Solutions Colloids and Suspensions

Mixtures of other substances in water can be classified as solutions, colloids, and suspensions.

A solution consists of particles of matter called the solute mixed with a more abundant substance (usually water) called the solvent. The solute can be a gas, solid, or liquid—as in a solution of oxygen, sodium chloride, or alcohol in water, respectively. Solutions are defined by the following properties:

• The solute particles are under 1 nanometer (nm) in size. The solute and solvent therefore cannot be visually distinguished from each other, even with a microscope.

• Such small particles do not scatter light noticeably, so solutions are usually transparent (fig. 2.10a).

• The solute particles will pass through most selectively permeable membranes, such as dialysis tubing and cell membranes.

• The solute does not separate from the solvent when the solution is allowed to stand.

The most common colloid8 in the body is protein, such as the albumin in blood plasma. Many colloids can change from liquid to gel states—gelatin desserts, agar culture media, and the fluids within and between our cells, for example. Colloids are defined by the following physical properties:

• The colloidal particles range from 1 to 100 nm in size.

• Particles this large scatter light, so colloids are usually cloudy (fig. 2.10b).

• The particles are too large to pass through most selectively permeable membranes.

• The particles are still small enough, however, to remain permanently mixed with the solvent when the mixture stands.

8collo = glue + oid = like, resembling

Chapter 2 The Chemistry of Life 65

Chapter 2 The Chemistry of Life 65

Solution Suspension Colloid

Figure 2.10 A Solution, a Colloid, and a Suspension. (a) In this copper sulfate solution, the solute particles are so small that they remain permanently mixed and the solution is transparent. (b) In colloids such as this milk, the particles are still small enough to remain permanently mixed, but they are large enough to scatter light, so we cannot see through the colloid. (c) In suspensions such as this freshly mixed blood, the particles (blood cells) also scatter light and make the mixture opaque. Furthermore, (d) they are too large to remain permanently mixed, so they settle out of the mixture, as in this blood sample that stood overnight.

Figure 2.10 A Solution, a Colloid, and a Suspension. (a) In this copper sulfate solution, the solute particles are so small that they remain permanently mixed and the solution is transparent. (b) In colloids such as this milk, the particles are still small enough to remain permanently mixed, but they are large enough to scatter light, so we cannot see through the colloid. (c) In suspensions such as this freshly mixed blood, the particles (blood cells) also scatter light and make the mixture opaque. Furthermore, (d) they are too large to remain permanently mixed, so they settle out of the mixture, as in this blood sample that stood overnight.

The blood cells in our plasma exemplify a suspension. Suspensions are defined by the following properties:

• The suspended particles exceed 100 nm in size.

• Such large particles render suspensions cloudy or opaque.

• The particles are too large to penetrate selectively permeable membranes.

• The particles are too heavy to remain permanently suspended, so suspensions separate on standing. If allowed to stand, blood cells settle to the bottom of a tube, for example (fig. 2.10c, d).

An emulsion is a suspension of one liquid in another, such as oil and vinegar salad dressing. The fat in breast milk is an emulsion, as are medications such as Kaopectate and milk of magnesia.

A single mixture can fit into more than one of these categories. Blood is a perfect example—it is a solution of sodium chloride, a colloid of protein, and a suspension of

Saladin: Anatomy & I 2. The Chemistry of Life I Text I I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

66 Part One Organization of the Body cells. Milk is a solution of calcium, a colloid of protein, and an emulsion of fat. Table 2.4 summarizes the types of mixtures and provides additional examples.

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Responses

  • selassie
    Is kaopectate an emulsion?
    9 years ago
  • NATALIE
    What are suspensions, colloids and solutions in anatomy?
    8 years ago

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