Depth 1 · 45 s
Where the sugar goes
Stir sugar into water and it disappears, yet the water tastes sweet and the scale reads the same. Up close, water particles pull the sugar apart, one particle at a time.
About this video
Stir a spoonful of sugar into a glass of water. For a moment you can see the white grains swirling. Then they are gone and the water looks as clear as before. But it tastes sweet, so the sugar hasn't vanished.
There is a second way to check. Put the glass of water and the sugar on a kitchen scale together and write down the number. Stir the sugar in until it is gone and weigh again: the scale shows the same number. The sugar is still in the glass. When something mixes into a liquid like this and seems to disappear, we say it dissolves, and the clear mixture you get is called a solution.
The particle model explains it. A grain of sugar is a huge crowd of sugar particles stuck together. The moving water particles bump into it and pull sugar particles away, one by one, and they spread out between the water particles all through the glass. Each one is far too small to see, which is why the water looks clear and tastes sweet everywhere, at the top and at the bottom. Warm water dissolves sugar faster, because its particles move faster, and stirring helps too.
Not everything dissolves. Salt and sugar are soluble in water. Sand is insoluble: it swirls about and then sinks, still sand. Cooking oil doesn't dissolve either; it floats on top in a layer.
This video shows depth 1 of Dissolving.
Learn DissolvingTranscript
- 0:00Stir a sugar cube into water. Soon you can't see it. But the water tastes sweet.
- 0:08Weigh the glass and sugar before stirring, and after. The scale shows the same number.
- 0:15Up close, moving water particles bump into the sugar and pull its particles away, one by one, until they are spread through the whole glass.
- 0:28Salt dissolves in water too. Sand sinks, still sand. Oil floats on top.
- 0:38The sugar didn't vanish. It spread out.