LAB: Equilibrium and Conservation of Mass in the Global Water Cycle Name:  __________________________       Date:    __________________________

Problem
A perfectly "closed" system is one in which there is no net loss with respect to a specific quantity such as mass or energy.

In this experiment you will create a mini model of the water cycle, and you will see that the water will move to different parts of the system.  You will measure the change in the mass of the system as heat is added (from a hot plate).  What will happen to the total mass of the system when heat energy is added for a period of time?

Your Hypothesis
Make a hypothesis about what will happen to the mass of the water in the mini system over time.
Identify the independent and dependent variables.

Materials
1000 ml beaker
Watch glass
150 ml water
Hot plate - medium high or lower
clock
Beaker tongs
Balance (0.1 gram)
graph paper

Procedure
1.  Make a data table for recording mass every 4 minutes for at least 30 minutes.
2.  Pour 150 ml of room temperature water into the beaker and put the watch glass on top.
3.  Put the beaker on a hot plate and begin to heat it on medium low. (Be careful and patient.  Do not let the water boil hard.)
4.  Use the tongs to carefully set the beaker on the balance every 4 minutes and carefully determine it's mass.  Immediately put it back on the hot plate.
5.  Record time and mass every 4 minutes for at least 30 minutes.
6.  Clean up and return the equipment.
7.  Write a Lab Report.

Procedure
Remember to write your method in the past tense.
Include a labeled sketch of the equipment set up.

Data
Make sure your data table has clear labels and shows units.
Make a line graph showing mass vs time.

Analysis of the Results
    1.  What changes did you observe as the water was heated?
    2.  What causes these changes?
    3.  Explain the shape of your graph.
    4.  Is the mini water cycle an open or closed system with respect to water?
    5.  Account for, and discuss, the uncertainties in your data.

Conclusion
    Restate your hypothesis and evaluate it.  Present the conclusions you reached about the research question.  Make sure to explain how you arrived at these conclusions based on your methodology and data analysis.  Show your reasoning.

Discussion
Put your conclusions in context; what do they mean?  In your discussion use the following key vocabulary words:  mass,  equilibrium,  condensation, evaporation, water vapor, conservation of mass, open system,  closed system.   Include answers to the following questions in your discussion.
(Write a paragraph - Do not write in question/answer format).

    1.  Do you think there was equilibrium in the mini system?  What evidence do you have?
    2.  Was the mass of the water in the mini system conserved? (That means the mass was changed, but none was destroyed.)  How do you account for what happend to every molecule of the water?
    3.  Create a box model of your mini water cycle showing the flow of water.
    4.  List the similarities and differences between the mini model and the global water cycle.  What are the limitations of the mini model?
    5.  Suggest a new question for further study.