Can Be Separated by Physical Means

Mixtures can also be. separated by taking advantage of a difference in boiling or melting points. Seawater is a mixture of water and a variety of compounds, mostly sodium chloride. Whereas pure water boils at 100°C, sodium chloride doesn t even we/r until 800 C. One way to separate pure water from the mixture we call seawater, therefore, is to heat the seawater to about I00°C. At this temperature, the liquid water readily transforms to water vapor but the sodium chloride stays behind, dissolved in the remaining water. As the water vapor rises, it can be channeled into a cooler container, where it 

Tap water provides us with water as well as a large number of other compouiKls, many of which are flavorful and help us to grow. Bottoms up  

Most of the oxygen in the air bubbles produced by an aquarium aerator escapes into the atmosphere. Some of the oxygen, howes Cr, mixes with the water. It is this orq -gen the fish depend on to survive. Without this dissolved ox) en, which they extract with their gills, the fish would promptly drown. 

So fish don t breathe water. They breathe the oxygen, Oj. dissolved in the water. 

Symbol for sugar molecule, which is sucrose, C,2H220,  

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Mixture A system of two or more substances that can be separated by physical means. 

A is correct. The salts are stereoisomers because they have the same bond-to-bond connectivity, and they must be diastereomers because they can be separated by physical means (crystallization). Notice from the diagram that they are NOT mirror images of each other, and therefore cannot be enantiomers. 

In many cases, amino acids can be resolved by the methods we have already discussed (Section 5-16). If a racemic amino acid is converted to a salt with an optically pure chiral acid or base, two diastereomeric salts are formed. These salts can be separated by physical means such as selective crystallization or chromatography. Pure enantiomers are then regenerated from the separated diastereomeric salts. Strychnine and brucine are naturally occurring optically active bases, and tartaric acid is used as an optically active acid for resolving racemic mixtures. 

Homogeneous mixture (or solution) A system of two or more substances (elements or compounds) that are interspersed, such as the gases making up the air or salt dissolved in water. The individual substances have distinct chemical properties and can be separated by physical means. 

The substances in a mixture can be separated by physical means. For example, if one substance dissolves in a liquid solvent but another does not, the mixture can be filtered. The substance that dissolved will be carried through the filter by the solvent, but the other substance will not. 

There are many different types of mixtures, but they all have these common characteristics They represent physical combinations of two or more substances. The individual substances in a mixture do not lose their original properties, and the substances in a mixture can be separated by physical means. Another characteristic that all mixtures share is that their composition is variable. By this I mean that the substances that are found in the mixture can be mixed in with varying proportions or concentrations. If you mixed in five silver coins and three copper coins, or four silver coins and seven copper coins, you still end up with a mixture of copper and silver coins. 

Figure 1-6 (a) A mixture of iron and sulfur is a heterogeneous mixture, (b) Like any mixture, it can be separated by physical means, such as removing the iron with a magnet. 

Mixtures can be separated by physical means because each component retains its properties (Figures 1-6 and 1-7). For example, a mixture of salt and water can be separated by evaporating the water and leaving the solid salt behind. To separate a mixture of sand and salt, we could treat it with water to dissolve the salt, collect the sand by filtration, and then evaporate the water to reclaim the solid salt. Very fine iron powder can be mixed with powdered sulfur to give what appears to the naked eye to be a homogeneous mixture of the two. Separation of the components of this mixture is easy, however. The iron may be removed by a magnet, or the sulfur may be dissolved in carbon disulfide, which does not dissolve iron (Figure 1-6). 

Unlike compounds, mixtures can be separated by physical means into their components. A heterogeneous mixture has a non-uniform composition with visible boundaries between the components. A homogeneous mixture (solution) has a uniform composition because the components (elements and/or compounds) are mixed as individual atoms, ions, or molecules. 

Recall that mixtures differ fundamentally from compounds in three ways (1) the proportions of the components can vary (2) the individual properties of the components are observable and (3) the components can be separated by physical means. In some cases, as in a mixture of iron and sulfur (Figure 2.19),... 

The mixture still has to be separated and, as it is a mixture of diastereoisomers, it can be separated by physical means. The chloroacetate is just a convenient crystalhne derivative. 

Mixtures are coalitions of more or less uniformly distributed chemical substances that can usually can be separated by physical means. See Terminology, Solutions, p.247. 

The preparation of a material from a nanoobject can be performed by the sol-gel route, by which it is included it as a host compound in a polymerizing mixture of water, solvent and a silica source (TMOS (tetramethoxysilane), TEOS (tetraethoxysilane)) (Fig. 6). The resulting solid is a biphasic system at the molecular scale but also sometimes at the macrometer scale. As a consequence the two components can be separated by physical means. 

One general scheme for separating enantiomers requires chemical conversion of a pair of enantiomers into two diastereomers with the aid of an enantiomerically pure chiral resolving agent. This chemical resolution is successful because the diastereomers thus formed are different compounds, have different physical properties, and often can be separated by physical means (most commonly fractional crystallization or column chromatography) and purified. The final step in this scheme for resolution is chemical conversion of the separated diastereomers back to the individual enantiomers and recovery of the chiral resolving agent. 

Mixtures Most of the materials around us are mixtures. A mixture is a material that can be separated by physical means into two or more substances. Unlike a pure compound, a mixture has variable composition. When you dissolve sodium chloride in water, you obtain a mixture its composition depends on the relative amount of sodium chloride dissolved. You can separate the mixture by the physical process of distillation. ... 

This method involves the chemists following a traditional synthetic route to make the compound, resulting in a racemic mixture. Then they separate the two enantiomers in a process called optical resolution. This involves using a pure enantiomer of another optically active compound (called a chiral auxiliary) that will react with one of the isomers in the mixture. The new product formed will now have different properties and so can be separated by physical means. For example, the solubility in a given solvent will differ so the unwanted enantiomer and the new product can be separated by fractional crystallisation. The new product is then converted back to the desired enantiomer in a simple reaction (e.g. by adding dilute alkali). 

Chemical separation. The mixture is reacted with an optical isomer. The products are then not optical isomers of each other, and can be separated by physical means. For instance, a mixture of D- and L-forms of an acid, acting with a pure L-base, produces two salts that can be separated by fractional crystallization and then reconverted into the acids. 

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