Friday quiz

[AstralTraveller]

I saw a rather neat photo the other day and I thought I'd share it. And set the explanation as a little quiz!

The photo shows a beaker of water with two ice cubes in it. One is floating at the surface, just as expected. The other, however, has sunk to the bottom. It isn't an optical illusion. There isn't a lead sinker in the second cube. Nor is there any other trickery. The explanation relies on science. What is going on?

BTW There are a few of you out there who will solve this in a millisecond, .... or bloody well should!! :P How about letting those who have to get the thinking caps on have their bit of fun?

[julianh72]

Spoiler alert:
The sinking cube is made of salty or sugary water?

[GeoffW1]

Aha,

But OK, I'm not saying

:D

[Baddad]

Interesting,
Heavy ice? LOL

[AstralTraveller]

Hmmmm.

[FlashDrive]

How about ... 1 block of ice is made from ' distilled ' water ( like rain water )...is the one that floats...

and ... the one on the bottom is made of ordinary tap water ... so it would have ' heavy metals ' in it...causing it to drop to the bottom.

That's my educated guess ..... do I go to the top of the Class ... :D

Col.....

[AstralTraveller]

Marty and Col are on the right track - but no cigar.

Col, ice made from ordinary tap water floats in water (and whisky :)).

[AndrewJ]

One is made from heavy water

Andrew

[The_bluester]

Water ice and Dry ice? (Carbon Dioxide)

[AstralTraveller]

Is the correct answer. Congratulations, I owe you a Mars bar. :)

Yes, the normal ice cube is H2O and the other is D2O. Normal water has an atomic weight of 18 (16+1+1) but D20 has an atomic weight of 20 (16+2+2). Since both have the same number of molecules per mL the 'isotopically heavy' ice is also actually physically heavier. [I am assuming that the oxygen-16 : oxygen-18 ratio is normal but if it is also enriched then the ice would be even heavier.]

The photo was submitted on a mailing list in response to an request for a photo which demonstrates stable isotopes. There is another member of IIS who also measures stable-isotope ratios for a living so for him this would have been trivial and I think some others may also have a professional reason to understand this; they were the people who I wanted to stay mum.

Thanks to all who gave it a shot.

[The_bluester]

I wondered about that but don't know enough about heavy water without looking it up.

I was not sure on the dry ice (I know it does not float in water, been there done that for my 6YO when using it to strip sound deadening form a car) as I could not pick up from the image if there were CO2 bubbles coming from it.

Something learned on a Friday!

[GeoffW1]

Some other stuff:

Heavy water is poisonous when taken in large quantities, but not in a cupful.

Think how our world would be constructed if ordinary ice sank. This is another facet of the Goldilocks Enigma - "Why is the Universe so right (locally) for us to be here?"

I'm a devotee of that school which says we shouldn't be all surprised that it is, because if it was not, we would not be here to wonder at it. The Cosmos was first, we were second by a long way.

Cheers

[AstralTraveller]

And ultra-pure water is also bad for you if you drink too much. I think it washes electrolytes from your system. I'm not sure why heavy water would be poisonous. Presumably the slightly greater bond-energy of heavy water impedes or facilitates a biochemical pathway.

[doppler]

That's a cool experiment, now where do you buy heavy water from?

[Baddad]

What do you mean "no cigar"? Heavy ice is frozen heavy water. I know that it sinks in tap water. I stated "heavy ice" so as not to actually give it away.
Deuterium oxide. D2O as opposed to H2O

Cheers

[AstralTraveller]

It worked - you fooled me. :confused2: I think the 'LOL' threw me. Sorry. :( Have a cigar!

[iborg]

Where to buy is not hard, only $700 per liter

http://www.sigmaaldrich.com/catalog/product/aldrich/151882?lang=en®ion=AU (http://www.sigmaaldrich.com/catalog/product/aldrich/151882?lang=en&region=AU)

Don't drink too much.

We have some of this around for NMR work, doesn't get used much.

Philip

[AndrewJ]

Gday David

Sorry about that, i was semi joking ( leveraging off the heavy ice comment )
Being a Mech engineer, i knew they had to be of different densities, but didnt know you could actually buy "heavy water".

Andrew

[doppler]

"Where to buy is not hard, only $700 per liter"

The kids can look at the picture

[Baddad]

Thanks David, :)

I disguised it too well I suppose. It was meant not to give it away and I even fooled you. My Bad. LOL:lol::)

Cheers

[AstralTraveller]

Now let's get this straight. I told the person who knew the answer he was wrong. Then I told someone who didn't know the answer he was right. :question:

The next quiz is: spot the prize goose. :rolleyes:

[julianh72]

OK, ice made from heavy water would work, but a MUCH cheaper and easier way is to make ice from a saturated sugar or salt solution. Heavy water will cost you about $1 / mL - if you can find any.

When you dissolve sugar or salt in water, the density increases - the sugar / salt "fits in between" the water molecules, and the volume barely increases. Sugar is easier, because it will freeze in your normal freezer. Saturated salt water freezes at about -21 Celsius, which is a bit beyond the capacity of the average home freezer. If you put less salt in, the freezing point will be higher, but the density will be lower, so it may not sink. Saturated sugar water will still freeze at about -10 Celsius, so you can easily make nice dense sugar-ice cubes in your home freezer.

A neat party trick - make a tray of normal ice cubes and a tray of sugar water ice cubes, and put one of each into the drinks. The plain water cube floats, the sugar water cube sinks, and is perfectly safe to drink as it melts. (Please don't try this with a good single malt scotch though - save it for the soft drinks and cocktails!)

[Baddad]

Hi Julian,:)
I'm afraid I would have to disagree with that method. Its like putting a lead sinker in the ice cube. Its not just water any more.
Heavy water is still 100% water or near enough to it.

Cheers:)

[Baddad]

It worked - you fooled me. :confused2: I think the 'LOL' threw me. Sorry. :( Have a cigar!

Thanks David. But I don't smoke. :) :lol:

[AstralTraveller]

Actually both D2O and sugar solution demonstrate something scientific, whereas the sinker is trickery. The D2O is more 'exotic' in that it happens at the atomic level rather than molecular level, is more outside the realm of everyday experience and is certainly more expensive. Also, we all know about sugar solutions (generally we are too familiar with them ;)) but stable isotopes are something that, even though they are all around us and in us, are still outside most peoples knowledge. [Their use in science is also largely unknown.]



That is much cheaper than I would have expected. We pay in that range for ultra-high-purity nitric acid. Even a set of cartridges for water purification - so you can get water with nearly nothing in it - cost us about $2.5-3k a set. I remember being told about some exotic reagent that is $30k per litre but I can't recall what it is.

[ZeroID]

Aqua Regia ? The Acid that chews through glass ...:question: Sulfuric and Nitric Acid mixed...

EDIT: second thoughts ... HydroFlouric Acid ... real nasty stuff ..

[julianh72]

Printer ink cartridges cost almost that much!

When you work out the cost per litre it costs more than Chanel No. 5.

[julianh72]

I remember my Chemistry teacher back in High School used to tell the joke about the Chemist who spent 20 years searching for the perfect solvent (that would dissolve anything it came into contact with) - and then spent the next 20 years looking for something he could store it in.

[sjastro]

Cheaper than antihydrogen which is going at a cost of US $62.5 trillion dollars per gram.:thumbsup:

Steven

[andyc]

David's mention of fluorinating reminded me of this entertaining post (http://pipeline.corante.com/archives/2010/02/23/things_i_wont_work_with_dioxygen_di fluoride.php) in a series entitled "Things I won't work with". FOOF is extraordinary and not a little horrifying, and the few experimental scientists who've made it and played with it are surely insane... even in the chemical world :eyepop::scared3:

[OzStarGazer]

I remember we had this in school! But only theoretically, maybe because heavy water is so expensive?