Compounds difference from mixtures

The racemic mixture is different still. Though a mixture of enantiomers, J racemates usually act as though they were pure compounds, different from 1 either enantiomer. Thus, the physical properties of racemic tartaric acid differ from those of the two enantiomers and from those of the meso form. 

A favorite demonstration among chemistry teachers, performed to show that the properties of a compound differ from those of its constituent elements, involves iron filings and powdered sulfur. If the teacher takes samples of iron and sulfur and simply mixes them together, the two elements can be separated from each other with a magnet (iron is attracted to a magnet, sulfur is not). If the teacher then combines and heats the mixture of iron and sulfur, a reaction takes place and the elements combine to form iron(ll) sulfide (which is not attracted by a magnet). 

How does the composition of a pure compound differ from that of a mixture ... 

A compound differs from a mixture in that a compound... 

As peroxy compounds differ from one another in solubility, it is obvious that several solvent systems are necessary for their separation. The following solvent systems have been found suitable (49—51) dimethylformamide/ /hexane to benzene ethylene glycol/hexane formamide/hexane -butanol-ethanol-water (45 5 50) or (10 10 1). For detection, sensitive down to 1 pg, the following sprays have been recommended (a) 0.1% p-amino-dimethylaniline hydrochloride and (b) a mixture of 3 ml of glacial acetic acid, 2 ml of a saturated potassium iodide solution, and 5 ml of starch solution. For the chromatography of organic peroxides on thin layers see (52, 53). 

Isoxazole dissolves in approximately six volumes of water at ordinary temperature and gives an azeotropic mixture, b.p. 88.5 °C. From surface tension and density measurements of isoxazole and its methyl derivatives, isoxazoles with an unsubstituted 3-position behave differently from their isomers. The solubility curves in water for the same compounds also show characteristic differences in connection with the presence of a substituent in the 3-position (62HC(17)1, p. 178). These results have been interpreted in terms of an enhanced capacity for intermolecular association with 3-unsubstituted isoxazoles as represented by (9). Cryoscopic measurements in benzene support this hypothesis and establish the following order for the associative capacity of isoxazoles isoxazole, 5-Me, 4-Me, 4,5-(Me)2 3-Me> 3,4-(Me)2 3,5-(Me)2 and 3,4,5-(Me)3 isoxazole are practically devoid of associative capacity. 

The infrared spectrum of 2-hydroxythiophene was originally interpreted as showing both vOH and vC=0 peaks indicating that it exists as a mixture of the hydroxy form 39 (R — H) and at least one of the 0X0 forms, 40 and/or 41. The ultraviolet spectrum of 2-hydroxythiophene is different from that of the corresponding methyl ether (39, R = Me) suggesting the presence of the chromophore contained in structure 40. The facts that this compound gives a positive... 

A compound has a fixed composition, whereas the composition of a mixture may be varied. There are always two H atoms for each O atom in a sample of the compound water, but sugar and sand, for instance, can be mixed in any proportions. Because the components of a mixture are merely mingled with one another, they retain their own chemical properties in the mixture. In contrast, a compound has chemical properties that differ from those of its component elements. The formation of a mixture is a physical change, whereas the formation of a compound requires a chemical change. The differences between mixtures and compounds are summarized in Table G.l. 

Mixtures display the properties of their constituents they differ from compounds, as summarized in Table G.l. Mixtures are classified as homogeneous or heterogeneous, and solutions are homogeneous mixtures. 

The kinetics of thermal decomposition and depolymerisation of various polymers is discussed. The aim of the study was to find reaction conditions where different polymers can be separated from mixtures by decomposing them into their monomers or into pyrolysis products and where chlorine and/or nitrogen are eliminated from the polymers without forming toxic compounds. Data are given for PVC, PS, PE, and PR 13 refs. 

When different portions of a mixture have different compositions, the mixture is said to be heterogeneous. For example, quartz is a pure chemical compound made from silicon and oxygen, and gold is a pure element, but the lump of quartz containing a vein of gold that appears in Figure 1-lla is a heterogeneous mixture because different parts of the lump have different compositions. 

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