Why Some Things Dissolve and Others Do Not · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Why salt dives in and oil stays out

Science · Matter & Materials · ages 15-16
Name ______________________   Date ____________

  1. Sugar dissolves in water, so sugar water carries an electric current well.

    Circle one:   True   False

  2. You stir salt into water and the grains disappear. What happened?

    • It vanished into nothing
    • It traded crystal pulls for water pulls
    • It turned into water molecules

  3. Why does oil refuse to dissolve in water?

    • Water is polar and cannot grip nonpolar oil
    • Oil is heavier than water
    • Water splits oil into ions

  4. In the hot ice trick, why does touching the liquid start crystallising?

    • The touch cools the liquid fast
    • The crystal heats the liquid up
    • The cold liquid held extra salt, and the crystal starts the crash

  5. A nonpolar solid dissolves best in which liquid?

    • A nonpolar solvent
    • Pure water
    • Salt water

  6. A curve reads 70 grams at 80 degrees and 40 grams at 30 degrees. A 70 gram load cools from 80 to 30. How many grams crystallise?

    Answer: ______________

  7. Two unlabeled beakers hold salt water and sugar water. How do you tell them apart safely?

    • Weigh them, since sugar water is always heavier
    • Test which one carries a small current
    • Salt water always looks cloudy

  8. A student stirs sugar into oil, sees grains sitting, and says sugar never dissolves in anything. What is the mistake?

    • Sugar needs a matching polar solvent like water, not oil
    • The oil was not hot enough
    • Sugar only dissolves in oil
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Why salt dives in and oil stays out W1-mt__njIrlqqqL-s1

  1. False · Sugar stays whole and uncharged, so it cannot carry current.
  2. It traded crystal pulls for water pulls · Water pulled the ions apart and surrounded each one.
  3. Water is polar and cannot grip nonpolar oil · The pulls mismatch, so no trade happens.
  4. The cold liquid held extra salt, and the crystal starts the crash · Supersaturated water holds extra salt until something triggers it.
  5. A nonpolar solvent · Matching pulls mix, so nonpolar meets nonpolar.
  6. 30 · Subtract the cold limit from the hot load: 70 minus 40 is 30.
  7. Test which one carries a small current · Only the free ions in salt water can carry current.
  8. Sugar needs a matching polar solvent like water, not oil · One failure in oil says nothing after water was never tried.
Worksheet · LightMySky