7 replies to this topic

[RandomQuestion]

I'm not a Chem-E, but this is a chem-E question I think.... My husband recently had a highly saturated sugar soln that boiled over and melted our new (sniff) glass stove-top... "How could this have happened??" he asked, the liquid can't be hotter than the stove, the stove is what is heating it - so if it is not hotter than the stove, then how can it melt the stovetop???  I think the answer has something to do with latent heat?  exothermic solidification?  I'm curious to hear what a Chem-E would say about it though. 

[DhuriS]

Hello,

 

The thing happened with you is pretty obvious.

 

First thing; the solution of sugar + water is called syrup.

 

Second thing; a saturated solution means that the solution contains solute to such extent that is can't just accommodate further addition of solute.

 

Heating the saturated solution for long time  (that I think your husband did) starts a process called CRYSTALLIZATION; wherein crystals start to form in and over small cracks (called nucleation sites) of container.(this process is used generally in sugar industry)

 

 

Now the key point is :: the process of crystallization gives off heat ;that means it is an  "Exothermic" process.

If the temperature of system increases to the extent over the melting point of material/metal used (here stove); might meld it down.

Now in this case you have not mentioned the exact material of your glass stove; which I think is a key factor in this case.

[DhuriS]

one more point;

 

overall effect of heating saturated sugar syrup in your case caused the temp. of system to rise because exothermic heat given out of process + heat supplied to stove together increased the whole temp. of system to such high degree that finally melted your stove.

 

you have quoted a sentence ""the liquid can't be hotter than the stove, the stove is what is heating it"" ;-- this is not true as here "liquid" (we call it soln) is giving off exo. heat and at the same time you are providing (extra) heat through stove.

[RandomQuestion]

Thanks for the reply!  but I thought temp remains constant during phase changes?

[PingPong]

I don't have a glass top stove, but I can not believe that some over boiling syrup can melt glass.

Melting temperature of glass is extremely high.

 

Are you sure the glass did really melt? Or could it be that what you think is melted glass is merely a crust of burned sugar?

Did you make pictures of the "melted" stove top?

[RandomQuestion]

Sorry for the late reply, it really did melt it!  Just posted a pict - it was jello.

Edited by RandomQuestion, 08 November 2014 - 08:36 PM.

[PingPong]

So the syrup burned pits in the glass.

 

I cannot imagine that the the syrup temperature in the pan could have been higher than the melting temperature of glass.

However if the syrup contains certain salts that can form a eutectic system with the glass, the melting point of that eutectic could be lower than the syrup temperature, and consequently the eutectic parts melt.

[JMW]

It is an interesting question to which I can add nothing as to what happened or why.

 

However, it now depends on where you are.

 

This is a new stove and you are unhappy with the pits in the glass?

I don't think it unusual that anyone would heat a sugar solution nor boil it over.

It happens all the time that saucepans boil over and sugar solutions can be a normally expected event.

 

It becomes a question of "fit for purpose".

The manufacturer should be approached and asked how it can be that the glass can become pitted by boiled over sugar solution if the glass top is supposedly designed for domestic cooking purposes.

 

I note in the photos that in cleaning the glass there are signs of vigorous scrubbing with some sort of scotch pad. This doesn't suggest to me a normal glass top. The pattern does not suggest your husband (I assume he was told that since he did it he should clean it up) resorted to any power tools for the clean up.

 

The manufacturer may, if approached in the right way, replace the top under warranty but they may also try to wriggle out out any obligation by relying on suggesting that what you did was not a normally anticipated occurence, not something they should consider in their design. 

 

But boiling over saucepans is a common occurence and boiling sugar solutions is too.

 

But was this a normal sugar solution? You say "a highly saturated sugar solution" rather than simply "highly saturated sugar solution".

Was your husband doing something other than using normal sugar? Sugar as a chemical term is not necessarily the stuff we put in our tea or coffee....  or something like "sugar of lead"? was he perhaps not being completely open about what he was doing boiling up a sugar solution?

 

.... but then there is this thread here: http://libanswers.cm....php?qid=166004In it note that the questioner there says there was some sort of warning in the handbook.....(?).