If you dissolve a whole sugar cube in water, does the water weigh more?
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If you dissolve a whole sugar cube in water, does the water weigh more?
The short answer
The sugar doesn't go anywhere — it's still in the glass, so the sweet water weighs more than the plain water did, heavier by exactly the weight of the sugar you added. Stirring breaks the cube into pieces too small to see, but it can't make them weigh nothing.
How it works
A sugar cube is just a huge crowd of tiny sugar pieces packed together. When you stir it into water, the pieces come apart and spread out evenly through the whole glass until they're far too small and scattered to see. They are still there, mixed among the water. A balance scale doesn't use eyes, only weight, so it still feels every piece. That's why a glass of plain water plus a sugar cube weighs the same before and after you stir, as long as nothing leaves the glass.
What people get wrong
Lots of people think that when something dissolves it is destroyed, so its weight disappears too. It isn't. Dissolving only hides the sugar by splitting it into specks too small to see and spreading them through the water. Nothing is created or destroyed, so the weight stays exactly the same.
The catch
Hidden is not the same as gone, but it isn't fully reversible by eye either. The sugar is 100% still there and you can taste it and weigh it, yet the pieces are now scattered all through the water, so you can't simply pick the cube back out. To truly get the sugar back you'd have to boil the water away and leave the sugar behind.
Questions kids ask
Does sugar water really weigh more than plain water?
Yes. If you add a sugar cube to a glass of water, the glass weighs more by the weight of that cube, both before and after it dissolves. The sugar is still in the glass; you just can't see it anymore.
If the sugar is still there, why can't I see it?
Stirring breaks the cube into pieces far too small for your eyes to notice, and spreads them evenly through the water. They're still floating in there, just too tiny and too spread out to see.
How can I get the sugar back out of the water?
You can't pick it out by hand because it's mixed through the whole glass. But if you let the water dry up or boil it away, the sugar is left behind, which proves it was there the whole time.
Is dissolving the same as melting?
No. Melting is when heat turns a solid into a liquid, like ice into water. Dissolving is when a solid's pieces spread out and mix into a liquid. The sugar isn't melting; its pieces are just splitting apart and hiding among the water.
For grown-ups
This is conservation of mass. Dissolving is a physical change: sucrose molecules separate from the crystal and disperse evenly among water molecules, held by hydrogen bonds, forming a homogeneous solution. No atoms are created or destroyed, so in a closed system the total mass is unchanged, and the dissolved sugar's mass is fully recoverable by evaporating the water. In an open glass a scale reading can drift slightly over time, but that is water evaporating, not the sugar vanishing.