Crystallization dissolving

If sulphur is present, a black precipitate of ferrous sulphide is obtained when the ferrous sulphate crystals dissolve. Boil the mixture for about 30 seconds, and acidify with dilute sulphuric acid the ferrous sulphide dissolves and a precipitate of Prussian blue forms if nitrogen is present. 

It is often important to control the CSD of pharmaceutical compounds, eg, in the synthesis of human insulin, which is made by recombinant DNA techniques (1). The most favored size distribution is one that is monodisperse, ie, all crystals are of the same size, so that the rate at which the crystals dissolve and are taken up by the body is known and reproducible. Such uniformity can be achieved by screening or otherwise separating the desired size from a broader distribution or by devising a crystallization process that will produce insulin in the desired form. The latter of these options is preferable, and considerable effort has been expended in that regard. 

The optical activity of quartz and certain other materials was first discovered by Jean-Baptiste Biot in 1815 in France, and in 1848 a young chemist in Paris named Louis Pasteur made a related and remarkable discovery. Pasteur noticed that preparations of optically inactive sodium ammonium tartrate contained two visibly different kinds of crystals that were mirror images of each other. Pasteur carefully separated the two types of crystals, dissolved them each in water, and found that each solution was optically active. Even more intriguing, the specific rotations of these two solutions were equal in magnitude and of opposite sign. Because these differences in optical rotation were apparent properties of the dissolved molecules, Pasteur eventually proposed that the molecules themselves were mirror images of each other, just like their respective crystals. Based on this and other related evidence, in 1847 van t Hoff and LeBel proposed the tetrahedral arrangement of valence bonds to carbon. 

Figure 14 reproduces the two curves of Fig. 13, upon which we now make some further comments. The four quantities AF that n up the cycle are indicated in Fig. 14 by the four arrows a, b, c, d. From the form of the diagram it is obvious that, whatever qus ties these four arrows represent, it must be true in every case (c + d) = (a + 6). This must be so for any crystal dissolving in solvent at any temperature. Let us now recall what quantities denoted by the four arrows. Of these a is Lvac, the work require split the crystal at 0°K into its component ions, while b represents free energy of the crystal at room temperature. Neither of these qu< ties depends on the solvent into which the ions are going to be dissol... 

Furthermore, about 1920 the idea had become prevalent that many common crystals, such as rock salt, consisted of positive and negative ions in contact. It then became natural to suppose that, when this crystal dissolves in a liquid, the positive and negative ions go into solution separately. Previously it had been thought that, in each case when the crystal of an electrolyte dissolves in a solvent, neutral molecules first go into solution, and then a certain large fraction of the molecules are dissociated into ions. This equilibrium was expressed by means of a dissociation constant. Nowadays it is taken for granted that nearly all the common salts in aqueous solution are completely dissociated into ions. In those rare cases where a solute is not completely dissociated into ions, an equilibrium is sometimes expressed by means of an association constant that is to say, one may take as the starting point a completely dissociated electrolyte, and use this association constant to express the fact that a certain fraction of the ions are not free. This point of view leads directly to an emphasis on the existence of molecular ions in solution. When, for example, a solution contains Pb++ ions and Cl- ions, association would lead directly to the formation of molecular ions, with the equilibrium... 

Turning next to the unitary part of AS0, this is given in Table 36 under the heading — N(dL/dT). It was pointed out in Secs. 90 and 106 that, to obtain the unitary part of AS0 in aqueous solution, one must subtract 16.0 e.u. for a uni-univalent solute, and 24.0 e.u. for a uni-divalent solute. In methanol solution the corresponding quantities are 14.0 and 21.0 e.u. In Table 36 it will be seen that, except for the first two solutes KBr and KC1, the values are all negative, in both solvents. It will be recalled that for KBr and KC1 the B-coefficients in viscosity are negative, and we associate the positive values for the unitary part of the entropy, shown in Table 29, with the creation of disorder in the ionic co-spheres. In every solvent the dielectric constant decreases with rise of temperature and this leads us to expect that L will increase. For KBr and KC1 in methanol solution, we see from Table 36 that dL/dT has indeed a large positive value. On the other hand, when these crystals dissolve in water, these electrostatic considerations appear to be completely overbalanced by other factors. 

Procedure (copper in crystallised copper sulphate). Weigh out accurately about 3.1 g of copper sulphate crystals, dissolve in water, and make up to 250 mL in a graduated flask. Shake well. Pipette 50 mL of this solution into a small beaker, add an equal volume of ca AM hydrochloric acid. Pass this solution through a silver reductor at the rate of 25 mL min i, and collect the filtrate in a 500 mL conical flask charged with 20 mL 0.5M iron(III) ammonium sulphate solution (prepared by dissolving the appropriate quantity of the analytical grade iron(III) salt in 0.5M sulphuric acid). Wash the reductor column with six 25 mL portions of 2M hydrochloric acid. Add 1 drop of ferroin indicator or 0.5 mL N-phenylanthranilic acid, and titrate with 0.1 M cerium(IV) sulphate solution. The end point is sharp, and the colour imparted by the Cu2+ ions does not interfere with the detection of the equivalence point. 

The crystals dissolve gradually in water and, since dissolution is exothermic due to decomposition of the dichlorophosphoric acid, ice cooling is desirable. 

A crystal is suspended in fresh solvent and 5% of the crystal dissolves in 300 s. How long will it take before 10% of the crystal has dissolved Assume that the solvent can be regarded as infinite in extent, that the mass transfer in the solvent is governed by Fick s second law of diffusion and may be represented as a unidirectional process, and that changes in the surface area of the crystal may be neglected. Start your... 

Emission of li t accompanying the crystallization of certain crystals from solution and probably arising from cleavages occurring during the growth of individual crystals. Thus, it is a form of triboluminescence. Luminescence which appears when crystals dissolve is termed lyoluminescence. 

Some guidelines have been provided for defining the metastable region. If the seed crystals dissolve when added to the metastable solution, this implies that saturation conditions have not been reached. If the addition of the seed leads to the formation of an oil dispersion, it may be concluded that supersaturation has been realized (Anderson, 2000). 

Root intact cells X Solvent for root X Pure substance X Crystals dissolved (0.5 mg)... 

Independent of the growth of ice crystals (Section 1.1.2), which can be observed down to approx. -100 °C, and a possible recrystallization (Section 1.1.3), this chapter describes only such developments or changes of structures that can be influenced by additives. The addition of CPAs to albumins, cells or bacteria influences the nucleation of ice - or at least its growth - in such a way that their natural structures are retained as much as possible. On the other hand, additives are introduced to crystallize dissolve substances. If this method does not help, e. g. with antibiotics, the solution concentrates increasingly until a highly viscous, amorphous substance is included between ice crystals. This condition has disadvantages ... 

The etching of an enantiomorphous pair of asn crystals in the presence of (/ )-aspartic acid and () )-A-methylasparagine is illustrated in Figure 12. Under these conditions, only the R crystals are etched (Figure 12a), whereas the S crystals dissolve smoothly (Figure 12b). The dramatic differences in the surfaces of the two enantiomorphous crystals after dissolution again make it possible to perform a manual Pasteur-type sorting of the R and S crystals with a quantitative enantiomeric yield. 

The selection of the solvent is based on the retention mechanism. The retention of analytes on stationary phase material is based on the physicochemical interactions. The molecular interactions in thin-layer chromatography have been extensively discussed, and are related to the solubility of solutes in the solvent. The solubility is explained as the sum of the London dispersion (van der Waals force for non-polar molecules), repulsion, Coulombic forces (compounds form a complex by ion-ion interaction, e.g. ionic crystals dissolve in solvents with a strong conductivity), dipole-dipole interactions, inductive effects, charge-transfer interactions, covalent bonding, hydrogen bonding, and ion-dipole interactions. The steric effect should be included in the above interactions in liquid chromatographic separation. 

Figure 12 shows the size analyses from one run. Crystal content and solution analysis measurements were In good agreement. The size shown In Figure 12 Is the volume equivalent size, which Is acceptable for crystal growth where the crystals retain the same elongated shape as they grow. However when needle-1Ike crystals dissolve, there Is no longer preferable transfer on particular faces, so the shape changes. If allowance Is not made for this. Incorrect dissolution rates will result. Thus for purposes of...

When phosphine is liquified by pressure in the presence of water, it dissolves partly in the water, the rest floats on the solution. If the pressure is suddenly removed colourless crystals of phosphine hydrate are formed at 2.20 °C under a pressure of 2.8 atm, 11 °C under 6.7 atm, and at 20.0 °C under 151.1 atm. When the pressure is reduced too rapidly the crystals dissolve... 

Black crystaUine solid exists in two modifications stable black needles known as alpha form that produces ruby-red color in transmitted light, and a labile, metastable beta modification consisting of black platelets which appear brownish-red in transmitted light density of alpha form 3.86 g/cm at 0°C density of beta form 3.66 g/cm at 0°C alpha form melts at 27.3°C, vapor pressure being 28 torr at 25°C beta form melts at 13.9°C hquid iodine monochloride has bromine-hke reddish-brown color hquid density 3.10 g/mL at 29°C viscosity 1.21 centipoise at 35°C decomposes around 100°C supercools below its melting point polar solvent as a hquid it dissolves iodine, ammonium chloride and alkali metal chlorides hquid ICl also miscible with carbon tetrachloride, acetic acid and bromine the solid crystals dissolve in ethanol, ether, acetic acid and carbon disulfide solid ICl also dissolves in cone. HCl but decomposes in water or dilute HCl. 

Dosage forms Humalog injection consists of zinc-insulin lispro crystals dissolved... 

Equimolar amounts of 2-acrylamido-2-methyl-l-propanesufonic acid and freshly distilled tris[2-(2-methoxyethoxy)-ethyl]amine were mixed under an inert atmosphere and stirred for 8 hours at ambient temperature or until 2-acrylamido-2-methyl-l-propanesulfonic crystals dissolved. The monomer salt consisted of a slightly yellow viscous clear liquid. The salt monomer was used in the next step without further purification. 

Filter the solution on a funnel for hot filtration and let it stand up to your next lesson. Filter off the formed crystals on a glass filter. Pay attention to the shape of the crystals and compare them with potassium dichromate crystals. Dissolve a small part of the crystals in water and establish what ions are present in the solution. What properties does potassium chlorochromate exhibit What class of chemical compounds does it belong to ... 

Put a small amount of the copper (I) chloride crystals on a watch glass and leave them in the air. What do you observe Introduce a part of the crystals into a test tube containing 2-3 ml of a saturated sodium or potassium chloride solution. When the crystals dissolve, add 1-2 ml of water to the tube. Explain the observed phenomena. Write the equations of the reactions. Retain the remaining salt. 

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