Evaporation
Evaporation is when a liquid turns into a gas and moves into the air, even without boiling.
A pot of water sits on the stove with the lid off. The water molecules near the top have enough energy to break free and float up into the air as invisible vapor. You do not see them leave, but the water level slowly drops. The same thing happens to a puddle on the sidewalk on a sunny day — no boiling needed.
Explaining evaporation by grade level
When you mix salt, bluing, and ammonia in a dish, the wet liquid slowly disappears into the air. That is evaporation. As the liquid goes away, the salt and bluing have nowhere to go, so they stack up into tiny, beautiful crystals. The water left, but the solid parts stayed behind.
Projects that explore evaporation
Liquid water turns into gas and moves into the air — that process is evaporation. Three factors control how fast it happens: temperature, wind, and surface area. When you aim a fan at a wet sponge, the moving air carries water vapor away faster than still air does. Hot water leaves a sponge faster than cold water, and a larger sponge exposes more surface for water to escape from.
Most of an orange is water — far more than you might expect. When you dry the slices under a desk lamp and fan, that water turns into gas and moves into the air. The dried orange weighs a fraction of the original. In this experiment, the orange lost about 81 percent of its weight as water escaped into the air.
When the liquid in the mixture turns to gas and moves into the air, the salt dissolved in it has nowhere to go. It joins together in a repeating pattern and forms feathery crystals across the sponges. The ammonia speeds this process so the crystals form faster. The bluing supplies tiny particles for the crystals to grow on, and the table salt provides the building material.
When a mixture evaporates, the liquid turns to gas and moves into the air. Anything dissolved in that liquid stays behind as a solid. You prepare four bowls — each holds a different combination of salt, water, bluing liquid, and ammonia — and place a sponge in each one. As the water evaporates over ten days, the salt left behind forms crystals whose size depends on what was in the bowl.
During a dissolving experiment, some liquid can turn to gas and move into the air. In this experiment, you measure the temperature of the water, add different substances, and measure how much dissolves. Any water lost to evaporation means less liquid is left to dissolve the substance.