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Questions tagged [recrystallization]

For questions related to dissolving and subsequently precipitating as substance. The purpose may be for purifying, creating polymorphs, or other reasons.

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Does hydrazine crystallize when freezing?

When discussing problems of keeping hydrazine from freezing on spacecraft we stumbled upon a question: can pure hydrazine separate through fraction-freezing from the stabilizing substances like UDMH? ...
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29 views

Why do you need to cool slowly in a re-crystallization experiment?

After saturating your solution, why can't you put in directly In an ice bath. Why should you cool to room temp before putting the solution the ice-bath?
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1answer
149 views

How does recrystallization work to purify if compounds have equal solubilities, but one is present in a greater quantity?

Every article or text I've read on crystallization states that it works by taking advantage primarily of differences in solubilities, but I've also been told that it can purify compounds with ...
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29 views

Readings about chiral resolutions at the undergraduate level

Does anyone know of a resource which clearly explains the scientific theory and experimental methods involved in chiral resolutions? I have access to the American Chemical Society, Tetrahedron, ...
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114 views

Why is recrystallisation used when filtration appears to be a better option?

Recrystallization: A solid containing the desired product and impurities are dissolved in a heated solvent. The reason this method works is because since the concentration of the desired product is ...
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0answers
810 views

How to make pyramid-shaped NaCl salt crystals

I'm attempting to make sea salt pyramids like the one below. I understand this needs to be evaporated at a reasonable speed to stop the crystals forming a cube, as the when formed quickly, the edges ...
3
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1answer
328 views

Questions regarding the preparation and recrystallisation of methyl 3-nitrobenzoate

I have a procedure for the synthesis of methyl 3-nitrobenzoate (via nitration of methyl benzoate): Weigh 2.0 g of methyl benzoate into a dry 50 cm3 conical flask. Add 4 cm3 of concentrated ...
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0answers
199 views

Multi-solvent recrystallization to extract solute from glycerol?

I have compound A contaminated with impurity B. Recrystallization in water would not yield pure compound A since impurity B is less soluble in it. The only solvent in which substances A and B have ...
4
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1answer
307 views

Crystallization of zinc sulfate monohydrate

I'm currently running an electrolysis experiment and I have a few questions regarding crystallization of zinc sulfate monohydrate $\ce{ZnSO4 * H2O}$. I have prepared a saturated solution of zinc ...
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0answers
99 views

What determines the maximum size of salt crystals as grown in flux growth?

Like many other children, I grew single crystal salt crystals in a salt solution. This is a common and fun experiment for children. However, with both this experiment, and with flux growth methods ...
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0answers
464 views

Scratching the inside of a flask to crystallize aspirin - what is it called and has it been scaled up? [duplicate]

I've just watched the Periodic Table of Videos on Aspirin and saw some "tricks" used to induce crystallization after the synthesis. Rapid heating with a heat gun followed by rapid cooling in ice was ...
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1answer
359 views

Crystallization in a solution of 2 or more solutes

This is a very basic question I found myself wondering. For simplicity's sake, we'll say it is a super saturated aqueous solution of an equivalent measure of sugar and salt. As the solution cools and ...
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2answers
360 views

Recrystallizing Sodium Acetate from solution

I made sodium acetate using the following reaction: $$\ce{NaHCO3 + CH3COOH ->CH3COONa + H2O + CO2}$$ The resulting solution of sodium acetate isn't pure, it has impurities. I want to crystallize ...
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1answer
59 views

Determining the chemicals in potash and crystallizing them

I have made potash by leaching wood ash in water. The potash in solution has a high pH indicating it is alkaline, and reacts with acetic and citric acid. Is there an easy way to determine the ...
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1answer
3k views

Solvent for recrystallization of benzoic acid?

Which is best solvent for recrystallization of benzoic acid? Water $\ce{CH3Cl}$ $\ce{CCl3COOH}$ $\pu{0.1 M}\ \ce{NaOH}$ I understand the solute/solvent should be soluble at ...
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0answers
4k views

Why is the solid product washed with ice-cold solvent during in the last stages of recrystallisation?

Why is the solid product washed with ice-cold solvent during in the last stages of recrystallisation? Is this to remove soluble impurities? (for example) Well, what if the impurities were also ...
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1answer
184 views

Why is the addition of methanol during the prepartion of the liquid crystal cholesteryl benzoate necesary

Here's one way to prepare cholesteryl benzoate crystals: Step 1 Dissolve 1.0 g of cholesterol in 3 cm3 of pyridine in a conical flask. Step 2 Add 0.40 cm3 of benzoyl chloride. Step 3 Heat the ...
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1answer
593 views

Recrystallization Process Questions [closed]

Should a crude compound should be dissolved completely in cold solvent and then heated up? I think non-polar solvents are best choice for recrystallization of polar compounds, no? Recrystallized ...
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1answer
147 views

DSC Metal hysteresis (melt/cryst)

So we were analyzing Polymers using DSC and calibrated the system using Indium. I expected it to be a single transition only as Indium only has 1 known crystal structure and as I never worked with DSC ...
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0answers
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Pressure/ vacuum on preciptation of a borax saturated solution

Trying to go back to my collage chem/physics. We put a supersaturated solution of borax on the stove. (heated water, added borax till it would not take more borax). Placed them under vacuum 15 inhg,...
5
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0answers
213 views

How do native sulfur crystals form?

I was visiting an elements exhibition in the Ulster Museum (Northern Ireland) and there were these native sulfur crystals on display. My question is how do sulfur crystals like these form in nature? ...
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0answers
2k views

Which of the following solvent pairs could be used in a solvent pair recrystallization?

The question relates to the recrystallization of 4-bromoacetanilide using 1:9 ethanol. I feel like I a missing some important details. I used this for reference on a). What would be the most suitable ...
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1answer
2k views

Is it correct to say that SOME iodine undergoes sublimation at 1 ATM

The triple point of Iodine occurs at 0.12 atm and at standard temperature it is a solid on the phase diagram. I understand that therefore, when heating iodine at 1 atm, it (at least some of it) will ...
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2answers
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What are disadvantages of using sublimation vs. recrystallization as a method of purification?

I can only think that a small sample can be sublimed while a bigger sample size can be recrystallized. Are there more?
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2answers
239 views

Making big crystals of oxalic acid crystals from powder [closed]

How to transform oxalic acid small crystals into large crystals?
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1answer
1k views

Sublimation and recrystallization of caffeine

I'm looking to do an extraction of caffeine from energy drinks. I want to use both sublimation and recrystallization in my experiment for advanced purity. My question is which should happen first, ...
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1answer
7k views

What is the difference between hexanes and petroleum ether

I'm trying to use hexanes as the nonsolubilizing recrystallization solvent in a multisolvent recrystallization (benzene is the solubilizing solvent) that requires an oxygen free atmosphere and hexanes ...
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1answer
439 views

Why are 'table salt and sugar are both terrible candidates for recrystallization'?

I received a comment on one of my other chemistry questions stating that table salt and sugar are both terrible candidates for recrystallization, albeit for different reasons. Why are salt and ...
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0answers
409 views

Why add specifically hot solvent during recrystallization procedures instead of heating it up after?

Recrystallization methods that I have seen online and in manuals involve adding a minimum amount hot solvent to the solid mixture. Is there a reason I should do this instead of adding an equivalent ...
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2answers
744 views

Calculating the theoretical percent purity of a recrystallization

The sample contains some percent A and some percent B with A being the majority. The solubility for both is given at two different temperatures. One where both are very soluble and one where both are ...
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2answers
798 views

Potassium Alum Crystals

This is a question regarding the crystallization of $\ce{KAl(SO4)2 . 12 H2O}$. I have an idea of what to do (I'll explain later in the explanation), but I would like to hear other suggestions encase ...
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0answers
84 views

What do DNA crystals look like?

I had about 5 ug DNA suspended in water, which I dried thoroughly in a vacufuge. I obtained a whitish crystal (very similar to table salt, although the structure seems uneven and it's hard to tell) ...
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1answer
148 views

Crystallization Process

In my lab, my teacher asked me to not cover the beaker or crucible during the crystallization process of different solutions (e.g, FeSO4, NaCl etc). But on the internet, on Youtube, I've come across ...
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1answer
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Why do we scratch the walls of test tube in test for magnesium or calcium basic radicals?

In test for calcium ion, we add ammonium carbonate in presence of ammonium hydroxide and then white precipitate (of $\ce{CaCO3}$) is formed which is dissolved in acetic acid and then reacted with ...
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1answer
113 views

Would a melted crystal recrystallize back into the same lattice structure when frozen?

Two things that I'm not sure about melted crystals: For a material that has only one possible crystal structure, would freezing cause it to recrystallize, or could it become amorphous upon freezing? ...
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0answers
45 views

Non-destructive solvents for cyan-salts

What dissolves cyan-salts (NaCN and KCN) without destroying them the way water does via hydrolysis? I have to make my own cyan-salts, so they're somewhat precious to me. Every time I have to ...
3
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1answer
1k views

Growing crystals that are in a magnetic field or subjected to an electric field

I know different crystals resonant at different frequencies but is it possible to grow crystal at a certain frequency. An example would be growing crystals using Epsom salt or Alum in a magnetic ...
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1answer
1k views

Tips for Improving Synthesis

I have already asked a similar question on titrations before. In a few months, I have a test on chemical synthesis. It is marked on the percentage yield, purity and crystal size of the product. I do ...
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2answers
359 views

Clarification on Recrystallization concept

Any help you could provide me would be greatly appreciated and I thank you for reading (even if you don't comment) I am in an organic laboratory and as a 3rd chemistry major these concepts usually ...
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1answer
138 views

Crystallization issue

For solid-liquid mixtures, cooling crystallization process can be used to separate the solute substances from each other. Assume that we have two salts that have very close solubility in a certain ...
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1answer
1k views

Saturation of multiple solutes

Can a liquid which is saturated with a single solute, dissolve a different solute, or is saturation a universal thing? I ask because I’ve seen that different solutes have different points (amounts) at ...
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2answers
607 views

Prevent crystal growth by adding a chemical to a solution?

If I have a solution of dissolved $\ce{NaCl}$ or sugar (or some other ionic compound), is there a chemical I could add to it that would prevent crystal growth if I boil it down? I'm looking for it to ...
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1answer
1k views

How to recrystallize boric acid into flakes?

I am putting 100 g of boric acid, 400 g of water and trying to crystallize at low temperature and letting cool slowly, however it recrystallizes as needle like texture. I need soft large crystals like ...
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3answers
17k views

What would be the most suitable solvent for a single-solvent recrystallization?

The compound in question is acetanilide, and the solvents in question are: water, ethanol, and ethyl acetate I was thinking all three would be suitable since upon experimentation, acetanilide ...
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2answers
5k views

Recrystallization and purification techniques for getting a pure sample

Could someone explain in detail as to why exactly recrystallization gives a more pure solid sample? As well as why is would be better 'technique' to allow for the crystal to form slowly? I was ...
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1answer
996 views

Recrystallization of two unknown compounds?

I managed to separate a binary mixture(in solid form) of two unknown substances into two individual solid compounds. For the separation, I used an acid-base extraction with dichloromethane, NaOH, and ...
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2answers
430 views

Best solvent for crystallization + mass recovered from crystallization + purity of the product

I have a chemistry final tomorrow and this question on my sample exam through me for a loop. I'm not entirely confident I can work out problems B and C, but those questions rely on the answer to A. ...
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1answer
296 views

Why polymorphs form?

We always hear about the different arrangements of molecules that lead to the formation of polymorphs, my question here is why would a polymorph form in the first place? The material was given enough ...
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1answer
812 views

Crystallization of solutions and liquids

The process of crystallization of a liquid or any solute occurs when its concentration exceeds the maximum concentration which the solvent can carry or when the temperature drops below the freezing ...
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3answers
246 views

Crystallization from a solution

I was wondering if there is any other way to crystallize materials from a solution other than using supersaturation? Thanks,