Beacon Lesson Plan Library

Scientific Method and Crystal Growth

Paul Baldauf PhD

Description

Students use a hands-on experiment in crystal growth to learn about the nature of science as inquiry. In addition to science as inquiry, the students will learn about mineral crystallization and rates of crystal growth.

Objectives

The student knows that it is important to keep accurate records and descriptions to provide information and clues on causes of discrepancies in repeated experiments.

The student knows that a successful method to explore the natural world is to observe and record, and then analyze and communicate the results.

Materials

-Computer(s) with Internet Access
-Magnifying glasses (1 per group)
-Crystals of salt (ordinary table salt will do)
-Grains of sand (not from the beach but the construction sand variety)
-Powdered alum
-Water
-A small pan
-A wooden spoon
-Food coloring
-Several small jars (1 per group)
-Paper towels
-Measuring rulers

Preparations

1. Download and print the Experiment Activity Sheet and Rubric from the associated file.
2. Make copies of the Experiment Activity Sheet and Rubric for each student.
3. Acquire materials listed above. (See Materials.)
4. Make sure the hot plate can heat the pan to boiling.
5. Identify areas in the classroom where open jars of liquid can be safely stored.
6. Prepare computers for Internet research.

Procedures

NOTE: Please notice that three days are required between Day 2 and Day 3 of the lesson plan procedures in order to allow crystals to grow.

Day 1
1. Explain the concept of minerals to the students. Students need to know the definition of a mineral, the difference between minerals and elements, and how minerals grow.

2. Ask the students to get online and do research about diamonds to learn more about minerals and mineral formation. (See WebLinks.)

3. Divide the class into small groups for brainstorming and the hands-on experiments.

4. Have the students brainstorm questions about minerals that they would like to answer. Guide them toward questions about shape, hardness, and crystallization.

5. Collect the questions raised by the groups.

6. Hand out a magnifying glass, along with grains of salt and sand, to each group and ask the students to look at the grains of salt and sand. Students should make observations about the size and the shape of the salt grains. Students should compare the shapes of the salt grains with the shapes of the sand grains. Have the students make sketches of both. Ask them to hypothesize why the grain shapes are different.

7. Ask the students to go home and look for things around the house that are made of minerals. They should bring a list of household products that are made of minerals to class.

Day 2

1. Discuss with the students the results of their home assignments.

2. Explain the concepts of crystallization to the students. The explanation should include the point that many minerals form from the cooling of completely melted materials, such as lava or magma. Many minerals form from the crystallization of substances dissolved in water.

3. Pass out the Experiment Activity Sheet and Rubric to each student. Explain the experiment and how it will be assessed to the students.

4. After explaining the experiment to the students, ask the students to think about what might make the crystals grow larger. Have them think of the variables that could be changed in order to test their hypotheses. Things that could be easily modified are the ratios of alum to water and the position of the evaporation jar. Assign the different groups to test different variations on the experiment. At the end of the experiment, the groups will measure the size of the crystals and compare their results with the other groups.

5. Begin the experiment in crystallization. Gather items 5 through 12 in the Materials list. Each group identified on Day 1 should have a jar with which to work.

6. The teacher should handle the next steps that involve mixing materials and working with the stove. First, measure 4 teaspoons of water and 3 teaspoons of alum into a saucepan on a hot plate.

7. Add food coloring to the mixture.

8. Bring mixture to a boil and stir until the alum is completely dissolved.

9. Allow mixture to cool two minutes. Carefully pour mixture into jar and let sit uncovered for three days. Crystals will form over a three-day period.

10. Ask the students to identify different areas of the room where the jars should be stored in a way that might cause the crystals to be larger or smaller. Ask them to record their expectations in advance on the Experiment Activity Sheet.
(By the end of Day 2, students should have completed #1 and #2 on the Experiment Activity Sheet.)

Day 3
1. After three days, carefully pour off the excess water and spread the crystals on a towel.

2. Ask the students to make sketches of the shapes of the crystals. Ask them to measure the size using rulers. Get them to compare crystals with groups around them. Are they the same size and shape? Ask them to speculate on the results of the experiment. Students should record all observations on the Experiment Activity Sheet.

3. At the end of the lesson, collect Experiment Activity Sheets from all students. (See Assessment.)

Assessments

Collect the Experiment Activity Sheet and use the Assessment Rubric in the attached file to formatively assess the Experiment Activity Sheet. This lesson is designed to help the students begin to understand the concepts of scientific inquiry, especially hypothesis building and scientific method. The lesson should be judged primarily on how well the students did in the hypothesis and results areas of the Experiment Activity Sheet.

Circulate and formatively assess students as they use the technology tools. Provide assistance for students who are experiencing difficulty and monitor accordingly.

Extensions

The lesson could be extended to include more information about minerals. For example, the teacher could spend an hour discussing mineral hardness. The students could scratch different minerals with common tools or against other minerals to determine relative hardness. This could be done in the context of a lesson about earth materials or could be used as an extension of the scientific method. Instead of telling the students how to determine hardness, they could be given the tools, told that their goal is to say something about the hardness of the tools and minerals, and then they could list their expectations in advance of experimentation.

Another approach might be to make this into a detective themed assignment. Using a mystery or a crime that needed to be solved could reinforce the theme of scientific inquiry.

Web Links

Web supplement for Scientific Method and Crystal Growth
A World of Diamonds

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