Atthe Renaissance fair a few years back I was watching a smith forge metal into shapes. During this time a very odd question came to me. I was wondering what the furnace was made of. My logic stated that whatever the furnace was made of must have a higher melting point than the materials he was melting. This quickly turned into an elemental arms race resulting in an odd question of how do we melt stuff like refractory metals (more specifically the one with the highest melting point) so we can melt other things inside of it.
Tungsten's melting point of 3422 C is the highest of all metals and second only to carbon's, for which melting occurs only at high pressure (there's no standard melting point). This is why tungsten is used in rocket nozzles and reactor linings. There are refractory ceramics and alloys that have higher melting points, notably $\ceTa4HfC5$ with a melting point of 4215 C, hafnium carbide at 3900 C and tantalum carbide at 3800 C.
Carbon cannot be used to hold molten tungsten because they will react to form tungsten carbide. Sometimes ladles and crucibles used to prepare or transport high melting point materials like tungsten are lined with the various higher melting ceramics or alloys. More typically tungsten and other refractory materials are fabricated in a non-molten state. A process known as powder metallurgy is used. This process uses 4 basic steps:
Blacksmiths avoid melting their forges because the "heat" that can melt or oxidize iron and steel is actually contained in a ball in the center of the coal. In fact, maintaining coal "structure" is an important skill in blacksmithing.
To clarify better, imagine a hollow in the center of a pile of coal. This is where the temperatures rise past 2000 F, since the heat reflects back in on itself due to the coal molding into a refractory ball of sorts.
One could melt them floating on a pool of high-boiling point denser metal, or in space where they can readily be contained. Or one could create a thick actively cooled shell and melt them inside it, melting part of the shell as well. Finally, it's probably not very practical, but one could use an air jet to keep then suspended away from other matter and then melt them with lasers or superheated air.
The first is to use an actively cooled vessel to hold the metal and a method of getting energy into the metal not based on the heat of the crucible. Many metal-vapour reactions (used for small scale chemistry research) do this and provide sufficient energy to vaporise even refractory metals using electron guns. See Malcolm Green's site (and this entry "The synthesis of the first zerovalent compounds of the early, refractory transition metal via the development of the electron-gun metal vapour synthesis experiment").
The other method is to use inductive heating of the metal. This can sometimes work even without a vessel at all as a suitable inductive coil will levitate the lump of metal and the induced eddy currents will dump enough energy into it to melt it. There are plenty of youtube videos of this with non-refractory metals such as aluminium but the principle should still work for high melting metals.
Figuring out the order of boiling points is all about understanding trends. The key thing to consider here is that boiling points reflect the strength of forces between molecules. The more they stick together, the more energy it will take to blast them into the atmosphere as gases.
Compare the different butane alcohol derivatives shown below. Molecules of diethyl ether, C4H10 O, are held together by dipole-dipole interactions which arise due to the polarized C-O bonds.
Still, the attractive forces in butanol pale in comparison to those of the salt sodium butoxide, which melts at an extremely high temperature (well above 260 C) and actually decomposes before it can turn into a liquid and boil.
Then think about butane, C4H10, which contains no polar functional groups. The only attractive forces between individual butane molecules are the relatively weak Van der Waals dispersion forces. The result is that butane boils at the temperature at which water freezes (0 C), far below even that of diethyl ether.
Well, the key force that is acting here are Van der Waals dispersion forces, which are proportional to surface area. So as you increase the length of the chain, you also increase the surface area, which means that you increase the ability of individual molecules to attract each other.
To take another intuitive pasta example, what sticks together more: spaghetti or macaroni? The more spherelike the molecule, the lower its surface area will be and the fewer intermolecular Van der Waals interactions will operate. Compare the boiling points of pentane (36C) and 2,2-dimethyl propane (9 C).
In summary, there are three main factors you need to think about when confronted with a question about boiling points. 1) what intermolecular forces will be present in the molecules? 2) how do the molecular weights compare? 3) how do the symmetries compare?
If your compound is water soluble and you are drying it through rotary evaporation / distillation, the acetic acid and water will evaporate at similar rates. At the end you will have NaOH / NaOAc salts however.
Thank you James.
Remaining with the same example (in the extremes as you said), if I make the solution of diluted acetic acid completely boil in a beaker as to remove water, what will remain in the beaker? Acetate salts?
I want to know, how water content in crystallized substance affects its melting point. The main reason behind this question is that after synthesizing benzoic acid, its melting point was found to be high, i had to give certain errors that increase the % yield. So, to verify that water was present in the solid crystals, If i can justify that melting point was higher than expected due to presence of water, the error of increased % yield will be justified
Hey there, just wanted to stop by to say how much I appreciate this website. You have an exceptional ability to present material in a concise, understandable fashion. I wish you were the author of my organic chemistry book or my professor, because this year I have been teaching myself organic chemistry using your website and my textbook (lecturer is awful) and received an A+ in ochem 1. Thank you!
Why does NO2 have a greater boiling point than SO2? Both are polar, dipole-dipole interactions, but SO2 has a greater dipole moment, greater molar mass, and greater surface area. I know NO2 is a radical, does that affect boiling point?
do we only can compare the molecular size and molecular shape for the similar molecules or we can compare the size and shape for molecules with different functional groups ? for example can i compare the size and shape of pentanoic acid with heptane ?
Hi thanks for this info helps a lot but I have a question. It concerns organic compounds. Say you have a ketone such as heptanone. So the boiling point of this compound should be relatively high because it has a large surface area and it is a polar molecule so there are dipole -dipole forces present. Now take a alcohol that is a shorter chain such as propanol. Alcohol should have a higher boiling point because it has a hygrogen bond. But the propanol molecule is a much shorter chain so it has a smaller surface area than the heptanone. So how can we work out which one has a higher boiling point? (In this case heptanone has a higher boiling point than propanol but I would like an explanation as to why.)
this was quite insightful, but i have a problem i was given a question to compare pentane and diethyl ether. Based on the information i have seen it looks like pentane has a higher boiling point than di-ethyl ether, based on actual BP but your information tells me that it should be otherwise as diethyl ether has dipole-dipole interactions and pentane has van der waal forces. Could you clear up for me which should actual have the higher BP and give a reason for the answer?
Good question. It is likely due to the greater electronegativity of oxygen (3.4) versus nitrogen (3.0) leading to a larger dipole, which means that the molecules will have a greater force holding them together.
How does branching affect melting point?
I get the fact that branching decreases bp because of the decrease in surface area, hence less opportunities for Van de Waals interactions. However, how does it work for melting point? When it is branched it is harder to stack, right? Then, a lower melting point?
Thanks! :)
There are different types of lattices. A lattice point is a point in any of these lattices. Lattices are used to describe highly ordered systems such as crystals and some supersolids. I am unsure whether lattices can only describe periodic systems (see quasicrystals). However, I will be assuming that we are talking about periodic lattices. I will also be assuming that we are dealing with crystals.
Bravais lattices are more mathematical and abstract than crystal lattices. They are pretty much the same as crystal lattices. Unlike the crystal lattice, however, lattice points in the Bravais lattice no longer represent a position of a particular atom. Instead a lattice point represents a position in which an atom can be placed. In other words, a lattice point in a Bravais lattice is a point, which is equal and indistinguishable from any other another point. What matters in a Bravais lattice are not the points themselves, but how they are arranged (i.e. symmetry).
The reciprocal lattice is the Fourier transform of either the crystal lattice or a Bravais lattice. More often than not, it is used to refer to the Fourier transform of the Bravais lattice. More of that is explained in Physics.SE. However, I personally think that this video explains it better. A lattice point here can represent an atom or a point, depending on the context.
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