The October 2017 PDX Parent features a recommendation for the new book Geology Lab for Kids by Garrett Romaine. Here’s a sample experiment from the book to try from home.
From Geology Lab for Kids by Garret Romaine
Grow your own perfect cube of salty perfection.
- 1 cup (235 ml) of water
- 7–8 tablespoons (126–144 g) of table salt (sodium chloride, NaCl). Iodized is okay.
- Food coloring (optional)
- Piece of cardboard (optional)
- Clean, clear container
- Saucer (optional)
- 12″ (30 cm) string or fishing line (optional)
- Scissors (optional)
- Pencil or butter knife (optional)
- Paper towel or coffee filter (optional)
-Don’t get salt in your eyes.
-Wash hands quickly after handling salt.
-Ask an adult for help boiling the water.
-Be cautious around the cooking stove to avoid burns.
STEP 1: First make a seed crystal by pouring a small amount of saturated salt solution onto a saucer or shallow bowl. As the liquid evaporates, crystals will start to form, usually overnight. Select a single square crystal and remove it from the dish.
STEP 2: Carefully pour the saturated salt solution into a clean container (making sure no undissolved salt gets in), allow the solution to cool, and then hang the seed crystal with string in the solution from a pencil or knife placed across the top of the container. You could cover the container with a coffee filter or paper towel to keep out dust yet permit evaporation.
STEP 3: Set the container in a location where it can remain undisturbed. You are more likely to get a perfect crystal instead of a mass of crystals if you allow the crystal to grow slowly (cooler temperature, shaded location) in a place free of vibrations. It can take a week or more to get a big crystal.
- Experiment with different types of table salt and water. See if there is any difference in the appearance of the crystals.
- If you are trying for the “perfect crystal” use un-iodized salt and distilled water. Impurities in either the salt or water can aid in dislocation, in which new crystals don’t stack perfectly on top of previous crystals.
- Make a mass of crystals by pouring the saturated salt solution into a clear container. Let it slowly evaporate. Crystals will grow on the sides of the container.
THE SCIENCE BEHIND THE FUN
The hardest part of this experiment is tying the thread around your seed crystal. But without the seed crystal, it’s hard to get much more than crusty salt. The perfect seed crystal gives the extra salt in your solution perfect little places to attach to, and this is what will keep the crystal structure growing. This is the crystal lattice we discussed earlier. Salt has a perfectly cubic crystal lattice. It measures the same distance on all sides, no matter how big or small.
Salt is pretty simple. It has one sodium atom (Na) and one chlorine atom (Cl), clustered together over and over, to form a salt molecule. Thus the formula for salt is easy: NaCl. In the crystal lattice, the atoms repeat in every direction. Where there is a Cl atom showing, an Na atom can attach, and vice versa.
Salt is mined in many ways. In some places, solar evaporation of salt water produces salt crystals. There are also underground mines in salt domes where miners scoop up salt crystals or cut slabs of hardened salt into blocks. Some specialty shops sell salt from all over the world, which shows that salt is still an important part of our diet.