MnSTEP Teaching Activity Collection > MnSTEP Activities > Growing Crystals--Physical and Chemical changes

Growing Crystals--Physical and Chemical changes

Annette Walen Hokanson, Edinbrook Elementary, Brooklyn Park, MN based on an experiment found on Mrs. Stewart's Bluing website and the 4th grade Chemistry science kit put together by District 279.
Author Profile

Summary

In this chemistry lab, students will conduct a controlled experiment resulting in the growth of salt crystals. They will use their skills of observation to document what goes into the experiment and what comes out, and what they have learned of physical and chemical changes to explain the results.

Learning Goals

This activity is designed for students to conduct a controlled experiment and develop skills of observation and questioning. Students will familiarize themselves with the concepts of evaporation and absorption, physical changes and chemical changes.

Context for Use

This activity can be done with the whole class in pairs or small groups. It is a lab that will involve observations over a period of 2-4 days.

Subject: Chemistry
Resource Type: Activities:Lab Activity
Grade Level: Intermediate (3-5)

Description and Teaching Materials

Magic Crystals
Materials:
- Charcoal Briquettes (or pieces of sponge or brick or porous rock)
- Water
- Salt
- Ammonia
- Bluing
- Food Coloring
- Shallow glass or plastic bowl
- Measuring Spoons
- Empty Jar or cup
Students should have a basic understanding of the terms evaporation, absorption, and what constitutes a physical change versus a chemical change. Before the lab, students should observe the salt crystals under a magnifying glass and draw what they see. After all the ingredients are added, they should again document their observations in their journals regarding what they see in the bowl. This process should be repeated after the crystals grow, and the crystals should be examined under a magnifying glass again.
- In a glass or plastic bowl, put some pieces of coal, coke (charcoal-like substance) charcoal, porous brick, tile, cement or sponge (charcoal tends to create the most dramatic results).
- In the empty jar or cup, pour two tablespoons of water, two of table salt (iodized or plain) and two of Mrs. Stewart's Bluing. Add 2 tablespoons of ammonia to aid the evaporation process, thus quickening the formation of crystals. Add a few drops of food coloring. Stir until salt is mostly dissolved, then spoon mixture over charcoal. Set the bowl aside for at least 1 day. You may also continue with Day 2 and Day 3 additions, but they are not necessary for crystals to grow.
- Day 2: Add two more tablespoons of salt.
- Day 3: Pour into the bottom of the bowl (not directly on the base material) two tablespoons each of salt, water, and Mrs. Stewart's Bluing, and then add a few drops of food coloring or ink to each piece.
- By this time, a beautiful flower-like growth should have appeared. If all the conditions are not ideal, it may be necessary to add two more tablespoons of household ammonia to aid the growth. A free circulation of air is necessary, and these formations will develop better where the air is dry.
- To keep it growing: Add more bluing, salt and water from time to time. It will "bloom" indefinitely into beautiful rosebuds, coral and crystal.

Teaching Notes and Tips

You will need a safe place for these bowls to sit undisturbed. The crystals are fragile and will turn to powder when touched.

Assessment

Students will describe their observations in their journals and write reasons why the crysals are a physical, not chemical, change.

Standards

GRADE 4 I. HISTORY AND NATURE OF SCIENCE
B. Scientific Inquiry
The student will participate in a controlled scientific investigation.
2. The student will collect, organize, analyze and present data from a controlled experiment.
GRADE 4 I. HISTORY AND. NATURE OF SCIENCE.
A. Scientific World
The student will be able to describe physical and chemical changes in matter.

References and Resources

See more MnSTEP Activities »