | 53.3 |
| 12:00 | 53.3 |
| 12:30 | 53.1 |
| 13:00 | 53.0 |
| 13:30 | 52.9 |
| 14:00 | 52.7 |
| 14:30 | 52.5 |
| 15:00 | 52.5 |
| 15:30 | 52.2 |
| 16:00 | 52.1 |
| 16:30 | 52.0 |
| 17:00 | 51.9 |
| 17:30 | 51.7 |
| 18:00 | 50.0 |
| 18:30 | 49.7 |
| 19:00 | 49.3 |
Rate of Cooling:
Calculating the rate of cooling involves examining the temperature changes at specific points: liquid cooling (A), thermal arrest (B), and solid cooling (C) for Stearic acid.
How the Rate of Cooling Relates to Intermolecular Forces and the State of the Substance:
During the setup phase, Paraffin wax is observed as a solid. When heat is applied, it undergoes a phase change known as melting. This process occurs as the internal energy of the solid increases, causing the particles within the substance to gain energy and vibrate more rapidly. Initially, this weakening of the bonds makes the wax "softer." Continued heating eventually provides enough energy to disrupt the Paraffin wax's structure, allowing the particles to break free from the intermolecular forces of attraction. This specific point is referred to as the melting point.
Upon allowing the liquid to rest, it gains viscosity and eventually solidifies, a process called freezing. This transformation occurs as energy is lost to the surroundings, causing the particles to lose energy and vibrate less.
These observations align with the principles of the particle model, a scientific theory that explains the properties of solids, liquids, gases, and their response to temperature changes (thermal energy).
In this section, I will evaluate the accuracy of the practical work conducted in calorimetry, specifically in relation to the analysis of the cooling curve.
Personal Competencies and Skill Evaluation in My Method:
One practical skill I improved upon in my method is zeroing the scale and ensuring it is placed on a level surface before measuring the mass of the stearic acid. This step helps maintain accuracy by excluding variables like the weighing boat's mass from the measurement.
However, one aspect I could have executed better is calibrating the scale by pressing the CAL button and using a calibrating weight. This additional step could have further enhanced the accuracy of my method.
Feedback Received from Peers and How It Aided My Method:
During the calibration of the liquid thermometer, a classmate pointed out that I did not ensure the measuring bulb was positioned at the center of the beaker filled with hot water. Instead, it was sitting at the bottom, unsecured by a clamp, with the bulb on the far-right side of the beaker. Upon receiving this feedback, I promptly repeated the boiling water calibration of my thermometer, rectifying the mistake and ensuring the accuracy of the calibration.
Analysis of My Results:
While my results were similar to those of my peers, I could have conducted further research on the rate of cooling for the substances online and compared my results to those collected by others. This additional step would have provided a better understanding of the representativeness of my results.
Calorimetry and Calibration Lab: Heat Measurement & Instrument Precision. (2024, Jan 11). Retrieved from https://studymoose.com/document/calorimetry-and-calibration-lab-heat-measurement-instrument-precision
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