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What properties are desirable in a recrystallization solvent

The principle behind recrystallization is that the amount of solute that can be dissolved by a solvent increases with temperature. In recrystallization, a solution is created by dissolving a solute in a solvent at or near its boiling point.

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At this high temperature, the solute has a greatly increased solubility in the solvent, so a much smaller quantity of hot solvent is needed than when the solvent is at room temperature. When the solution is later cooled, after filtering out insoluble impurities, the amount of solute that remains dissolved drops precipitously.

At the cooler temperature, the solution is saturated at a much lower concentration of solute. The solute that can no longer be held in solution forms purified crystals of solute, which can later be collected. Recrystallization works only when the proper solvent is used.

The solute must be relatively insoluble in the solvent at room temperature but much more soluble in the solvent at higher temperature. At the same time, impurities that are present must either be soluble in the solvent at room temperature or insoluble in the solvent at a high temperature.

Recrystallization

For example, if you wanted to purify a sample of Compound X which is contaminated by a small amount of Compound Y, an appropriate solvent would be one in which all of Compound Y dissolved at room temperature because the impurities will stay in solution and pass through filter paper, leaving only pure crystals behind. Also appropriate would be a solvent in which the impurities are insoluble at a high temperature because they will remain solid in the boiling solvent and can then be filtered out.

When dealing with unknowns, you will need to test which solvent will work best for you. According to the adage "Like dissolves like," a solvent that has a similar polarity to the solute being dissolved will usually dissolve the substance very well.

In general, a very polar solute will easily be dissolved in a polar solvent and will be fairly insoluble in a non-polar solvent. Frequently, having a solvent with slightly different polarity characteristics than the solute is best because if the polarity of the two is too closely matched, the solute will likely be at least partially dissolved at room temperature. There are five major steps in the recrystallization process: dissolving the solute in the solvent, performing a gravity filtration, if necessary, obtaining crystals of the solute, collecting the solute crystals by vacuum filtration, and, finally, drying the resulting crystals.

Figure 1. Hot gravity filtration. If crystals don't form upon slow cooling of the solution to room temperature there are a variety of procedures you can perform to stimulate their growth. First, the solution should be cooled in an ice bath. Slow cooling of the solution leads to slow formation of crystals and the slower crystals form, the more pure they are. Rate of crystallization slows as temperature decreases so cooling with an ice bath should only be used until crystals begin to form; after they do, the solution should be allowed to warm to room temperature so crystal formation occurs more slowly.

If no crystals form even after the solution has been cooled in an ice bath, take a fire polished stirring rod and etch scratch the glass of your beaker. The small pieces of glass that are etched off of the beaker serve as nuclei for crystal formation. If crystals still do not form, take a small amount of your solution and spread it on a watch glass.

After the solvent evaporates, the crystals that are left behind can serve as seeds for further crystallization. Both these methods of nucleation i. Crystals will not form if there is a large excess of solvent. If no crystals form with the methods already discussed, a portion of the solvent may need to be removed.

This can be accomplished by heating the solution for a period of time in order to evaporate some solvent. The new, concentrated solution, should be cooled, and the previously mentioned methods to stimulate crystallization should again be attempted. Another potential problem in recrystallization is that the solute sometimes comes out of solution in the form of an impure oil instead of forming purified crystals. This usually happens when the boiling point of the solvent is higher than the melting point of the compound, but this is not the only scenario in which this problem presents itself.

If this begins to happen, cooling the solution will not stimulate crystallization, it will make the problem worse. If an oil begins to form, heat the solution until the oil portion dissolves and let the whole solution cool. As the oil begins to form again, stir the solution vigorously to break up the oil.

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The tiny beads of oil that result from this shaking may act as the nuclei for new crystal formation. Wired Chemist.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. Chemistry Stack Exchange is a question and answer site for scientists, academics, teachers, and students in the field of chemistry.

It only takes a minute to sign up. The compound in question is acetanilideand the solvents in question are: water, ethanol, and ethyl acetate.

I was thinking all three would be suitable since upon experimentation, acetanilide dissolved in all three solvents when heated. Is it possible to rank the suitability?

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As, well could someone provide an explanation as to why one is more suitable than the other? The ideal properties for a recrystallization solvent are that the compound of interest is soluble at high temperature but insoluble at low temperature. You have addressed the first part, so you just have to assess the second part.

Given that acetanilide is a non-polar compound, I would expect that it would have the lowest solubility in the most polar solvent. For this reason, water is probably the best, then ethanol. I would expect acetanilide to be readily soluble in ethyl acetate at room temperature, making it unsuitable for this recrystallization. It's not enough to be soluble. You want a solvent to have high solubility at high temperature, plus you want to have low solubility of the solute at low temperature.

Moreover, in an ideal world, you'd like the solubility of any impurities to remain higher than the target compound i. The first two are absolutely necessary to rank different solvents. The third is useful, but sometimes hard to know completely.

Acetanilide is readily soluble in ethanol at room temperature. So we can not use the ethanol as a solvent for acetanilide recrystallization. But it can soluble in water when heating. Therefore, water is the beat solvent for acetanilide.

Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. What would be the most suitable solvent for a single-solvent recrystallization? Ask Question. Asked 5 years, 11 months ago. Active 2 years, 9 months ago. Viewed 25k times. Geoff Hutchison Siddart Fredrick Siddart Fredrick 1 1 gold badge 4 4 silver badges 7 7 bronze badges.

Active Oldest Votes.No it is not. Selecting a proper solvent for recrystallization can be somewhat of an art, and improves with practice. You want a good solvent to have good solubilities of all components at higher temperature, unless they are insoluble impurities, then they are simply filtered off when hot. Then as you slowly cool the solution you want the product to start to crystallize out, while the impurities remain in solution.

The slower the product crystallizes out the higher the purity will be. So you want the product to start to crystallize when the solution is still warm.

That way, product will come out pure, and impurities will still be in solution. Then you cool the mixture down and filter off the product.

what properties are desirable in a recrystallization solvent

And good chemists will do many small scale recrystallization attempts at a very small scale, perhaps in a test tube, to see which solvent works best.

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what properties are desirable in a recrystallization solvent

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Video of ICE agents stopping Black jogger. Small town in Texas unites for justice for Jonathan Price. Answer Save. A good solvent for recrystallization must: 1.

what properties are desirable in a recrystallization solvent

Recrystallization Solvent. Maria Lv 4. This Site Might Help You. RE: What properties are desirable in a recrystallization solvent?What properties are necessary and what properties are desirable for a solvent to be well suited for recrystallizing a particular organic compound? That the product you want is insoluble at room temperate but then heated is completely dissolves your product while the impurites are dissolved into it at much lower temperatures, ideally room temperature.

A general rule to bear in mind when choosing recrystallisation solvents is that 'like dissolves like'. So, Aspirin and Ethanol share no similar functional groups, whereas, Aspirin and Ethyl Acetate both contain Ester bonds.

Due to this, Aspirin dissolves much more readily in the Ethyl Acetate than in the Ethanol. If Ethanol is used, there is a chance that not all of the Aspirin will dissolve. Hope this helps :. Trending News. Lucille Ball's great-granddaughter dies at A warning sign for Trump at The Villages in Florida.

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What properties are desirable in a recrystallization solvent?

Answer Save. Mr Hex Vision Lv 7. The main properties for a solvent for recrystallizing is That the product you want is insoluble at room temperate but then heated is completely dissolves your product while the impurites are dissolved into it at much lower temperatures, ideally room temperature.

Other than that, non-toxic, cheap solvents with middle range evaporating points are usefull. Still have questions? Get your answers by asking now.A good solvent for recrystallization depends entirely on the polarity of the solid you're trying to purify.

For example sodium chloride readily dissolves in water whereas naphthalene dissolves only in nonpolar solvents like hexane. To select a good solvent first consider the polarity of the compound of interest and pick a solvent that has the potential to dissolve it. Next suspend the solid in that solvent.

You must pick another solvent if the solid completely dissolves in the selected solvent. Heat the mixture while stirring. If you reach the boiling point of the solvent and the compound hasn't dissolved, you must find a different solvent or add more of the solvent you are currently using.

If your solid completely dissolves without too much of the chosen solvent, you have yourself a good solvent for recrystallization.

To continue with the recrystallization simply allow the solvent to cool and your solid should precipitate out in the form of crystals. Put it in an ice bath to assist with the precipitation. The latter technique can lead to small crystals or powder. The best way to remedy this is to do a slow recrystallization. To do this you must use two solvents that will evaporate over a long period of time.

One solvent must be very volatile and must be able to easily dissolve your compound at room temp. The other must be less volatile and your compound must be insoluble in this solvent. Note that this solvent must have the potential for dissolving the impurities in your compound. To perform the recrystallization, dissolve your compound in the "good" solvent and then add about the same amount of the "bad" solvent.

Over a period of time, the "good" solvent should evaporate leaving your crystallized product in the "bad" solvent without any impurities. Solvent for recrystallization will depend on the state that an element is in. If the element or compound is solid NaCl would work a solvent. The coolness of the solution causes recrystallization.No that is not. Then as you slowly cool the answer you choose the product to start to crystallize out, on a similar time as the impurities stay in answer.

The slower the product crystallizes out the better the purity would be. That way, product will pop out organic, and impurities will nevertheless be in answer. And stable chemists will do many small scale recrystallization tries at an exceedingly small scale, maybe in a try tube, to work out which solvent works proper. Trending News. Lucille Ball's great-granddaughter dies at Virginia health officials warn of venomous caterpillars.

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Many bottled water brands contain toxic chemicals: Report. Cuban shares update on Delonte West's recovery. Video of ICE agents stopping Black jogger. Small town in Texas unites for justice for Jonathan Price. Answer Save.

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Favorite Answer. Look at chlorine, it recrystallizes back if left in the air. Still have questions? Get your answers by asking now.No it is not. Selecting a proper solvent for recrystallization can be somewhat of an art, and improves with practice.

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You want a good solvent to have good solubilities of all components at higher temperature, unless they are insoluble impurities, then they are simply filtered off when hot.

Then as you slowly cool the solution you want the product to start to crystallize out, while the impurities remain in solution. The slower the product crystallizes out the higher the purity will be.

what properties are desirable in a recrystallization solvent

So you want the product to start to crystallize when the solution is still warm. That way, product will come out pure, and impurities will still be in solution. Then you cool the mixture down and filter off the product.

Solubility of organic compounds - Structure and bonding - Organic chemistry - Khan Academy

And good chemists will do many small scale recrystallization attempts at a very small scale, perhaps in a test tube, to see which solvent works best. Answer Save. A good solvent for recrystallization must: 1. Recrystallization Solvent. Maria Lv 4. This Site Might Help You. RE: What properties are desirable in a recrystallization solvent? Still have questions? Get your answers by asking now.


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