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Ch.13 - Properties of Solutions
All textbooksBrown 14th EditionCh.13 - Properties of SolutionsProblem 87
Chapter 13, Problem 87

An “emulsifying agent” is a compound that helps stabilize a hydrophobic colloid in a hydrophilic solvent (or a hydrophilic colloid in a hydrophobic solvent). Which of the following choices is the best emulsifying agent? (a) CH3COOH, (b) CH3CH2CH2COOH, (c) CH3(CH2)11COOH, (d) CH3(CH2)11COONa.

Verified step by step guidance
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Step 1: Understand the role of an emulsifying agent. An emulsifying agent stabilizes a colloid by reducing the surface tension between two immiscible liquids, such as oil and water. It typically has both hydrophilic (water-attracting) and hydrophobic (water-repelling) parts.
Step 2: Analyze the structure of each compound. Look for the presence of both hydrophilic and hydrophobic groups. Carboxylic acids (COOH) and their salts (COONa) are common emulsifying agents due to their polar and non-polar regions.
Step 3: Evaluate each option. (a) CH3COOH is acetic acid, with a short hydrophobic chain and a hydrophilic carboxyl group. (b) CH3CH2CH2COOH is butyric acid, with a slightly longer hydrophobic chain. (c) CH3(CH2)11COOH is lauric acid, with a much longer hydrophobic chain. (d) CH3(CH2)11COONa is sodium laurate, a salt of lauric acid, with a long hydrophobic chain and a hydrophilic ionic group.
Step 4: Consider the effectiveness of each compound as an emulsifying agent. The presence of a charged group, like the sodium ion in option (d), enhances the hydrophilic nature, making it more effective in stabilizing emulsions.
Step 5: Conclude that the best emulsifying agent is likely the one with a balance of hydrophobic and hydrophilic properties, and the presence of an ionic group can significantly enhance emulsification.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Emulsifying Agents

Emulsifying agents are substances that help stabilize emulsions, which are mixtures of two immiscible liquids, such as oil and water. They work by reducing the surface tension between the liquids, allowing for the formation of small droplets that remain suspended. Common examples include surfactants, which have both hydrophilic (water-attracting) and hydrophobic (water-repelling) properties, enabling them to interact with both phases.
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Chelating Agents

Hydrophilic and Hydrophobic Properties

Hydrophilic substances are attracted to water and tend to dissolve or mix well in it, while hydrophobic substances repel water and do not mix well. In the context of emulsifying agents, a good emulsifier typically has a hydrophilic head and a hydrophobic tail, allowing it to interact with both the aqueous and oily phases of an emulsion. This dual nature is crucial for stabilizing emulsions and preventing separation.
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Physical Properties

Colloids and Stability

Colloids are mixtures where tiny particles are dispersed throughout a continuous medium, such as oil droplets in water. The stability of colloids can be affected by factors like particle size, concentration, and the presence of emulsifying agents. A stable colloid will not separate over time, and the choice of emulsifying agent can significantly influence the stability by preventing coalescence of the dispersed phase.
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Suspensions and Colloids
Related Practice
Textbook Question

A dilute aqueous solution of an organic compound soluble in water is formed by dissolving 2.35 g of the compound in water to form 0.250 L of solution. The resulting solution has an osmotic pressure of 0.605 atm at 25 °C. Assuming that the organic compound is a nonelectrolyte, what is its molar mass?

Textbook Question

The osmotic pressure of a 0.010 M aqueous solution of CaCl2 is found to be 0.674 atm at 25 °C. Calculate the van't Hoff factor, i, for the solution.

Textbook Question

Aerosols are important components of the atmosphere. Does the presence of aerosols in the atmosphere increase or decrease the amount of sunlight that arrives at the Earth's surface, compared to an 'aerosol-free' atmosphere? Explain your reasoning.

Textbook Question

The 'free-base' form of cocaine (C17H21NO4) and its protonated hydrochloride form (C17H22ClNO4) are shown below; the free-base form can be converted to the hydrochloride form with one equivalent of HCl. For clarity, not all the carbon and hydrogen atoms are shown; each vertex represents a carbon atom with the appropriate number of hydrogen atoms so that each carbon makes four bonds to other atoms

(a) One of these forms of cocaine is relatively water-soluble: which form, the free base or the hydrochloride?