Can you keep stirring sugar into water forever?
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Make Your Own Rock Candy! | The Science of Cooking! | SciShow Kids
Follow hot water as it dissolves extra sugar, then watch that sugar reappear as crystals on a chopstick—with a grown-up handling the stove.
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What else makes you wonder?
Would the same cup hold equal amounts of salt and sugar?
Keep the water amount and temperature fixed, then compare two different solids.
Where does the water level move when sugar disappears from sight?
Watch the liquid line closely before and after adding a measured amount.
Would tiny sugar grains disappear faster than one big lump?
Think about how much sugar surface can touch water at once.
After you watchCan you keep stirring sugar into water forever?
The short answer
Yes. At a given temperature, water can reach a dissolving limit for sugar. At that saturated point, adding more sugar leaves extra solid behind even though individual sugar particles still move between the liquid and the solid.
Try this next
- What if you used warm water for the first spoon? Predict whether the full point moves, then compare equal water amounts at two temperatures with adult help.
- What if you stopped stirring and waited? Predict whether the same amount can dissolve more slowly, then compare matched samples without changing their temperature.
- What if the glass held twice as much water? Keep the temperature and spoon size the same, then predict how the amount of water changes the total sugar that can dissolve.
The whole story
How it works
Dissolving is a two-way particle process. Sugar particles leave the solid and spread through the water, while other dissolved sugar particles can rejoin the solid. Before saturation, more leave than return. At saturation, the average rates balance, so the dissolved amount stays steady while extra solid may remain.
What people get wrong
Stirring faster does not create extra dissolving capacity at the same temperature. It moves fresh liquid past the solid and helps the mixture approach its balance point sooner, but a gently stirred and a vigorously stirred sample can reach the same final dissolved amount.
The catch
Temperature can move sugar's dissolving limit: warmer water generally dissolves more sucrose than cooler water. Stirring mainly changes how quickly the system approaches its limit; changing temperature can change the limit itself.
Questions kids ask
Why can extra sugar remain at the bottom?
At that temperature, the solution has reached its sugar limit. Sugar still moves both ways between liquid and solid, but the average amount dissolved no longer increases, so added solid can remain.
Does stirring harder dissolve more sugar?
At the same temperature, stirring usually changes the speed, not the final limit. It brings liquid past the sugar faster, helping the system reach the same balance sooner.
Does warm water dissolve more sugar than cool water?
For sucrose, yes. A warmer sample can have a higher dissolving limit than a cooler sample, although different substances can respond to temperature in different ways.
What does saturated mean?
A saturated solution is at its dissolving limit for a substance under those conditions. Dissolving and return to the solid can still happen, but their average rates balance.
Talk about it
- Before each spoon, ask: will all of this one spread through the water, or will some solid remain?
- What evidence shows that stirring changes the speed but not the fixed-temperature limit?
- How can sugar still be present when the drink looks clear?
For grown-ups
This story models a saturated sucrose solution as dynamic equilibrium rather than a set of occupied molecular seats. Dissolution and return to the solid continue in both directions, while their average rates become equal at saturation. Agitation changes transport and rate, not equilibrium solubility at fixed temperature. Sucrose solubility in water is temperature-dependent, and the final gated experiment asks children to apply that relationship to a new setup.