Water and Hydrogen Bonding in Living Systems · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Why water clings, cools slowly and dissolves salt

Science · Organisms & Life Processes · ages 16-17
Name ______________________   Date ____________

  1. What causes cohesion and surface tension in water?

    • Water molecules sticking to surfaces like glue
    • Hydrogen bonds pulling between neighbours
    • Salt dissolved in the water

  2. What is a hydrogen bond in water?

    • One molecule's hydrogen end pulling on another's oxygen end
    • A strong shared-electron bond holding a single molecule together
    • A bond that only forms in ice

  3. Water warms up and cools down very quickly when heat is added or removed.

    Circle one:   True   False

  4. Why does adding heat raise the temperature of water only slowly?

    • Shaking the hydrogen bond network apart
    • Heat escapes through the surface at once
    • Water reflects most heat away

  5. You stir salt into one cup of water and oil into another. What happens?

    • Both vanish completely
    • Oil vanishes while salt beads up
    • Salt vanishes while oil beads up

  6. Why can an insect dent the surface of a pond without sinking?

    • The insect is lighter than air
    • Cohesion shares the load across the surface
    • Surface tension pushing up like a solid floor

  7. Water climbs thin plant stems because each molecule drags the next one along.

    Circle one:   True   False

  8. A student says droplets bead up because water is sticky like glue. What is wrong?

    • Droplets never bead up at all
    • Glue is stickier than any liquid
    • Neighbour bonds, not stickiness
LightMySky · lightmysky.comW1-mt_79dzlo6fD5-s1

Answer key

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

Why water clings, cools slowly and dissolves salt W1-mt_79dzlo6fD5-s1

  1. Hydrogen bonds pulling between neighbours · Neighbours holding hands explains beading and dented surfaces.
  2. One molecule's hydrogen end pulling on another's oxygen end · Opposite charged ends attract, linking neighbour to neighbour.
  3. False · Heat goes into shaking the bond network apart first, so temperature moves slowly.
  4. Shaking the hydrogen bond network apart · The network soaks up energy before the temperature can climb.
  5. Salt vanishes while oil beads up · Water grips the charged salt but finds no charged regions on oil.
  6. Cohesion shares the load across the surface · Linked neighbours spread the weight instead of letting go.
  7. True · Cohesion chains the pull from molecule to molecule up the stem.
  8. Neighbour bonds, not stickiness · Holding hands between neighbours pulls drops round, which glue style sticking cannot explain.
Worksheet · LightMySky