22
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Is honey really a supersaturated solution? Does heating to un-crystalize redissolve it or melt it?
Honey is indeed a complex mixture containing more than hundred compounds.
As for Wikipedia and depending on the point of view it is
a supersatured liquid solution
a viscous supercooled liquid (in ...
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18
votes
Is honey really a supersaturated solution? Does heating to un-crystalize redissolve it or melt it?
Melting and dissolving are all the same when you look at mixtures close to saturation.
You can say water lowers the melting point of the sugar, or that the solubility of sugar increases with ...
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17
votes
Accepted
What is this copper compound I made?
There are two surprising phenomena in this experiment.
First : $\ce{CuSO_4}$ reacts in a unusual way with $\ce{Na_2CO_3}$. The equation is : $$\ce{2 CuSO_4 + 2 Na_2CO_3 + H_2O -> Cu(OH)_2·CuCO_3 +...
- 25.6k
14
votes
Accepted
What factors promote honey's crystallisation?
The decisive factor is the plant origin of honey. The major components ( reportedly by some beekeeper books of my passed away father ) have ratio glucose : fructose about 1:1 to 1:1.7. Glucose ...
- 36k
12
votes
How can I roughly measure a fraction of a gram?
You ask:
Can I roughly get the weight that a fraction of a gram without buying a scale just for this crystal making kit?
Absolutely.
You're in Japan. You have access to Japanese coins which ...
- 10.5k
10
votes
Why is it so difficult to crystallise anything in a glass capillary?
It has not (so much) to do with the shape of your container, rather than the accessible volume and thus, probability of events. To quote Meldrum and O'Shaughnessy:
"Nucleation in small volumes ...
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8
votes
Why is sea salt coarse?
The method of production of sea salt usually involves bulk evaporation of seawater. This allows the salt to crystallise and due to it's bigger size it is sold without much processing. On the other ...
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8
votes
How can I roughly measure a fraction of a gram?
I think the mass of the seed is not critical. But you can create your own scale - or even better, involve the son in its creation.
You can create a 2-shoulder scale, with 2 stuff holders hanging at ...
- 36k
7
votes
Recrystallisation of dibenzylideneacetone
Armarego's Purification of Laboratory Chemicals suggests using dichlormethane–hexane pair instead of ethanol–water; it also lists crystallization from warm ethyl acetate, ethanol or petroleum ether as ...
- 37.2k
7
votes
Recrystallisation of dibenzylideneacetone
Ethyl acetate is the solvent of choice in Org. Synth. 1932 article. The procedure was submitted and checked. The following is the the full procedure stated in Organic Syntheses.; Collective Volume (...
- 38.6k
7
votes
Why is sea salt coarse?
Because it is not ground as fine , unless a customer wants finely ground sea salt. It is passed over screens to separate it into sizes after grinding, just like table salt. Fun fact ; table salt that ...
- 3,651
7
votes
How can I roughly measure a fraction of a gram?
If you know the density of the crystal (usually a salt), you can estimate the mass of a crystal based on its volume, i.e. by measuring the lengths of its sides.
For example, table salt (sodium ...
- 4,337
6
votes
Can uranium be used to color aluminium oxide based gemstones, and/or diamonds?
It's not quite alumina, but uranium(VI) oxide compounds have been used to color glass:
Oxides and uranates of uranium(VI) have been used in the past as yellow ceramic glazes as in Fiesta and to make ...
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5
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Accepted
Why is the addition of methanol during the prepartion of the liquid crystal cholesteryl benzoate necesary
Pyridinium hydrochloride and methyl benzoate are both soluble in methanol and thus will be washed through the filter leaving behind clean cholesteryl benzoate. If you don't use the methanol the solid ...
- 20.6k
5
votes
Accepted
Why are 'table salt and sugar are both terrible candidates for recrystallization'?
The solubility of $\ce{NaCl}$ has very poor temperature dependency. If you dissolve it at $100^\circ\rm C$ and precipitate at $20^\circ\rm C$, you'll essentially lose about 35 g to purify 3 g. Even ...
- 30.7k
5
votes
Accepted
Why do we scratch the walls of test tube in test for magnesium or calcium basic radicals?
Scratching causes microscopic shards of glass to chip off the scratched surface which can break the surface tension of the liquid, allowing the solute to precipitate/crystallize from of the ...
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5
votes
Accepted
Does hydrazine crystallize when freezing?
I would take a different position on answering the question, and look at the water-hydrazine binary phase diagram. Looking at J. A. McMillan and S.C. Los, J. Chemical Physics 42(1) 160-161 (1965) one ...
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5
votes
Accepted
Are precipitation and crystallization both analogous between Chemistry and Meteorology?
In chemistry, on Earth in gravity, if a material from solution conformally, over all surfaces vertical and horizontal (e.g. the sides as well as the bottom of a container) is that still sometimes ...
- 37.3k
4
votes
Would a melted crystal recrystallize back into the same lattice structure when frozen?
If cooling is rapid enough, then crystals don't have time to form, so the substance may be amorphous or glassy (though there may be some localized structure). For example, there are metallic glasses ...
- 27.4k
4
votes
Accepted
Saturation of multiple solutes
Different solutes in the same solution indeed can affect each others' solubility. One example where this effect can be used to advantage is the "salting out" of a protein from water solution. Adding a ...
- 9,156
4
votes
What is the correct name for this lab technique in crystallization?
In my experience, my senior lecture has called this method 'scratching' and said that this is a widely used term.
The term nucleation is used to aid the description of the technique 'seeding' where a ...
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4
votes
Accepted
Crystallization in a solution of 2 or more solutes
When the solution contains several substances, it is very often possible to achieve their separate sequential crystallization due to the different nature of the solubility of the substances as a ...
- 37.2k
4
votes
Recrystallizing Sodium Acetate from solution
The Purification of Laboratory Chemicals by Perrin and Armarego states about sodium acetate this procedure:
Cryst[alise]d from acetic acid and pumped under vacuum for 10h at 120$^\circ$.
...
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4
votes
Crystallization of zinc sulfate monohydrate
TL; DR: obtaining a reasonably big single crystal of $\ce{ZnSO4 * H2O}$ seems to be a tricky task, whereas one can easily obtain $\ce{ZnSO4 * H2O}$ as a result of thermal dehydration of heptahydtare ...
- 37.2k
4
votes
How to make pyramid-shaped NaCl salt crystals
TL;DR: Use 10-20% urea solution for octahedral crystals and a water-ethanol mix for pyramidal crystals.
There is no universal method to predict and to control crystal habits. Very often the ...
- 37.2k
4
votes
Recovery of Urea from aqueous solution
@MatNX, as you state, "sensitive technology and high temperatures are typically a very bad match." However, there is no magic way to "make" cold, only to move heat from one ...
- 27.4k
3
votes
Solvent for recrystallization of benzoic acid?
It can be difficult to guess at what a given compound will crystallise out from, and often there is a lot of trial and error involved.
Generally, the most 'common' type of recrystallisation involves ...
- 17k
3
votes
Why is the solid product washed with ice-cold solvent during in the last stages of recrystallisation?
Possible sources of impurities in the recrystallization process can be described in terms of phenomena occuring during coprecipitation and which are the basis of gravimetry:
inclusion (impurity ...
- 37.2k
3
votes
Sublimation and recrystallization of caffeine
This sounds like a nice project.
For the purification of caffeine, sublimation in vacuum and recrystallization from ethanol are both conceivable.
But first you have to separate it from the other ...
- 43.7k
3
votes
Accepted
What is the difference between hexanes and petroleum ether
Petroleum ether:
This is a mixture of a lot of different compounds (aliphatic hydrocarbons in this case) that as a mixture have a boiling point within a specified range. The contents are dealt with as ...
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