CHEMISTRY NOW: Density Comparison of Water and Ice (Grades 5-8) Print

Objective:

Students will be able to describe the density of water as a liquid and a solid. Students will conduct an experiment that visually demonstrates the density of water and ice. Students will be able to calculate the density of water and ice


Introduction Notes:

CHEMISTRY NOW: Density Comparison of Water and Ice

 

Subject Area: Chemistry

Grade Level:  Middle School Chemistry

Lesson Title: Density Comparison of Water and Ice

National Science Standards:

Science as Inquiry: 5-8

Science as Inquiry: 9-12

 

Physical Science Standards:

properties and changes of properties: 5-8

structure of atoms: 9-12

structure and properties of matter: 9-12

chemical reactions: 9-12

 

Suggested Prior Knowledge: concepts and relationships of mass, volume, and temperature

Purpose: To give students an understanding of water’s density as a liquid and solid

Key Vocabulary:

freezing point- the temperature at which a substance turns from a liquid into a solid; water is different from nearly all other substances because it is densest in liquid form at about 4 o C., less dense in solid form at 0 o

hydrogen bonds- weak bonds that form between small molecules, specifically involving an atom that has a partial negative charge, especially oxygen in water and in living things, and another atom (such as hydrogen) having a partial positive charge; results in 'sticking together' of molecules

polarity - possessing two opposed poles; a characteristic of molecules which have unequal distributions of charge; water is polar because the oxygen has a partial negative charge and the hydrogen atoms each have a partial positive charge; polar molecules interact with other polar and charged molecules and ions.

density - Density of a material is defined as its mass per unit volume.

Objectives:

  1. Students will be able to describe the density of water as a liquid and a solid
  2. Students will conduct an experiment that visually demonstrates the density of water and ice
  3. Students will be able to calculate the density of water and ice

Materials: insulated gloves as needed, plastic 100ml graduated cylinder, freezer, distilled water, hot plate, 200ml beaker, beaker tongs, pipette, safety goggles.

Procedure: ­

1. Discuss with students how we can design an experiment that allows us to examine the density of water or ice. Lead the students towards a technically correct experiment that would yield accurate results. As the students develop the procedure, the teacher should validate and prioritize their answers in order to create a valid procedure similar to the one in this lesson plan. Begin with a leading question and follow-up:

 

         What is the difference between water and ice?

         What can water do that ice cannot?

         What does density measure?

         What kind of experiment can we do to find the density of water and ice?

 

2. Lab safety equipment and protocols should be followed. The following can be completed as a teacher demonstration or as a class experiment:

 

3.  Record the dry mass of the plastic graduated cylinder.

 

4.  This experiment works best with water that is free of dissolved oxygen or minerals. By using water that is distilled and free of oxygen your ice will be clear and easier to read its volume when frozen.

 

     For this, boil approximately 100ml of distilled water for 2-3 minutes in a 200ml beaker to remove most of the oxygen from the solution.

 

5. Then, using your beaker tongs, transfer the hot liquid to a plastic graduated cylinder to exactly 50ml (note: a glass graduated cylinder may rupture). If necessary, use a pipette to transfer hot water as required to ensure accuracy.

 

6. Place the cylinder with 50ml of hot water in a freezer until completely frozen solid (several hours). Your ice will be clear.

 

7. Remove the beaker from the freezer and record the volume of ice.

 

8. Have the students record the data and calculations from this experiment.

 

9. Have students calculate the density of both ice and water. (D=M/V) (ice=0.92 g/ml, water =1.0 g/ml)

 

10.  Have students draw a conclusion about the properties of water vs. ice.

 

11. After the students have drawn conclusions regarding the volume and density of water in liquid and solid form, finish the discussion as to why ice has a greater volume than water. The molecular diagram of ice below can be used to show how the hydrogen bonds are equidistant from their neighboring water molecule. The concept of polarity of water can be introduced to explain why the volume of ice is greater than water in the experiment.

 

Additional Resources:

http://www.lpi.usra.edu/education/explore/ice/background/allAboutWater/index.shtml

http://www.chem1.com/acad/sci/aboutwater.html

http://www.middleschoolchemistry.com/multimedia/chapter2/lesson2#models_of_water_molecules

 

 

 

 

 

 

 

 

 

Student Worksheet for Density Comparison of Water and Ice

 

 

Experiment Title: ______________________Date: __________Name: _____________

 

Student Hypothesis: _____________________________________________________

 

Materials: _____________________________________________________________

 

Procedure: ___________________________________________________________

  1. ___________________________________________________________________
  2. ___________________________________________________________________
  3. ___________________________________________________________________
  4. ___________________________________________________________________
  5. ___________________________________________________________________
  6. ___________________________________________________________________

 

 

Data:

 

Graduated cylinder (grams)

 

Graduated cylinder + water (grams)

 

Graduated cylinder + ice (grams)

 

Mass of water (grams)

 

Volume water (ml)

 

Mass of Ice (grams)

 

Volume ice (ml)

 

Results:

 

Density of Ice

 

Density of Water

 

 

Observations: 

  1. ___________________________________________________________________

 

  1. ___________________________________________________________________

 

  1. ___________________________________________________________________

 

 

Conclusion: ______________________________________________________________

 

________________________________________________________________________

 

 

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