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What causes boiling water to boil more violently when I pour granulated sugar into it?

1305277631 67 What causes boiling water to boil more violently when I pour granulated sugar into it?

I brought water in a cup to a boil in a microwave, then pour granulated sugar in to it. (It's to make a solution for hummingbird feeders.) the water, lightly boiling when removed from the microwave, violently churns when I slowly pour granulated white sugar into it.

Am I right in assuming this effect is due to the water being superheated, and the sudden disruption of the sugar being added causes the bulk of the water to boil? Is it air being purged out between the small crystals of the sugar, since the vapor pressure of the water is above the partial pressure of the air? Or something else? Or a combination of effects?

Some things raise the boiling point and some things lower it.
When you put the sugar in it obviously lowers the boiling point.
The water then boils vigorously because it is now above the boiling point and must release the extra heat.

Also some things (probably not sure) actually releases heat when mixed with water. one example is concentrated acid.

Yes. it was super heated. this is a major danger of heating pure water in a microwave. There's very little convection or anything else to disrupt the water, also the temperature is more uniform whereas in a pot the surface of the pot on the burner is much hotter then the water and therefore the water directly against it is hotter. Therefore it heats up to much higher then the boiling point. this is a very unstable state however and any slight jar or irritation, like sugar, causes it to burst out of liquid form into steam quite violently.

Sugar poured into 100C water would have the effect of stopping the boil because it raises the boiling point.

I don't know about sugar but salt raises the boiling point of the water so it seems to boil harder. Maybe it's the same for sugar…

raising the molecular weight of the solution raises the boiling point. salt is Na and Cl both heavier than H and O. Sugar is primarily H and C, and C is lighter than O so the molecular weight of the mixture goes down, lowering the boiling point.

no, but i stayed at a holiday inn express last night

I believe that dissolving sugar in water lowers the boiling point of the water. It's been a long time since freshman chemistry…

Water and sugar boil at a "Higher" temperature.
There is a heat from solution. the sugar dissolving adds heat to the water. if the water is at boiling temperature the extra heat is added to the latent heat changing water to gas.
Try this carefully in a sink, with glasses. to hot, not boiling, water and add lye. this can boil over. this is definitely not from superheated. this is why one adds acid to water and not the other way around.

Although superheating is possible, and may be contributing, I don't think it is the primary effect.

The boiling point of water is affected by dissolved materials in the water. Sugar water will actually boil at a lower temperature than pure or purer water. When the sugar is added, the mixture is now above its boiling point (kind of like superheating but with a different mechanism).

The effect is also seen with freezing point, which is why we put salt in our ice cream freezer ice, to make a material that is melting at a colder temperature than water, which can then freeze icecream which freezes below 32F (because of the sugars etc)

I don't know. but it stops boiling when I put salt in it.

I did an experiment on that in 6th grade. the sugar is easily dissolved by the super-heated water, and it causes the water to boil… could be a combination of effects… I agree with the dude: the sugar could decrease the boiling point of water, which would make sense, since the water is already boiling.

Salt, sugar, and practically any other substance elevates the boiling point and therefore shortens cooking time.

Some dumb answers here.

For a start, adding sugar raises the boiling point.
And sugar has positive heat of solution, so adding it lowers the temperature.

Which leaves your original hypothesis. Sugar crystal give nucleation points for boiling in the superheated water. the same thing does not happen with water from a freshly boiled kettle.

What causes boiling water to boil more violently when I pour granulated sugar into it?

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