Mixtures, 65-66 heterogeneous

In a true solution, which is a homogeneous mixture, the solute particles are less than 1 nm in diameter and remain distributed throughout the solution in a single phase. In contrast, a heterogeneous mixture contains materials that exist in distinct phases. In one 

Solving Problems A Chemistry Handbook Chemistry Matter and Change 157 

Four mixtures having the following properties are examined. Identify each mixture as a solution, a suspension, or a colloid. 

If the properties are not conclusive for identification, state which types of mixtures are possible. 

Define solvation. Explain what happens in terms of attractive forces when a substance dissolves in a solvent. 

As you learned in Chapter 3, most of the forms of matter that you encounter are mixtures. A mixture is a combination of two or more substances that keep their basic identity. Components of a mixture come in contact with each other but do not undergo chemical change. You have been studying homogeneous mixtures called solutions so far in this chapter. Not all mixtures are solutions, however. Heterogeneous mixtures contain substances that exist in distinct phases. Two types of heterogeneous mixtures are suspensions and colloids. 

A suspension is a type of heterogeneous mixture. Suspension particles settle out over time Q, and can be separated from the mixture by filtration 

Category Dispersed particles Dispersing medium Example 

Solid emulsion Liquid Solid Butter, cheese 

Solid foam Gas Solid Marshmallow, soaps that float 

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Separation of the different phases of a heterogeneous mixture should be carried out before homogeneous separation, taking advantage of what already exists. Phase separation tends to be easier and... 

The four principal methods for the separation of heterogeneous mixtures are... 

Let us briefly review the primary treatment methods used. Pretreatment usually starts with phase separation if the effluent is a heterogeneous mixture. 

Benzoylpropionitrile. To a mixture of 21 4 g. of p dimethylamino propiophenone hydrochloride, 13 0 g. of potassium cyanide in a 500 ml. flask, add 260 ml. of boiling water heat the heterogeneous mixture under reflux for 30 minutes. Part of the dimethylamine, which is eliminated in the reaction, distils collect this in dilute hydrochloric acid. Cool the reaction mixture in ice the oil sohdifies and crystals form from the aqueous layer. Collect the solid (crude p benzoylpropiouitrile, 10-5 g.) by suction filtration and recrystallise it from benzene - light petroleum (b.p. 40-60°) it separates as almost colourless blades, m.p. 76°. 

Exothermic oxidation—reduction reactions provide the energy released in both propellant burning and explosive detonation. The reactions are either internal oxidation—reductions, as in the decomposition of nitroglycerin and pentaerythritol tetranitrate, or reactions between discrete oxidizers and fuels in heterogeneous mixtures. 

Fig. 21. A selection of feasible residue curve maps for ternary heterogeneous mixtures where I represents homogeneous and heterogeneous...

In practice, the taffy process is generally employed for only medium molecular-weight resins (1) (n = 1-4). The polymerization reaction results in a highly viscous product (emulsion of water and resin) and the condensation reaction becomes dependent on agitation. At the completion of the reaction, the heterogeneous mixture consists of an alkaline brine solution and a water—resin emulsion and recovery of the product is accompHshed by separation of phases, washing of the taffy resin with water, and removal of water under vacuum. 

The critical properties of water are 374°C (705°F) and 218 atm (3,205 psi). Above this condition a heterogeneous mixture of water, organic-compounds, and oxygen may become homogeneous. Then the rate of oxidation may be considerably accelerated because of (1) elimination of diffusional resistances, (2) increase of oxygen concentration by rea-... 

Heterogeneous Mixtures (Zabetakis, Flammability Characteristics of Combustible Gases and Vapors, Bulletin 627, Bureau of Mines, 1965.) Heterogeneous (poorly mixed) gas phase mixtures can lead to fires that normally would be totally unexpec ted. It is important... 

Heterogeneous mixtures are formed, at least for a short time, when two gases or vapors are first brought together... 

Heterogeneous mixture in which finely divided material is distributed throughout the matrix of another material. Distribution of finely divided solids in a liquid or a solid (e.g., pigments, fillers). 

In order to anticipate problems and to interpret observations under the extreme conditions of shock compression, it is necessary to consider structural and electronic characteristics of PVDF. Although the phenomenological piezoelectric properties of PVDF are similar to those of the piezoelectric crystals, the structure of the materials is far more complex due to its ferroelectric nature and a heterogeneous mixture of crystalline and amorphous phases which are strongly dependent on mechanical and electrical history. 

Horie and his coworkers [90K01] have developed a simplified mathematical model that is useful for study of the heterogeneous nature of powder mixtures. The model considers a heterogeneous mixture of voids, inert species, and reactant species in pressure equilibrium, but not in thermal equilibrium. The concept of the Horie VIR model is shown in Fig. 6.3. As shown in the figure, the temperatures in the inert and reactive species are permitted to be different and heat flow can occur from the reactive (usually hot) species to the inert species. When chemical reaction occurs the inert species acts to ther-... 

Unlike incompatible heterogeneous blends of elastomer-elastomer, elastomer-plastic, and plastic-plastic, the reactively processed heterogeneous blends are expected to develop a variable extent of chemical interaction. For this reason the material properties, interfacial properties, and phase morphology of reactively processed blends would differ significantly from heterogeneous mixtures. 

A heterogeneous mixture of copper sulfate crystals (blue) and saud. 

Two mixtures. On the left is brass, a homogeneous mixture of copper and zinc. On the right is a piece of granite, a heterogeneous mixture that contains discrete regions of different minerals (feldspar, mica, and quartz). 

Nesterovich NI (1979) Equations of turbulent motion of heterogeneous mixtures (in Russian). Prepr of Inst of Theor and Appl Mech USSR Academ of Science, Siberian Branch 8 28... 

The above-described laws of filler distribution in heterogeneous mixtures of polymers are true when the particle size is significantly less than the size of the polymer zones in such mixtures (1 to 10 p). So, powders of graphite and molibdenum (Ss = = 2 m2/g) are distributed equally uniformly in all the studied mixtures of polymers irrespective of the mixing conditions for in this case the particle size is comparable with the size of the polymer zones. 

A heterogeneous mixture of 1.46 mmol of hexanal, 1.96 mmol of allyl bromide, 0.85 mmol of tin powder. 1 mL of Et20, and 1 mL of water is stirred vigorously and 0.1 mL of 5% aq hydrogen bromide is added. After 2 h, the organic layer is separated, washed with NaCl and distilled yield 70%. 

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