Dissolving salt or sugar doesn't change it
- The idea
- Predict
- See it
- Why
- Check
The idea
“When something dissolves, the water reacts with it and turns it into a new substance.”
The crystal vanishes, so it looks destroyed. It's still there, split into tiny particles with water around each one.
The short version
The mistake: When something dissolves, the water reacts with it and turns it into a new substance.
What's actually true: When salt or sugar dissolves, water surrounds each ion or molecule, and no new substance forms.
- Water is polar. Its oxygen end has a partial negative charge, and its hydrogen ends have partial positive charges.
- Those charges attract ions and polar molecules. Water surrounds each particle in a hydration shell and pulls it away from the rest.
- For salts and sugars, no covalent bonds form or break. Water clings to ions by their charge and to sugars by hydrogen bonds.
- Oils are nonpolar, so water has no charges to attract. Its molecules stay hydrogen bonded to each other, and oils don't dissolve.
On the exam: Dissolved salt or sugar is only surrounded by water. Dry it out and you get the solute back.