HeatingandCoolin...

Name:__________________
Heating and Cooling Curve of a Pure Substance
Objective:
To distinguish between substances based on melting and freezing points. In this lab, two substances will be provided in their frozen state. The objective of the lab is to use temperature data (in Celcius) to determine if the substance is Lauric or Stearic Acid.
Materials:
Ring Stand Beaker (400 mL)
Buret Clamp Thermometer for water bath
Hot Plate Lauric Acid
Test Tube Stop Watches
Safety Goggles Stearic Acid
Pre Lab: Before completing the pre lab, read over the lab procedures. Froggers should be ready to start this lab immediately.
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1. Define melting point and freezing point.
2. Describe what happens to the particles of a solid at its melting point. Draw a diagram.
3. Describe what happens to the particles of a solid at its freezing point. Draw a diagram.
4. What precautions need to be taken in this investigation?
5. What is the freezing and the melting point of Lauric Acid?
6. What is the Chemical formula of Lauric Acid?
7. What products are made with Lauric Acid?
8. What is the freezing and the melting point of Stearic Acid?
9. What is the chemical formula of Stearic Acid?
10. What products are made with Stearic Acid?
11. What steps have to be taken at the end of the heating process?
12. What do you have to be ready to do immediately when you start the cooling process?
Procedure:
Part I: The Heating Process
1.Put on your safety goggles.
2.With your partner, decide in advance the role each of you will perform in Part I.
Role #1 : One partner will act as the observer. The observer will be responsible for
reading the thermometer.
Role #2: One partner will act as the recorder, asking the observer the temperature at 30
second intervals.
3.Put 300 mL of water in a 400 mL beaker and place the beaker on the hot plate. Turn the hot plate
on to high heat and raise the temperature of the water bath to between 55°C and 60°C (use a
thermometer to take the temperature). Monitor the water temperature with a thermometer.
4.When the water has reached 55°C turn the hot plate to medium heat. Lower the test tubes using
clamps into the water bath and clamp it in position so that test tube is submerged below the water line.
5.Record the temperature of the red and yellow labeled substances in your copy of Table 1, at the
beginning and every 30 seconds after that.
6.Temperature readings should continue to be taken every 30 seconds, until the acid completely
turns to a liquid.
7.Turn off the hot plate and move quickly to Part II.
Part II: The Cooling Process
1.Part II, like Part I, requires teamwork. You will switch roles for part two.
Role #1 : One partner will act as the observer. The observer will be responsible for reading the
thermometer.
Role #2: One partner will act as the recorder, asking the observer the temperature at 30 second
intervals.
2.Remove the beaker of water from beneath the test tube. The beaker will be hot, so use tongs
with rubber grips.
3.Immediately start monitoring the cooling process.
4.Record the temperature of the samples every 30 seconds until a temperature near 25°C is attained.
5.When a temperature at or near 25°C has been attained you may stop recording temperature
readings.
6.Set the lab back up the way you found it. A beaker of water should go back on the hot plate.
7.Wash your hands thoroughly with soap and water.
Analysis of Results:
Construct a graph for Lauric Acid:
ing the data you obtained, for Lauric Acid, during the heating process, construct a line graph
of temperature (y axis) versus time (x axis). Use shaded points to indicate the heating points.
2. Draw a smooth curve through the plotted points using a pencil.
3.On the same graph as the heating curve, plot temperature versus time for the cooling process.
Use non-shaded circles to indicate the cooling points.
4.Make sure to include a legend that tells which points are the heating curve and which points are
the cooling curve points!
5.What is the temperature of the flattest part (plateau) of the Cooling Curve? ________ This is the
freezing point.
6.What is the temperature of the flattest part (plateau) of the Heating Curve? _______ This is the
Melting point.
Construct a graph for Stearic Acid:
ing the data you obtained, for Stearic Acid, during the heating process, construct a line graph
of temperature (y axis) versus time (x axis). Use shaded points to indicate the heating points.
2. Draw a smooth curve through the plotted points using a pencil.
3.On the same graph as the heating curve, plot temperature versus time for the cooling process.
Use non-shaded circles to indicate the cooling points.
4.Make sure to include a legend that tells which points are the heating curve and which points are
the cooling curve points!
5.What is the temperature of the flattest part (plateau) of the Cooling Curve? ________ This is the
freezing point.
6.What is the temperature of the flattest part (plateau) of the Heating Curve? _______ This is the
Melting point.。