Grow a crystal garden and explain what has happened
Cardboard (not corrugated), scissors, food colouring, bowl, measuring spoons, water, non-iodised salt, liquid bluing, ammonia
Bluing is hard to find in NZ - you can make a suspension of Prussian Blue pigment instead (1:1 ratio with water). Prussian blue pigment can be found at art supply stores. You can do the experiment without the bluing/Prussian blue solution but it won't work as well.
Mini Crystal Garden
Epsom salt, glass jar, food colouring, warm water, measuring cups, spoon or mixing stick, fridge
Grow crystals on charcoal
Charcoal (or a sponge instead), non-iodised salt, liquid bluing, ammonia, water, food colouring, glass dish, bowl for mixing, measuring spoons
Trace tree shape onto cardboard and cut out.
Cut a slot down the middle of both tree shapes, one starting from the top to the middle and one starting from the bottom to the middle.
Slot the two shapes together to form a 3D tree that will stand on its own.
Add drops of food colouring to the edges of the tree and allow to soak into the cardboard.
In a bowl mix together 1 tablespoon water, 1 tablespoon salt, 1 tablespoon bluing, 1/2 tablespoon ammonia
Stand your tree in the middle of the solution. Watch what happens for the next 10-12 hours.
You could make at your meeting and send the tree and the solution in a spill-proof container home with the girl with instructions on what to do at home. Ask them to take a photo of their tree.
Mini crystal garden
In a glass jar combine Epsom salt and warm water using a 1:1 ratio.
Stir the salt and water until most of the salt is dissolved.
Add a few drops of food colouring if you want colourful crystals.
Place the jar in the fridge for at least a day (but longer is ok).
Remove from fridge and carefully pour out excess water.
You could experiment with different ratios of salt and water, or the temperature of the water or try initial freezing or...
Probably best to take this one home with a leader and bring back to finish the next week. They can't be out of the fridge for long before pouring off the liquid.
Grow crystals on charcoal (or a sponge)
Put some charcoal (or a sponge) in the bottom of a glass dish.
Spray the charcoal (or sponge) well with water.
Mix together 3 tablespoons salt, 3 tablespoons ammonia and 6 tablespoons bluing. (you may want to do this outside - it smells strong).
Pour mixture evenly over the charcoal (or sponge).
Sprinkle with 2 tablespoons of salt.
Add drops of food colouring to get a colourful crystal garden.
Wait. To keep the garden growing, every two days mix 2 tablespoons salt, 2 tablespoons bluing and 2 tablespoons ammonia and pour around the base of the charcoal (or sponge).
Send home with girl/give each girl a glass jar and send home with them. Get them to take photos
The main principles at work here are capillary action, evaporation, crystaliztion, and saturation.
Capillary action is the same process that enables plants and trees to take water and nutrients from the soil up through their stems or trunks and into their leaves, branches, flowers, and fruit. The cardboard tree uses the same process to draw the magic solution up through its entire shape until the cardboard has soaked itself in the solution.
After the magic solution has been drawn throughout the tree by capillary action, the solution begins to evaporate. The evaporation process is accelerated by the ammonia, which evaporates more quickly than water. As the magic solution evaporates off of the tree, the crystals are left behind on the branches of the tree.
The magic crystals that are left behind are a combination of the Bluing and the table salt. The solution that you created is supersaturated by the bluing and salt that you add to the water. The bluing is a colloid, with many tiny particles suspending themselves within the water. It’s just like when you shake up a snow globe, except the particles of bluing are much smaller than the snow. As the bluing and salt water make their way up the tree, the water begins evaporating. These means there is less water able to support the bluing particles and dissolved salt. This evaporation allows the salt and bluing particles to crystallize, resulting in your beautiful tree.