Stir sugar into water and the crystals seem to disappear.
They are not gone.
The sugar molecules have simply spread through the liquid.
A sugar crystal contains many molecules
The visible crystal is a large organized collection of sugar molecules.
Water molecules are attracted to parts of those sugar molecules.
When water reaches the surface of the crystal, it can begin pulling individual sugar molecules away.
The molecules spread through the water
Once separated from the crystal, sugar molecules become surrounded by water molecules.
They move throughout the liquid.
You can no longer see the original crystal because the sugar is no longer concentrated in one visible solid piece.
How do you know the sugar is still there?
Taste the water.
The sweetness remains.
Or allow the water to evaporate.
As water leaves, sugar can eventually form crystals again.
Dissolving changed the arrangement.
It did not destroy the sugar.
Why does stirring help?
Stirring constantly brings fresh water into contact with the crystal surface.
It also carries dissolved sugar away from that immediate area.
That helps the dissolving process continue efficiently.
Why does warm water usually dissolve sugar faster?
Warmer molecules move more quickly.
That increases the rate at which water interacts with the crystal.
Warm water can also hold more dissolved sugar under ordinary conditions.
How is this different from oil and water?
Sugar interacts favorably with water, so individual sugar molecules can become surrounded and dispersed.
Oil behaves differently, which is why oil separates and floats on water instead.
One substance dissolves.
The other forms a separate layer.
So the sugar did not actually disappear.
It stopped traveling as one visible crystal and spread out molecule by molecule.
And that’s the short explanation.
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