Warming and Cooling Curves
Purpose: Graph warming and cooling curves over phase change
Discussion: the phase change can be found on the plateau of the graph. It takes energy to raise temperature; it also takes energy to change liquid to gas (heat of vaporization).Energy must be removed to lower temperature; energy must also be removed to change liquid to solid (heat of fusion)
Procedure: Part 1; Record time and temp (every 0.5 minutes) as water warms from room temp to boiling. Done as a class.
Part 2: Prepare a salt/ice cooling bath in a 250mL beaker, then immerse a small test tube with a thermometer and small amount of water or use temp probe(optional); download logger lite or get program from my cd (When the green play arrow turns red, click on the button again, and an option should show up that says "Append to latest," this should continue the graph. ). Record time and temperature as water cools from near boiling to -10 celsius.
Part 3: Get hot paradichlorobenzene from the instructor. record time and temp as it cools from about 95 celsius to room temp.
Plot all points on the same graph paper; Plot time on x and temp on y, Connect with 3 different color lines. make a key, label axes, etc.
Data.
Part 1 warming water part 2 cooling water part 3 cooling pdb
time(min) | temp time | temp time | temp
0 22 C 0 90C 0 95C
.5
1.0
etc
Plot all sets of data points on the same graph paper; Plot time on x and temp on y, Connect with 3 different color lines. make a key, label axes, etc.
Conclusion:
What was inside the bubbles in the boiling water?
Why couldn't the bubbles be hydrogen and oxygen gas?
What is the boiling point of water? How can you tell from the graph?
Is it possible to heat a substance without its temperature going up? Explain.
How cold will the salt ice mixture get?
Why is salt put on roads in the winter?
Why doesn't salting roads work when it gets too cold?
What is the freezing point of water? How can you tell from the graph?
What is the melting point of water?
label the following for all 3 graphs; initial temp, final temp, freezing pt , melting pt, boiling pt. , state of matter.
1.What is the structure and formula of paradichlorobenzene?
2.What are 2 uses of this chemical?
3.Based on the lab data, What is the freezing point of the paradicholorbezene? How can you tell from the graph?
4. (use internet to for first 2 questions in not in class; use internet to check how close you were for question number 3..... is there a difference? If there is, why do you think there is a difference.)
5. How cold could the pdb get in our lab?
6. which would feel colder, river water at 1degree C, or air at -10degrees C? why?
7. Is it possible to remove heat without the temperature decreasing? Explain.
8. What is the melting pt of pdb?
9. Is energy added or removed when the water changes from liquid to solid? If the heat of fusion of water is 6 kilojoules per mole, and we had about 9 grams of water, how much energy was involved in the freezing?(See sample problem p351e333) rchem may skip this calculation
10. Explain how the concepts of heat of vaporization and fusion are used in the activity of sweating and keeping your soda cool on a hot day with ice.
11. Does energy have to be added or removed to change liquid water to vapor? (See sample problem p351e333) Suppose that 9g of liquid water vaporized while boiling. If the heat of vaporization is 41kilojoules per mole, how much energy was involved in the vaporization?
12. answer sweat question and melting pt. question;