Analía Bellizzi – Chemistry Classes

Ronald Reagan High School

Freezing and Melting point of water

Freezing and Melting Point of Pure Water

Introduction:

    • Freezing Point is the temperature at which a substance turns from a liquid to a solid.
    • Melting Point is the temperature at which a substance turns from a solid to a liquid.
    • Freezing temperature and melting temperature are characteristic properties of a pure substance.
    • When heating up a solid, its particles will increase their kinetic energy, which can be measure by an increase in the temperature.
    • At the melting point, the applied heat will be used to change the state of the matter from solid to liquid, so while it is changing state, there will not be a change in temperature.

Purpose of the lab:

Determine the relationship between the freezing and melting temperatures of water.

 Materials

    • 250 mL beaker
    • test tube
    • thermometer or temperature probe
    • stirring rod
    • crushed ice
    • salt
    • timer
    • distilled water

Procedure

Part 1: Freezing point of water. 

    1. Fill a 400 mL beaker 1/3 full with ice, then add 100 mL of water.
    2. Put 2 mL of distilled water into a test tube and use a utility clamp to fasten the test tube to a ring stand.The test tube should be situated above the water bath.
    3. Place a thermometer into the water inside the test tube.
    4. When everything is ready, prepare your timer.
    5. Begin taking the temperatures of the water inside the test tube each 10 seconds.
    6. After 2 measurements, lower the test tube into the ice-water bath.
      IMPORTANT: Keep the test tube submerged in the ice-water bath all the time.
      Keep the thermometer in the test tube all the time!. do not take it out for reading.
    7. Soon after lowering the test tube, add 5 spoons of salt to the beaker and stir with a stirring rod.
      Continue to stir the ice-water bath during Part I.
    8. Slightly, but continuously, move the thermometer during the first 5 minutes of Part I. Be careful to keep the thermometer in, and not above, the ice as it forms. After a few minutes, do not move the thermometer anymore. Allow it to freeze into the ice.
    9. Add more ice cubes to the beaker as the original ice cubes get smaller.
    10. Continue recording the temperature until it reaches around -10°C

Part 2: Melting point of water. 

    1.  Raise the test tube and fasten it in a position above the ice-water bath. Do not move the Thermometer during Part II.
    2. Dispose of the ice water as directed by your teacher.
    3. Obtain 250 mL of warm tap water in the beaker.
    4. Begin recording the temperature again, every 10 seconds.
    5. at 2 minutes lower the test tube and its contents into this warm-water bath.
    6. Continue recording temperatures until it reaches around 15°C.
    7. When data collection is complete,
    8. Graph of temperature vs. time for the freezing and melting point.
    9. Plot the freezing data with blue and the melting data with red.

Data Table

FREEZING POINT OF WATER (part 1)   MELTING POINT OF WATER (part 2)
time 
(sec)
Temp
 (ºC)
  time 
(sec)
Temp
 (ºC)
0:00 0:00
0:10 0:10
0:20 0:20
0:30 0:30
0:40 0:40
0:50 0:50
1:00 1:00
1:10 1:10
1:20 1:20
1:30 1:30
1:40 1:40
1:50 1:50
2:00 2:00
2:10 2:10
2:20 2:20
2:30 2:30
2:40 2:40
2:50 2:50
3:00 3:00
3:10 3:10
3:20 3:20
3:30 3:30
3:40 3:40
3:50 3:50
4:00 4:00
4:10 4:10
4:20 4:20
4:30 4:30
4:40 4:40
4:50 4:50
5:00 5:00
5:10 5:10
5:20 5:20
5:30 5:30

Analysis Questions:

  1. What happened to the water temperature during freezing?
  2. What happened to the water temperature During melting?
  3. According to your data and graph, what is the freezing temperature of water?
  4. According to your data and graph, what is the the melting temperature?
  5. How does the freezing temperature of water compare to its melting temperature?
  6. Naphthalene, (moth balls) has a freezing temperature of 80.26°C. By using a similar line graph to the one built for the water, sketch and label a freezing curve for naphthalene.
  7. Be sure to indicate the freezing temperature on the graph.
  8. Using another color, draw a melting curve for naphthalene on the same graph.
  9. Indicate the melting temperature on the curve.
  10. How you can tell if the substances are pure or contaminated?



Your lab report should show:

  • TITLE
  • PURPOSE
  • MATERIALS
  • PROCEDURE
  • DATA TABLE
  • GRAPH
  • ANALYSIS QUESTIONS

If you were absent for the lab, you can use the following data table to build your lab report and graph.

FREEZING POINT OF WATER MELTING POINT OF WATER
time
(sec)
Temp
(ºC)
time
(sec)
Temp
(ºC)
0:00 23 0:00 -5
0:10 19 0:10 -2
0:20 15 0:20 -1
0:30 10 0:30 -1
0:40 7 0:40 0
0:50 4 0:50 0
1:00 3 1:00 0
1:10 2 1:10 0
1:20 2 1:20 0
1:30 1 1:30 0
1:40 1 1:40 1
1:50 1 1:50 1.5
2:00 0 2:00 2
2:10 0 2:10 2.5
2:20 0 2:20 3
2:30 0 2:30 3.5
2:40 0 2:40 4
2:50 0 2:50 4
3:00 0 3:00 4.5
3:10 0 3:10 4.5
3:20 0 3:20 5
3:30 -0.5 3:30 6
3:40 -1 3:40 7
3:50 -2 3:50 8
4:00 -2 4:00 10
4:10 -3 4:10 11
4:20 -4 4:20 13
4:30 -6 4:30 14
4:40 -9 4:40 16
4:50 -10 4:50 17
5:00 -10 5:00 19
5:10 -11 5:10 20
5:20 -12 5:20 22
5:30 -12 5:30 23