Freezing and Melting Point of Pure Water
- 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.
- 250 mL beaker
- test tube
- thermometer or temperature probe
- stirring rod
- crushed ice
- distilled water
Part 1: Freezing point of water.
- Fill a 400 mL beaker 1/3 full with ice, then add 100 mL of water.
- 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.
- Place a thermometer into the water inside the test tube.
- When everything is ready, prepare your timer.
- Begin taking the temperatures of the water inside the test tube each 10 seconds.
- 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.
- 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.
- 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.
- Add more ice cubes to the beaker as the original ice cubes get smaller.
- Continue recording the temperature until it reaches around -10°C
Part 2: Melting point of water.
- Raise the test tube and fasten it in a position above the ice-water bath. Do not move the Thermometer during Part II.
- Dispose of the ice water as directed by your teacher.
- Obtain 250 mL of warm tap water in the beaker.
- Begin recording the temperature again, every 10 seconds.
- at 2 minutes lower the test tube and its contents into this warm-water bath.
- Continue recording temperatures until it reaches around 15°C.
- When data collection is complete,
- Graph of temperature vs. time for the freezing and melting point.
- Plot the freezing data with blue and the melting data with red.
|FREEZING POINT OF WATER (part 1)||MELTING POINT OF WATER (part 2)|
- What happened to the water temperature during freezing?
- What happened to the water temperature During melting?
- According to your data and graph, what is the freezing temperature of water?
- According to your data and graph, what is the the melting temperature?
- How does the freezing temperature of water compare to its melting temperature?
- 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.
- Be sure to indicate the freezing temperature on the graph.
- Using another color, draw a melting curve for naphthalene on the same graph.
- Indicate the melting temperature on the curve.
- How you can tell if the substances are pure or contaminated?
Your lab report should show:
- DATA TABLE
- 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|