Recrystallization (chemistry)

→ Solvent added (clear) to compound (orange) → Solvent heated to give saturated compound solution (orange) → Saturated compound solution (orange) allowed to cool over time to give crystals (orange) and a saturated solution (pale-orange).
Crystallization of Ibuprofen in HCl(aq)
→ Solvent added (clear) to compound (orange) → Solvent heated to give saturated compound solution (orange) 
→ Second solvent (blue) added to compound solution (orange) to give mixed solvent system (green)
→ Mixed solvent system (green) allowed to cool over time to give crystals (orange) and a saturated mixed solvent system (green-blue).
→ First solvent added (clear) to compound (orange) → Solvent heated to give saturated compound solution (orange) 
→ Second solvent (blue) added to compound solution (orange) to give first mixed solvent system (green)
→ Volatile first solvent (clear) is removed (e.g. evaporation) from first mixed solvent system (green) to give a second mixed solvent system (dark-green)
→ Second mixed solvent system (dark-green) allowed to cool over time to give crystals (orange) and a saturated second mixed solvent system (green-blue).
→ Solvent added (clear) to a mixture of compound (orange) + insoluble substance (purple) → Solvent heated to give saturated compound solution (orange) + insoluble substance (purple)
→ Saturated compound solution (orange) filtered to remove insoluble substance (purple)
→ Saturated compound solution (orange) allowed to cool over time to give crystals (orange) and a saturated solution (pale-orange).
→ Solvent added (clear) to compound (orange) to give compound solution (orange) → Vessel sealed but a small hole allows solvent vapour (clear) to slowly evaporate from compound solution (orange) over time to give crystals (orange) and a saturated solution (pale-orange).
→ Solvent added (clear) to compound (orange) to give compound solution (orange) → Second solvent added (blue) to compound solution (orange) to give mixed solvent system (green)
→ Vessel sealed but a small hole allows solvent vapour (clear) to slowly evaporate over time to give crystals (orange) and a saturated mixed solvent solution (blue-green).
→ Solvent added (clear) to compound (orange) in first vessel to give compound solution (orange) → First vessel is placed in a second vessel contain second solvent (blue). The second vessel is sealed, the first vessel is also sealed, although a small hole in the first vessel is present. This hole allows volatile solvent vapour (blue) to slowly evaporate from second vessel and condensate (that is infuse) into the first vessel, to give a mixed solvent system (green) 
→ Over time this gives crystals (orange) and a saturated mixed solvent system (green-blue).
→ Solvent added (clear) to compound (orange) to give compound solution (orange) → Second solvent added (blue) carefully so that the two solvents do not mix.
→ The two solvents mix (diffuse) slowly over time to give crystals (orange) at solvent interface (green)
→ Solvent added (clear) to compound (orange) to give a compound solution (orange) 
→ Second solvent added (blue) to the second tube chamber 
→ The two solvents mix slowly over time, the mixing is slowed by a fine sinter separating the two solvent chambers, to give crystals (orange) at solvent interface (green) over time

Technique used to purify chemicals.

- Recrystallization (chemistry)

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Seed crystal

Small piece of single crystal or polycrystal material from which a large crystal of typically the same material is to be grown in a laboratory.

Single Crystal Growth Methods Tree Diagram

The placement of a seed crystal into solution allows the recrystallization process to expedite by eliminating the need for random molecular collision or interaction.

Solubility

Ability of a substance, the solute, to form a solution with another substance, the solvent.

Example for a dissolved solid (left)
Formation of crystals in a 4.2 M ammonium sulfate solution. The solution was initially prepared at 20 °C and then stored for 2 days at 4 °C.
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Dissolution of sodium chloride in water
Thermodynamic cycle for calculating solvation via sublimation
Thermodynamic cycle for calculating solvation via fusion

The technique of recrystallization, used for purification of solids, depends on a solute's different solubilities in hot and cold solvent.

Separation process

Method that converts a mixture or solution of chemical substances into two or more distinct product mixtures.

An ore extraction process broken into its constituent unit operations (Quincy Mine, Hancock, MI ca. 1900)

Recrystallization

Crystal

Solid material whose constituents are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions.

Crystals of amethyst quartz
Microscopically, a single crystal has atoms in a near-perfect periodic arrangement; a polycrystal is composed of many microscopic crystals (called "crystallites" or "grains"); and an amorphous solid (such as glass) has no periodic arrangement even microscopically.
As a halite crystal is growing, new atoms can very easily attach to the parts of the surface with rough atomic-scale structure and many dangling bonds. Therefore, these parts of the crystal grow out very quickly (yellow arrows). Eventually, the whole surface consists of smooth, stable faces, where new atoms cannot as easily attach themselves.
Ice crystals
Fossil shell with calcite crystals
Vertical cooling crystallizer in a beet sugar factory.
Two types of crystallographic defects. Top right: edge dislocation. Bottom right: screw dislocation.
Twinned pyrite crystal group.
The material holmium–magnesium–zinc (Ho–Mg–Zn) forms quasicrystals, which can take on the macroscopic shape of a pentagonal dodecahedron. Only quasicrystals can take this 5-fold symmetry. The edges are 2 mm long.
Insulin crystals grown in earth orbit.
Hoar frost: A type of ice crystal (picture taken from a distance of about 5 cm).
Gallium, a metal that easily forms large crystals.
An apatite crystal sits front and center on cherry-red rhodochroite rhombs, purple fluorite cubes, quartz and a dusting of brass-yellow pyrite cubes.
Boules of silicon, like this one, are an important type of industrially-produced single crystal.
A specimen consisting of a bornite-coated chalcopyrite crystal nestled in a bed of clear quartz crystals and lustrous pyrite crystals. The bornite-coated crystal is up to 1.5 cm across.
Needle-like millerite crystals partially encased in calcite crystal and oxidized on their surfaces to zaratite; from the Devonian Milwaukee Formation of Wisconsin

Other less exotic methods of crystallization may be used, depending on the physical properties of the substance, including hydrothermal synthesis, sublimation, or simply solvent-based crystallization.

Solubility equilibrium

Type of dynamic equilibrium that exists when a chemical compound in the solid state is in chemical equilibrium with a solution of that compound.

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When a concentrated solution of ammonia is added to a suspension of silver chloride dissolution occurs because a complex of Ag+ is formed

This effect is the basis for the process of recrystallization, which can be used to purify a chemical compound.

List of purification methods in chemistry

Physical separation of a chemical substance of interest from foreign or contaminating substances.

Contamination on agar plate

Recrystallization: In analytical and synthetic chemistry work, purchased reagents of doubtful purity may be recrystallised, e.g. dissolved in a very pure solvent, and then crystallized, and the crystals recovered, in order to improve and/or verify their purity.

Nitric acid

Inorganic compound with the formula HNO3.

Fuming nitric acid contaminated with yellow nitrogen dioxide
Two major resonance representations of HNO3
Nitric acid in a laboratory

These salts can be used to purify gold and other metals beyond 99.9% purity by processes of recrystallization and selective precipitation.

Rhenium

Chemical element with the symbol Re and atomic number 75.

Perrhenic acid (H4Re2O9) adopts an unconventional structure.
Structure of.
Molybdenite
Ammonium perrhenate
The Pratt & Whitney F-100 engine uses rhenium-containing second-generation superalloys
CFM International CFM56 jet engine with blades made with 3% rhenium

Rhenium(VII) oxide and perrhenic acid readily dissolve in water; they are leached from flue dusts and gasses and extracted by precipitating with potassium or ammonium chloride as the perrhenate salts, and purified by recrystallization.

Snow

Snow comprises individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes.

Norwegian train plowing through drifted snow
Extratropical cyclonic snowstorm, February 24, 2007—(Click for animation.)
Frontal snowsquall moving toward Boston, Massachusetts
Cold northwesterly wind over Lake Superior and Lake Michigan creating lake-effect snowfall
Freshly fallen snowflakes
An early classification of snowflakes by Israel Perkins Warren
An animation of seasonal snow changes, based on satellite imagery
New York City during a 2016 blizzard, which
 produced local wind gusts up to 42 mph and dropped 27.5 in of snow, breaking the city's one-day snowfall record.
Snow-covered trees in Kuusamo, Finland
Fresh snow beginning to metamorphose: The surface shows wind packing and sastrugi. In the foreground are hoar frost crystals, formed by refrozen water vapor emerging to the cold surface.
Firn—metamorphosed multi-year snow
Snow drifts forming around downwind obstructions
A powder snow avalanche
Snowmelt-induced flooding of the Red River of the North in 1997
Snow pit on the surface of a glacier, profiling snow properties where the snow becomes increasingly dense with depth as it metamorphoses towards ice
Snowfall and snowmelt are parts of the Earth's water cycle.
Traffic stranded in a 2011 Chicago snowstorm.
Winter conditions on Ontario Highway 401 in Toronto due to a snowsquall.
Deicing an aircraft during a snow event
Satellite view of the Indus River, showing snow in the Himalayas, which feeds it, and agricultural areas in Pakistan that draw on it for irrigation.
Extreme snow accumulation on building roofs
Icings resulting from meltwater at the bottom of the snow pack on the roof, flowing and refreezing at the eave as icicles and from leaking into the wall via an ice dam.
Alpine skiing.
Algae, Chlamydomonas nivalis, that thrive in snow form red areas in the suncups on this snow surface
Arctic fox, a predator of smaller animals that live beneath the snow
Trucks plowing snow on a highway in Missouri
Airport snow-clearing operations include plowing and brushing
Swiss low-profile, train-mounted snowplow
Bivouac of Napoleon's Grande Armée, during the winter retreat from Moscow
Finnish ski troops during the invasion of Finland by the Soviet Union
Army vehicles coping with snow during the Battle of the Bulge of World War II.
Norwegian military preparations during the 2009 Cold Response exercise
Navy SEALs training for winter warfare at Mammoth Mountain, California.

Firn is snow that has persisted for multiple years and has been recrystallized into a substance denser than névé, yet less dense and hard than glacial ice.

Thorium

Weakly radioactive metallic chemical element with the symbol Th and atomic number 90.

The 4n decay chain of 232Th, commonly called the "thorium series"
Thorium dioxide has the fluorite crystal structure. Th4+: __ / O2−: __
Crystal structure of thorium tetrafluoride Th4+: __ / F−: __
Sandwich molecule structure of thorocene
Piano-stool molecule structure of (\h{8}C8H8)ThCl2(THF)2
Estimated abundances of the 83 primordial elements in the Solar system, plotted on a logarithmic scale. Thorium, at atomic number 90, is one of the rarest elements.
The radiogenic heat from the decay of 232Th (violet) is a major contributor to the earth's internal heat budget. Of the four major nuclides providing this heat, 232Th has grown to provide the most heat as the other ones decayed faster than thorium.
Thor's Fight with the Giants (1872) by Mårten Eskil Winge; Thor, the Norse god of thunder, raising his hammer Mjölnir in a battle against the giants.
Jöns Jacob Berzelius, who first identified thorium as a new element
World War II thorium dioxide gas mantle
Glenn T. Seaborg, who settled thorium's location in the f-block
The Indian Point Energy Center (Buchanan, New York, United States), home of the world's first thorium reactor
Yellowed thorium dioxide lens (left), a similar lens partially de-yellowed with ultraviolet radiation (centre), and lens without yellowing (right)
Experiment on the effect of radiation (from an unburned thorium gas mantle) on the germination and growth of timothy-grass seed

During the production of incandescent filaments, recrystallisation of tungsten is significantly lowered by adding small amounts of thorium dioxide to the tungsten sintering powder before drawing the filaments.