It's fun and easy to make your own snowglobe using water and 'snow' made from glitter or crushed egg shells, but you can use chemistry to make crystal snow that looks a lot more like the real thing. Snow is made from crystals of water. In this project, you precipitate crystals of benzoic acid, which has the advantage of not-melting at room temperature. Here's how you make the snow globe:
- baby food jar or ointment jar (~4 oz)
- 1 g benzoic acid
- beaker or pyrex measuring cup
- hot plate or microwave or coffee maker
- stirring rod or spoon
- hot glue gun
- decoration to glue to the bottom of the snow globe, like a small plastic toy
- forceps or tweezers
- electrical tape (optional)
- There are a couple of ways to do this. There is my do-it-at-home method and then what you might want to do in a lab. Let's start with the lab instructions...
- In a 250 ml flask, stir 1 g benzoic acid into 75 ml of water.
- Heat the solution to dissolve the benzoic acid. You do not need to boil the water.
- Alternatively, you can measure 75 ml (5 tablespoons) of water that you heated in a microwave or coffee maker. Dissolve the benzoic acid in the hot water.
- Put down a bead of hot glue on the inside of the jar lid (or you can put it on the bottom of a clean, dry jar if you don't plan to invert the sealed jar).
- Use tweezers or forceps to position your decoration in the glue.
- While the glue is cooling, take a look at your benzoic acid solution. As it approaches room temperature, the benzoic acid will precipitate out of solution to form "snow". The rate of cooling affects the 'snow'. Slow cooling produces fine crystals. Quick cooling produces something more like snowballs than snowflakes.
- Pour the room-temperature benzoic acid solution into the glass jar.
- Fill the jar as full as possible with water. Air pockets will cause the benzoic acid to form clumps.
- Put the lid on the jar. If desired, seal the jar with hot glue or electrical tape.
- Gently shake the jar to see the pretty snow!
Benzoic acid doesn't readily dissolve in room temperature water, but if you heat the water the solubility of the molecule is increased (similar to dissolving sugar in water to make rock candy). Cooling the solution causes the benzoic acid to precipitate back into solid form. Slow cooling of the solution allows the benzoic acid to form prettier, more snow-like flakes than if you had simply mixed benzoic acid powder with water. The cooling rate of water into ice affects how real snow appears, too.
Benzoic acid is used as a preservative in food, so as chemicals go it is pretty safe. However, pure benzoic acid can be very irritating to skin and mucous membranes (here's an MSDS for you). Also, it can be toxic if large quantities are ingested. So... wear gloves and eye protection when preparing your solution. Excess solution can be washed down the drain (can neutralize it with baking soda first if you like). I wouldn't recommend this project for very young children. It should be fine for grade school kids with adult supervision. It's mainly intended as a fun project for teens and adults. The snow globe is not a toy -- you don't want young children taking it apart and drinking the solution.