[mooeypoo]

Me again with my kitchen experiments.

So, I'm going to show (again) how pouring salt on an ice cube makes it melt FASTER. I will have a control ice cube with nothing on it and another cube with something like sugar (to show it's not just the "powder").

I am trying to look for a substance that can do the opposite and actually increase the freezing point of water, hence keeping the ice from melting *longer*.

Anyone knows of any such substance? What, in this case, is the opposite of salt? I'm trying to look it up online but so far with little success. I'll post it here if I find anything.

IF there is such a substance (and .. there must be!) I sure hope it can be found in a kitchen

~mooey


EDIT: Waa.. seems it's not possible: http://www.newton.de...3/chem03446.htm
I rely on your imaginative ideas, then, if it is at all possible....

[Cap'n Refsmmat]

Indeed; freezing point depression does not depend at all on the substance dissolved in the water, but only its quantity, so there's no solute you could add that would elevate the freezing point without changing the chemical properties of water.

http://en.wikipedia....gative_property

Now, you could perhaps mix the water with other liquids, but that's a different mechanism entirely.

[Moontanman]

Hmmm, an anti anti freeze, that is a challenge.

Maybe you should try this experiment, I'm not sure how you would lay it out but you can use salt to freeze water....

Oh and another thing, aspartame, or at lest diet soda seems to freeze faster than regular soda, that could be a starting point to investigate.

This post has been edited by Moontanman: 8 June 2011 - 03:51 PM

[mooeypoo]

Moontanman, on 8 June 2011 - 03:50 PM, said:

Hmmm, an anti anti freeze, that is a challenge.

Maybe you should try this experiment, I'm not sure how you would lay it out but you can use salt to freeze water....

Oh and another thing, aspartame, or at lest diet soda seems to freeze faster than regular soda, that could be a starting point to investigate.

Salt would melt the ice, and would decrease the freezing point of water.... so that won't work.



What I ended up doing is just comparing between the ice cube (with nothing), ice cube(with sugar) and ice cube(with salt). Sugar and salt were much faster than the "empty" cube, but clearly salt is MUCH more efficient in making the ice melt.

That could be a good demo. I just wanted to see if there's a way to make it even better.

[Hal.]

Mooeypoo , Can water be made to freeze at a higher temperature than usual by manipulating the pressure ?

[Cap'n Refsmmat]

mooeypoo, on 8 June 2011 - 03:56 PM, said:

What I ended up doing is just comparing between the ice cube (with nothing), ice cube(with sugar) and ice cube(with salt). Sugar and salt were much faster than the "empty" cube, but clearly salt is MUCH more efficient in making the ice melt.

If you used exactly two times as many moles of sugar as of salt, they'd be equally effective. The effectiveness of salt is because it dissociates in solution into two particles, Na+ and Cl-, while sugar does not. The nature of the solute is otherwise unimportant, interestingly enough.

[imatfaal]

I dunno if this is what Moontanman meant - but you can use a ice, salt and one container within another to make ice cream. It definitely works (although I have not tried the two tin method linked) - the salt water is able to be cooled to a lower temperature by the ice cubes, which means that it can draw the heat from the cream till the cream freezes.

Now tell me an experiment that ends up with making ice cream isn't a winner with kids

[mooeypoo]

imatfaal, on 8 June 2011 - 04:41 PM, said:

I dunno if this is what Moontanman meant - but you can use a ice, salt and one container within another to make ice cream. It definitely works (although I have not tried the two tin method linked) - the salt water is able to be cooled to a lower temperature by the ice cubes, which means that it can draw the heat from the cream till the cream freezes.

Now tell me an experiment that ends up with making ice cream isn't a winner with kids

Indeed, I know. Thing is -- kids aren't really too surprised that ice makes something freeze. While it RESULTS in a cool ice cream, it's not much of a science demo; the kids aren't SURPRISED that the cream cooled to be ice-cream.

The salt-on-ice demo is a bit better since they can see very well that the ice melts MUCH faster with ice on it, and slightly faster with sugar on it, and slower without anything on it.

Hal., on 8 June 2011 - 04:07 PM, said:

Mooeypoo , Can water be made to freeze at a higher temperature than usual by manipulating the pressure ?

Yes, but you need quite a large pressure (which is extremely hard to do in a kitchen) and even that will only result in a VERY small change. Probably too small to observe without some computer probes.

[John Cuthber]

On a mole for mole basis salt is roughly twice as effective as sugar at lowering the freezing point (for the reason given above)
The problem is that anything that dissolves will have the same effect.
If you want a "control" experiment with a powder try sand.

At any reasonably sensible pressure the effect of pressure on freezing point is to raise it.
Once you get above about 2000 atmospheres the pressure starts to rise with pressure.
Don't try this at home.

[Hal.]

So , if let's say we wanted to freeze water at 100 degrees celsius , what pressure would be needed ?

[mooeypoo]

John Cuthber, on 8 June 2011 - 06:03 PM, said:

On a mole for mole basis salt is roughly twice as effective as sugar at lowering the freezing point (for the reason given above)
The problem is that anything that dissolves will have the same effect.
If you want a "control" experiment with a powder try sand.

At any reasonably sensible pressure the effect of pressure on freezing point is to raise it.
Once you get above about 2000 atmospheres the pressure starts to rise with pressure.
Don't try this at home.

I don't think I *can* try this at home, unless I talk to the ice really fast and obnoxiously... har.

Anyhoo, I think what I'll do is a bit of a reframing of the experiment. Instead of comparing "powers" I will show the difference of regular melting vs. melting with a solvent -- so sugar vs salt. The salt made it melt much faster, and the sugar made it melt a tad slower. That's enough to also explain why we use Salt on the pavements and not something else.

Also, sugar will make the pavement sticky....

[Cap'n Refsmmat]

mooeypoo, on 8 June 2011 - 06:16 PM, said:

Anyhoo, I think what I'll do is a bit of a reframing of the experiment. Instead of comparing "powers" I will show the difference of regular melting vs. melting with a solvent -- so sugar vs salt. The salt made it melt much faster, and the sugar made it melt a tad slower. That's enough to also explain why we use Salt on the pavements and not something else.

Sugar is a solute as well, so I'm not sure what you're getting at here. Did the sugar make it melt more slowly overall, or just more slowly than the salt did?

mooeypoo, on 8 June 2011 - 06:16 PM, said:

Also, sugar will make the pavement sticky....

That's good for traction, right?

[mooeypoo]

Cap, on 8 June 2011 - 06:51 PM, said:

Sugar is a solute as well, so I'm not sure what you're getting at here. Did the sugar make it melt more slowly overall, or just more slowly than the salt did?


That's good for traction, right?

Meh, I'm having a brainfart day.
Let me see that I get it. Both are *solutes* (as in, they both dissolve in water).



The sugar make the ice melt faster than regular ice, but not as fast as the salt. Which makes sense according to the posters here.