Chemistry
Types of Mixtures
Mixtures in chemistry can be classified into two main types: homogeneous and heterogeneous. Homogeneous mixtures have uniform composition and properties throughout, such as saltwater. Heterogeneous mixtures have non-uniform composition and can be visually distinguished, like a salad with different ingredients. These classifications are based on the distribution of the components within the mixture.
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7 Key excerpts on "Types of Mixtures"
eBook - ePub- Barron's Educational Series, Loris Chen(Authors)
- 2020(Publication Date)
- Barrons Educational Services(Publisher)
Chapter 5 Mixtures MixturesMixtures are two or more substances that have been combined in such a way that they retain their individual chemical characteristics. Substances in a mixture can be separated by ordinary mechanical means using physical properties such as magnetism, density, mass, and particle size. Processes such as boiling, evaporation, and condensation can also be used to separate substances in a mixture.Figure 5–1. Homogeneous vs. heterogeneousIf the substances are so well mixed they appear to be a single substance, they are said to be homogeneous. If the substances appear to be separate components, they form a heterogeneous mixture.Solutions are homogeneous mixtures. In solutions the substance that is in the highest concentration is the solvent. The minority substances are solutes. The solvent dissolves the solutes.When a solid or gas substance dissolves, it is said to be soluble. If a solid or gas substance does not dissolve, it is said to be insoluble.If two liquids completely mix into a solution, they are miscible. If two liquids do not mix completely into a solution, they are immiscible.Examples of mixturesSolvent Solute Example Appearance Gas Gas Nitrogen, oxygen, argon, and other gases in dry air Homogeneous Gas Liquid Fog—liquid water in gases of air Homogeneous Gas Solid Microscopic particulate matter mixed in air Homogeneous Liquid Gas Oxygen dissolved in water Homogeneous Liquid Liquid Vinegar and waterOil and water HomogeneousHeterogeneous Liquid Solid Salt mixed in waterPepper mixed in oil HomogeneousHeterogeneous Solid Gas Oxygen trapped in ice Heterogeneous Solid Solid Particles of rocks mixed as sandMetal alloys such as bronze (copper and tin) HeterogeneousHomogeneous Solid Liquid Silver and mercury in dental fillings Homogeneous PAINLESS TIPThe solvent pulls the solute into solution.
- Frederick Bettelheim, William Brown, Mary Campbell, Shawn Farrell(Authors)
- 2019(Publication Date)
- Cengage Learning EMEA(Publisher)
168 Solutions and Colloids 6 CONTENTS 6.1 Introduction to Mixtures 6.2 The Most Common Types of Solutions 6.3 The Distinguishing Characteristics of Solutions 6.4 Factors Affecting Solubility 6.5 The Most Common Units for Concentration 6.6 Water as a Good Solvent 6.7 Colloids 6.8 Colligative Properties 6.1 Introduction to Mixtures In Chapter 2, we discussed pure substances—compounds made of two or more elements in a fixed ratio. Such systems are the easiest to study, so it was convenient to begin with them. In our daily lives, however, we more fre-quently encounter mixtures—systems consisting of more than one compo-nent. Air, smoke, seawater, milk, blood, and rocks, for example, are mixtures (Section 2.2C). Recall that the molecular level is the aspect at which the interactions be-tween molecules becomes significant. If a mixture is uniform throughout at the molecular level, it is called a homogeneous mixture or, more commonly, a solution. Filtered air and seawater, for example, are both solutions. They are clear and transparent. In contrast, in most rocks we can see distinct re-gions separated from each other by well-defined boundaries. Such rocks are heterogeneous mixtures. Another example is a mixture of sand and sugar. We can easily distinguish between the two components; the mixing does not occur at the molecular level (Figure 2.3). Thus, mixtures are classified on the basis of how they look to the unaided eye. Some systems, however, fall between homogeneous and heterogeneous mixtures. Cigarette smoke, milk, and blood plasma may look homogeneous, but they do not have the transparency of air or seawater. These mixtures are classified as suspensions. We will deal with such systems in Section 6.7. Although mixtures can contain many components, we will generally re-strict our discussion to two-component systems, with the understanding that everything we say can be extended to multicomponent systems.
eBook - ePubChemical Thermodynamics
Theory and Applications
- W.J. Rankin(Author)
- 2019(Publication Date)
- CRC Press(Publisher)
When the concentration of one component is very large compared to that of the others, the major component is referred to as the solvent and minor components as solutes. The concentration of the solvent, if required, is usually calculated by subtracting the concentrations of all the solutes from the total concentration (that is, it is calculated by ‘difference’). In some systems, there is a limit to how much solute can dissolve into the solvent. Once this concentration has been reached any further solute component added will remain undissolved and form a separate phase. The solution in this case is said to be saturated with respect to the solute. In other systems, there can be complete miscibility * across the entire composition range. For example, ethanol and water are miscible at all concentrations. In these cases, it is not really necessary, or even possible, to say which component is the solute and which is the solvent. * Miscibility is the property of substances to form a solution. A substance is said to be miscible if it dissolves in a nominated substance or immiscible if it does not. 9.2 Types of solutions Several types of solutions are frequently encountered – gas mixtures, aqueous solutions, organic solutions, molten solutions and solid solutions. Some of these are ionic in nature (many aqueous and molten salt solutions), and others are elemental (solutions consisting only of elements, for example, molten alloys) or molecular in nature (such as many organic solutions) or a combination. We have discussed gas mixtures already in some detail in Chapter 3 and will discuss their thermodynamic properties in Section 9.4. However, we have not yet discussed the other types of solutions, and the following is a brief introduction to their nature as background information. 9.2.1 Aqueous solutions In aqueous solutions the solvent is water. These are the most familiar type of solution
- Mark Kernion, Joseph A. Mascetta, Barron's Educational Series(Authors)
- 2022(Publication Date)
- Barrons Educational Services(Publisher)
alloy.Continuum of Water Mixtures
Figure 7.7 shows the general sizes of the particles found in a water mixture.FIGURE 7.7 Size of Particles in Water MixtureThe basic difference between a colloid and a suspension is the diameter of the particles dispersed. All the boundaries marked in Figure 7.7 indicate only the general ranges in which the distinctions between solutions, colloids, and suspensions are usually made.The characteristics of water mixtures are given in Table 7.7 :TABLE 7.7 The Characteristics of Water MixturesSolutions Colloids Suspensions . . . . . . . . . . . . . . . . . 1 nm . . . . . . . . . . . . . . .1,000 nm . . . . . . . . . . . . . . . . . . . Clear; may have color Particles do not settle. Cloudy; opaque color Settle on standing Particles pass through ordinary filter paper. Do not pass through ordinary filter paper Particles pass through membranes. Do not pass through semipermeable membranes such as animal bladders, cellophane, and parchment, which have very small pores*Particles are not visible. Visible in ultramicroscope Visible with microscope or naked eye Show Brownian movement No Brownian movement * Separation of a solution from a colloidal dispersion through a semipermeable membrane is called dialysis.When a bright light is directed at right angles to the stage of an ultramicroscope, the individual reflections of colloidal particles can be observed to be following a random zigzag path. This is explained as follows: The molecules in the dispersing medium are in motion and continuously bumping into the colloidal particles, causing them to change direction in a random fashion. This motion is called Brownian movement after the Scottish botanist Robert Brown, who first observed it.Solubility
The degree to which a solute can dissolve in a solvent, called solubility, varies with the solute/solvent combination, as seen previously (recall “like dissolves like”). Additionally, temperature influences the solubility of a solute in a solvent. This should make sense, as the production of a solution often involves the solute changing phase and phase change is influenced by temperature, as previously noted. Figure 7.8
eBook - ePub200 Science Investigations for Young Students
Practical Activities for Science 5 - 11
- Martin Wenham(Author)
- 2000(Publication Date)
- SAGE Publications Ltd(Publisher)
MixturesA mixture is made when two or more materials are physically combined or mixed together while remaining chemically distinct. To understand mixtures and their properties it is necessary not only to mix materials and observe the changes this brings about, but also to use and if necessary devise the means of separating them again. Of the nine possible kinds of mixture (all of which exist), children can easily make and investigate four:- solid dispersed in solid: particulate mixtures (Activities 6.4.1 –6.4.3 );
- solid dispersed in liquid: solutions and suspensions (Activities 6.5.1 , 6.5.2 );
- gas dispersed in liquid: solutions (Activity 6.5.3 );
- liquid dispersed in (porous) solid: (Activity 6.6.1 ).
Particulate mixturesThese are made when two or more solids in small particles are mixed. A useful way to investigate and classify such mixtures is to find the means of separating their constituents. It is worth remembering that although the mixtures suggested can all be easily separated, so that in these cases mixing is an easily-reversible change, not all particulate mixtures are of this kind. For example, a mixture of two materials such as finely-ground salt and sugar, both of which are highly soluble in water, is remarkably difficult to separate.Activity 6.4.1
Separating particulate mixtures by particle size
The two most commonly-used methods of separating materials by particle size are sieving and sedimentation. Sieving is more useful for separating larger particles, sedimentation for smaller ones; and while sieving is a good introduction to this kind of separation, sedimentation is more likely to be useful in conjunction with other methods when investigating complex materials, such as soils (see Activity 11.10.2 ).Sieving
eBook - ePubLiquid-State Physical Chemistry
Fundamentals, Modeling, and Applications
- Gijsbertus de With(Author)
- 2013(Publication Date)
- Wiley-VCH(Publisher)
11 Mixing Liquids: Molecular SolutionsSo far, we have discussed pure liquids with increasing complexity. In this chapter we start with solutions and, in particular, with molecular solutions. We first deal briefly with some basic aspects, including molar and partial quantities, perfect, and ideal solutions. Thereafter, nonideal behavior is discussed, based on a treatment of the regular solution model. Finally, some possible improvements are indicated.11.1 Basic Aspects
In this section we iterate and extend somewhat on some of the basic aspects that were introduced in Chapter 2 . The content of a system is defined by the amount of moles nα of chemical species α in the system, often denoted as components, which can be varied independently. A mixture is a system with more than one component. A homogeneous part of a mixture, that is, with uniform properties, is addressed as a phase, while a multicomponent phase is labeled a solution. The majority component of a solution is the solvent, while solute refers to the minority component. We restrict ourselves from the outset to binary mixtures and solutions and use, apart from nα for the number of moles, Nα for the number of molecules and xα for the mole fraction of component α. The label 1 refers always to the solvent (e.g., x1 or 1 − x), while the label 2 indicates the solute (e.g., x2 or x). As usual, NA denotes Avogadro's constant.11.1.1 Partial and Molar Quantities
We refer for an arbitrary extensive quantity Z of a mixture to molar quantities Zm defined by Zm = Z/Σα nα or for single, pure component α by . For solutions, it is also useful to discuss the situation with respect to extensive quantities Z in terms of partial (molar) quantities Zα ≡ (∂Z/∂nα )P,T,n′, where n′ indicates all components except for the component α. Generally, for Z = Z(P,T,nα
eBook - ePubGeneral Physics
Mechanics and Molecular Physics
- L D Landau, A. I. Akhiezer, E.M. Lifshitz(Authors)
- 2013(Publication Date)
- Pergamon(Publisher)
CHAPTER XSOLUTIONS
Publisher Summary
Solutions are mixtures of two or more substances in which the substances are mixed on the molecular scale. The relative amounts of the various substances in the mixture may vary over a more or less wide range. If one substance is present in greater quantity than the others, it is called the solvent and the other substances are called solutes. The composition of a solution is described by its concentration that gives the relation between the quantities of the substances in the mixture —the components of the mixture as they are called. The concentration can be defined in various ways. Physically, the most informative is the molar concentration, that is, the ratio of the numbers of molecules or the ratio of the quantities expressed in moles. Alternatively, one may use concentrations by weight, volume, and so on. The mutual solubility of two substances usually has definite limits; no more than a certain amount of solute can dissolve in a given quantity of solvent. A solution containing the maximum possible quantity of solute is said to be saturated. If further solute is added to such a solution, it will not dissolve. Therefore, it can be said that a saturated solution is one that is in thermal equilibrium with the pure solute. The concentration of the saturated solution is a measure of the ability of a given substance to dissolve in the solvent concerned and is simply called the solubility of the substance. The solubility in general depends on the temperature.§77. Solubility
Solutions are mixtures of two or more substances in which the substances are mixed on the molecular scale. The relative amounts of the various substances in the mixture may vary over a more or less wide range. If one substance is present in greater quantity than the others, it is called the solvent , and the other substances are called solutes
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