# Tag Info

20

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 the sense that it can get so viscous as to appear solid, without affecting its status of being a supersatured solution, and undergoes glass transition). https://...

17

Generally speaking, the best solvent will be dependent on the impurity that you are trying to remove. The solvent must dissolve both the desired compound and the impurity at a high temperature, but only the desired compound at lower temperatures. The solubility product of the impurity, as well as the common ion effect should both be taken into ...

16

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 temperature. Different description, same fact. What makes this seem different from e.g. a salt water solution is that the molten (i.e. non-crystalline) sugar is fully ...

15

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 : $$\ce{2 CuSO_4 + 2 Na_2CO_3 + H_2O -> Cu(OH)_2·CuCO_3 + CO_2 + 2 Na_2SO_4}$$ This forms some bubbles of $\ce{CO_2}$ as you have seen. And it produces a strange precipitate of the so-called basic copper carbonate, $\... 7 I think the most specific you can get on this phenomenon is nucleation , specifically heterogenous nucleation / surface nucleation. The rough surface formed creates scope for nucleation to occur, and this creates the crystals. I don't think there is a specific name for this technique as a lab tenchique . 7 Even if there is a method to extract salt from food, specially from apple crumble, it’ll probably ruin it. The simplest way I can think of doing this is dissolving the apple crumble in water and blending it. Filter it and then boil the filtrate. Given that every solid ingredient but salt is organic, when all the water boils off you should be left with salt ... 6 Spray it as a fine mist into a drying chamber - the solvent will evaporate and you are left with a powder. No chemical involved though, but still process chemistry. 6 Armarego's Purification of Laboratory Chemicals suggests using dichlormethane–hexane pair instead of ethanol–water; it also lists crystallization from warm ethyl acetate, ethanol or petroleum ether as alternative [1, p. 342]. Dibenzalacetone [DBA, bda, trans-trans-1,5-diphenyl-1,4-dien-3-one, 1,5-(bisphenyl)-penta-1E,4E-diene-3-one] [538-58-9]$\ce{...

6

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 (Ref.1): A cooled solution of 100 g. of sodium hydroxide in 1 l. of water and 800 cc. of alcohol (Note 1) is placed in a 2-l. wide-mouthed glass jar which is ...

5

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 using a fridge, you'll still lose more than half of the product, which is quite a bad business. Industrial process relies on evaporation, I think. Sugar is ...

5

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 supersaturated solution.

5

Crystallization is rightly called by you a process. Simplified, there are two steps to be considered: Nucleation and crystal growth. For the sake of simplification, let me consider the crystallization of a molecular compound in absence of ionic charges. Nucleation refers to the initial stage, where once isolated molecules of the dissolved substance ...

4

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 salt (ammonium sulfate is especially good for this purpose) reduces the solubility of the protein in water, causing it to precipitate or crystallize out. ...

4

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 and amorphous water ice. Metallic glasses may have improved wear and corrosion resistance over a crystalline alloy. One interesting intermediate form is a ...

4

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 you produce will be impure and sticky; the methyl benzoate and pyridinium hydrochloride will not pass through the filter but will bind to the product crystals.. ...

4

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 above $\pu{70 ^\circ C}$ in a form of melt, and above $\pu{120 ^\circ C}$ – as a polycrystalline solid material. I finally got across to suitable references to ...

4

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 finds the experimentally determined phase diagram. With enough water in the mix, one proceeds smoothly from the pure hydrazine melting point down to a slight ...

3

Typically, you will want to make sure that your solution is saturated. Don’t add a specific, certain amount; rather, add the solid to hot distilled water until it actually won’t dissolve any more. Then quickly filtrate the hot solution through a hot funnel (don’t burn yourself though, please). Let this filtered solution cool down and you should obtain ...

3

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 ingredients, such as carbohydrates. According to the manufacturer, 100 mL of Red Bull, a popular brand, contain 11 g sugars and 32 mg caffeine. In order to ...

3

Choosing a recrystallization solvent is as much an art as a science, even when you know what the substance is. Without knowing, it is a matter of making educated guesses. You want a solvent where it is much more soluble in the hot solvent than in the cold. Given that this is a lab exercise, we can assume that these are common substances. So, the one that ...

3

This is a very broad and very interesting question, but the basic point is: polymorphs exist either because their formation is controlled by kinetics (rather than thermodynamics, which would favor the most stable phase), or the thermodynamic equilibrium between the various polymorphs is influenced by the synthesis conditions (temperature, pressure, presence ...

3

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 couple of grains of the pure substance you are creating is added to act as a nuclei for crystallisation to take place upon.

3

To answer part 1 of your question: It is correct to call the change form solid to gas below the equilibrium vapor pressure sublimation. And there is no separate term for vaporization of a solid above the equilibrium vapor pressure; it is still sublimation. Similarly, a boiling liquid is still perfectly correctly said to be evaporating. To answer part ...

3

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 occupies positions in the crystal lattice); occlusion (impurity is physically captured within the crystal as it has been growing); adsorption (impurity is adsorbed ...

3

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 finding a solvent in which the compound of interest is sparingly soluble at room temperature, but highly soluble at elevated temperature such that slow cooling ...

3

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$^\circ$. Alternatively, cryst[alise]d from aqueous EtOH, as the trihydrate. This material can be converted to the anhydrous salt by heating slowly in a porcelain, nickel or ...

3

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 function of temperature. In a certain temperature range, the solution will always be saturated with respect to one substance and unsaturated with respect to the ...

3

I found an old research paper which states that hydrazine forms monoclinic crystalline structure in molecule pairs. Given the ongoing discussions on whether a rocket-fuel mixture separates or not as it cools, I'm adding this paper which says hydrazine monohydrate forms trigonal crystals. I admit to massive ignorance as to the exact compounds used in ...

3

What happened was very simple. I've been duped. The seller sold me (intentionally or not) sodium dichromate and not potassium dichromate, or at least very contaminated with sodium dichromate. According to online source (https://en.wikipedia.org/wiki/Solubility_table#S), the solubility of sodium dichromate in water is about 198g/100ml of water at 30°C, and ...

3

Shea butter is a complex combination of esters: (Wikipedia). The overall ratio of oleic to stearic acids is about 2/1, but statistically, there will a little of the high melting stearic, more of the 2 stearic to 1 oleic; much more of the 2 oleic to 1 stearic, and a lot of all oleic ester. The melting point of shea butter is low (body temperature) and so if ...

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