LAB: PHASE CHANGES
Elizabeth Craig
Chemistry, 10th –12th
Gretna High School
Goal of the Lesson: To utilize the Vernier temperature probe and Vernier Probe ware
Logger Pro software to obtain the freezing and melting point of a
substance.
SOL addressed:
SOL CH 1- The student will investigate and understand that
experiments in which variables are measured, analyzed, and
evaluated, produce observations and verifiable data.
SOL CH.5- The student will investigate and understand that the
phases of matter are explained by kinetic theory and forces of
attraction between particles.
Objectives of the lesson:
After completing this experiment, the student should be
able to examine the data obtained by the Vernier
temperature probe and determine the melting and freezing
point of a substance.
Materials:
Venier Probe ware Logger Pro Software
ring stand
beakers (600mL, 400mL)
striker
buret clamp
wire gauze
Vernier temperature probe
centigram balance
Bunsen burner
iron ring
pyrex test tube (25 X100mm)
acetamide
Procedures:
Part I
1. Place a 600-mL beaker three-fourths full of water on a ring stand and heat the water
to boiling. Also fill a 400-mL beaker three-fourths full of water and set aside for Part
II.
2. While the water is heating, measure 10 grams of acetamide and place in a 25 X 100
mm Pyrex test tube. Clamp the test tube above the hot water bath.
3. Plug in the power cord and plug the temperature probe into CH 1 and start the Logger
Pro software on a Windows computer. Insert the temperature probe into the
acetamide in the test tube and clamp the probe off the bottom of the test tube. Click
on Setup and go to Data Collection to Sampling and change experiment length to 10
minutes and to four samples per minute. You are now ready to collect data.
4. When the water bath begins to boil, reduce the burner to a low flame and click on
Collect and begin collecting data. Immediately immerse the test tube into the hot-
water bath by lowering the buret clamp on the ring stand. The temperature will be
recorded every fifteen seconds allowing the temperature to exceed 900C.
Part II.
5. When the temperature of the acetamide exceeds 900C, turn off the burner. Remove
the test tube from the boiling water and clamp it opposite the hot-water bath.
6. If the temperature drops below 750C without crystallizing, drop a few seed crystals of
acetamide in the liquid.
7. After the first crystals appear in the liquid, immerse the test tube in the cold-water
bath that you prepared in Part I. Continue taking temperature reading until the
acetamide cools below 700C.
8. Stop collecting the data when the temperature cools below 700C regardless of the
time expired.
9. Reheat the solid acetamide in the hot-water bath. When the solid has melted, remove
the temperature probe and dispose of the acetamide as directed by your instructor.
10. Clean all equipment which includes unplugging the temperature probe and returning
it to its’ zip-locked bag.
GRAPH of Collected Data:
Assessment:
(For Students)
Questions:
1.
What is the shape of the part of the graph that represents the cooling of the liquid?
_________________________________________________________________
2.
What is happening to the kinetic energy of the acetamide molecules as the liquid
cools?____________________________________________________________
3.
What happens to the entropy of acetamide as it changes from a liquid to a solid?
__________________________________________________________________
4.
What is the melting temperature of acetamide? ____________________________
5.
What is the freezing temperature of acetamide?____________________________
(For Teachers)
I learned by running different trials that I needed to change the experiment length and the
number of samples taken. The example below demonstrates this since it is impossible to
determine the two flat points on the graph. Other possible trouble areas are caused by
stirring the liquid and allowing the probe to rest on the bottom of the test tube when
recording the temperature.