Melting, dissolving, mixing: name the change

Discover

Melting changes a solid into a liquid. When ice melts, the resulting liquid is still water. Energy arriving from warmer surroundings allows the organized solid structure to change. No second ingredient is needed to make the water into a liquid. A smaller piece of ice and a puddle are visible clues, although appearance alone does not explain the molecular process.

Dissolving involves one substance spreading among the particles of another. Stir sugar into water and sucrose molecules leave the crystal and mix among water molecules. They have not become liquid sugar. The sugar remains present even when individual grains are too small to see. Table salt also dissolves, but its crystal separates into sodium and chloride ions rather than intact salt molecules.

Mixing is a broader description of bringing materials together. Some mixtures become solutions, while others keep separate pieces, droplets or layers. Shaking oil and water distributes one liquid as droplets in the other for a time; it does not make the oil dissolve. A cloudy appearance can mean that light encounters many droplets, not that a new solid has appeared.

Bring it into the kitchen.

A recipe may use all these changes. Ice melts in a drink; sugar dissolves in its water; a dressing mixes oil with a water-based ingredient. Choosing the right word helps explain the action you need. More shaking can make smaller droplets, but it cannot turn an oil-and-water mixture into a sugar-water solution.

Try it

One small observation.

• Open Where did the crystals go? Predict what will remain visible, then follow the equal-mass comparison and its matched water, temperature and swirling conditions. Observe the bottoms as well as the sides of the cups.
• Write two statements separately: what you saw, and what the explanation suggests. For example, “I see fewer grains” is an observation; “some sugar dissolved” is an interpretation supported by the setup. Do not taste investigation samples to test the idea.