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Crystal Trees and Gardens

Students see dissolved substances come out of prepared solution.

The amount of salt that can dissolve in water depends on the temperature of the water. As water evaporates from a salt and water solution, the salt stays behind and forms crystals.

The solution you make in this activity is a very concentrated salt solution. As soon as the water starts to evaporate, crystals will start to form.

Mrs. Stewart's Bluing is a colloidal suspension of extremely tiny particles of blue powder [ferric hexacyanoferrate]. As the water and ammonia in the solution evaporate, salt crystals form around the tiny blue particles.

The purpose of the charcoal or lava rocks is to soak up the liquid from the muffin tin and spread it out. This speeds up evaporation and causes the crystals to form over a larger area than just the rim of the tin.  

Objectives

  • Describe the general process of crystal formation.

Materials

  • Table salt (plain, not iodized)
    Ammonia solution (regular household ammonia, not sudsy type)
    Laundry bluing (such as Mrs. Stewart’s–available at a grocery store)
    Food colouring
    Blotter paper (for crystal tree) or lava rock or charcoal briquettes (for crystal garden)
    Bottle to hold crystal solution
    Aluminum foil muffin pans
    Stirrers

Key Questions

  • What is happening with the crystal solution? Why does it “grow”? What change of state is happening here? (Hint: Evaporation of water and ammonia).

What To Do

*Caution: Ammonia fumes are irritating, particularly to the eyes. Work in an area with good ventilation. Wear gloves and goggles.*

  1. To prepare the crystal growing solution, mix the following in a beaker or suitable container: 
  • 90 mL (6 tbsp) water
  • 90 mL (6 tbsp) liquid laundry bluing
  • 15 mL (1 tbsp) household ammonia
  • ​100 grams (6 level tbsp) table salt (NaCl)
  1. ​Stir until the salt is dissolved. Use immediately. Put the solution in an airtight bottle for short delays but do NOT store this solution because the solution decomposes to form cyanides.

Crystal Tree (grown on paper):

  1. Cut heavy blotter paper into the shape of a tree. Use the template that follows or create your own.
  2. To give the crystals some colour, put drops of food colouring on the tips of the branches and allow it to dry. 
  3. Place the tree in an aluminum foil muffin tin, and add 1 to 2 tablespoons of the crystal growing solution. Allow the tree to stand undisturbed for several hours or overnight. 

Crystal Garden (grown on rocky lump):

  1. Place a charcoal briquette or lava rock in an aluminum foil muffin pan. 
  2. To give the crystals some colour, put drops of food colouring on the briquette, rock or coal and allow it to dry before addition of the crystal growing solution. 
  3. Add 1 to 2 tbsp of the crystal growing solution around the briquette, lava rock, or coal. Allow the garden to stand undisturbed for several hours or overnight. 

Note: Depending on temperature and humidity conditions, crystals can begin growing within 2 hours. 

Teacher tip: Liquid materials used in this experiment can be washed down the drain with running water.

Extensions

  • Does adding more crystal growing solution lead to more crystals?

Other Resources

Science World Resources | Full Unit | States of Matter
Science World at TELUS World of Science | School Programs | Chemistry