Growing Salt Crystals by Evaporation

An adult should keep the salt and the drying dish out of reach of younger children. Do not eat or drink the salt, the salty water or the crystals. No heating is needed: use water at room temperature.

Protective equipment and “do not substitute” warnings have not been recorded for this experiment yet. They are added when its safety review is completed; until then, follow the supervision notes above.

Disposal: Dissolve the crystals in water and pour them down the sink with running water, or put them in general waste.

Do not start this experiment until an adult who has read the supervision notes above is present.

An adult needs to be here first

The materials (5) and steps (5) for this experiment are hidden until an adult who has read the safety information above is present.

What you should see

• Over a few days the liquid disappears and white crystals appear, starting at the edges.
• Under the magnifying glass many crystals are little cubes, or are built from square, stepped shapes.

Why it works

When no more salt will dissolve, the solution is saturated: it holds as much salt as it can at that temperature. As water evaporates from the saucer there is less water to hold the salt, so salt comes out of the solution as solid crystals.

Salt is sodium chloride. In the solid, sodium and chloride ions are packed in a regular cubic pattern, and that repeating cubic arrangement is why salt crystals grow as cubes.

Learn the ideas behind it

• Chemical Bonds
• States of Matter

Sources

• Chemistry 2e, 11.3 Solubility — OpenStax
• Chemistry 2e, 10.6 Lattice Structures in Crystalline Solids — OpenStax