Heavy Water - Periodic Table of Videos

okay so we're going to do an experiment today that Martin Polyakov has been on us to do for a while so we finally finally going to get it get around to doing it he's very excited about it and what we're going to talk about is is a deuterium oxide okay so GT reom oxide is often referred to as heavy water most elements exist in more than one form which are chemically identical but where the atoms weigh different amounts and the difference between these different forms which are called isotopes is by far the biggest for hydrogen so it's heavy water so water is h2o as which are everyone knows and G Tyrion oxide is d 2o so hydrogen normally has one proton but a second form of hydrogen called deuterium has Neutron as well the neutron has the same mass as the proton but is electrically neutral it doesn't have a positive or negative charge the proton has a positive charge so you can add this without affecting the atom you still have just one electron so it's just like hydrogen but now you can see it weighs twice as much so hydrogen is just proton with a little electron buzzing around it if you like NGT reom is a proton and a neutron with an electron buzzing around it in the universe and on the earth about one atom in every seven thousand of hydrogen is in this heavy for deuterium this means that if you are an average weight our belt of about 70 kilos and making the assumption of about how much water is in your body somewhere between 6 to 8 grams of the water in your body is in fact heavy water which contains deuterium instead of hydrogen Niels dug out a really old school sample of deuterium oxide so I like I like the box I finally worked out how to how to open it which is good and what we have is a really really old school song but look at the writing it's all kind of like on the list 1930s writing or something I'm not quite sure how old it is but it's so in really old Psalm of DTO and it's sealed in a glass ampule so that so that it kind of remains as it is in there where do you get all that stuff yeah so you can imagine water which is h2o has these heavier atoms of hydrogen which have their own chemical symbol so instead of being h2o it's now d2o and you can also and as in your body what you will have is just one hydrogen and one deuterium because you've got so much water and the hydrogen's and the yolks the hydrogens and the deuteriums can just switch around between one molecule another they feel really careful and do a careful separation process you can get pure D to O so today's grand experiment is we're going to make while we've made some ice cubes with normal water and some ice cubes with D to O okay so we got an ice cube tray which we're going to dig out in a minute and we've actually just made some normal ice cubes and what we're going to do is it's an experiment I've never I've never actually done before and we're going to see if the obviously you know that water to ice because it's less dense than water actually floats in water and we're going to look to see if we make D to Oh ice cubes where they will float in the water or not because dose of deuterium oxide is a bit denser than water heavier D does not appear on the periodic table but deuterium is used so much in all sorts of chemical experiments that it has its own simple in fact there is a third form of hydrogen which has two neutrons so it's weight of three units called tritium which has a simple tea but tritium is radioactive so it's not used very widely unless you're trying to make nuclear weapons and that's another story what we need to do first and is we need to get rid of all the eggs obviously is a lot of air dissolved in indeed in d2o in anything and so neil has degassed some d2o and some water for us so this is a vacuum pump here and what you can do is apply a vacuum to said liquid and pump out all of the air out of the out of the liquid so we're degassing it there we go so what happened was that the the air basically started to almost if you like boil out of the water for a long time I can't remember how long but more than 30 years it has always struck me that ice solid water is about ten percent lighter than all the liquid water that's why ice floats at the top of your drink or floats on the top of the pond in your garden okay so what we did was he made some ice cubes with the D gas water so these are the water ice cubes the colorless ones and what we did with the DTO ones just so we could see the difference is we put a little tiny bit of food coloring only a small amount so it shouldn't affect the experiment at all but just so we can see the difference okay so what we need to do now is filiz because with waters we'll get some water the question is since d 2o is of 10% heavier than h2o heavy ice solid d 2o should be just about the same density all but slightly heavier than liquid water so it might be that heavy ice should sink in liquid water in let ordinary water and I've always wondered what happens and I've never been able to do the experiment the one going to do is I hope this works Papa D - Oh ice cube in here and I'm hoping it sinks yeah I think that's sunk I now know that my colleagues have done it but I have no idea what happens my prediction and I've done lots of calculations is that it'll just sink but I might be wrong I might have gotten to include something in my calculation so what we've got is we've got ice in water here and ice is less dense than water so it's floating and in this one we've got the deuterium oxide ice so frozen deuterium oxide and that is denser than the water so it's sent to the bottom we did the experiment and the d2 ice did sink and it's ain't quite graduating yet but here's what happened over the course of the next hour as the d2o began to melt it gradually the cube began to rise towards the top of the water have you any idea why that would have happened I think what has happened is that the d2o molecules on the surface of the ice will have exchanged with hydrogen and I think also that the melting point of d 2o is different from that of ice so that you probably have some melting and reforming of the ice on the surface so that it gradually gets less dense and you've got to remember though if you have a cube most of the mass is near the outside so if you change the composition of the ice on the outside it makes a big difference for the total weight of the block obviously is quite a problem how do you make d2 oh because normally the deuterium in the water is diluted by a factor of seven thousand which for chemists is really pretty dilute you

Channel: Periodic Videos

Views: 676,186

Rating: 4.9498897 out of 5

Keywords: heavy, water, deuterium

Id: hUVzb0fzHsk

Length: 8min 25sec (505 seconds)

Published: Tue Jun 08 2010

Reddit Comments

[u/myarlak]

Neat experiment, I have a couple of issues with it though. A) they should have done at least 1 cube of D2O with no coloring and 1 of H2O with coloring as controls B) the professor needs to stop saying the D2O ice will sink because it is heavier, it is sinking because D2O ice is more dense than water. C) I don't like his explanation of why the ice gradually rises to the top, I think the correct answer would be, as the D2O ice melts it dilutes the beaker of water with D2O, thus making it more dense until it reaches a the point where the beaker of H2O/melted D2O is more dense than the D2O ice cube and thus the cube rises to the top.