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Chapter 13: Problem 86

(a) Many proteins that remain homogeneously distributed in water have molecular masses in the range of 30,000 amu and larger. In what sense is it appropriate to consider such suspensions to be colloids rather than solutions? Explain. (b) What general name is given to a colloidal dispersion of one liquid in another? What is an emulsifying agent?

Short Answer

Expert verified
(a) Protein suspensions in water with molecular masses greater than 30,000 amu are considered colloids because their large size prevents them from dissolving completely and remains homogeneously distributed in water. (b) A colloidal dispersion of one liquid in another is called an emulsion. An emulsifying agent is a substance that stabilizes emulsions by reducing the surface tension between the two immiscible liquids, preventing them from coalescing back into separate phases, such as lecithin in egg yolks or natural gums in salad dressings.

Step by step solution

01

(a) Protein Suspensions: Colloids or Solutions?

Protein suspensions in water usually have molecular masses larger than 30,000 amu. Suspensions can be classified into two categories: colloids and solutions. Solutions are homogeneous mixtures where the solute particles are evenly distributed and are typically very small in size, less than 1 nanometer. Colloids, on the other hand, typically have larger particles with size ranging from 1 nanometer to 1000 nanometers. Since the protein particles in question have molecular masses greater than 30,000 amu and remain homogeneously distributed in water, they would be considered colloids. The large size of these protein particles prevents them from dissolving completely, maintaining a colloidal state.
02

(b) Colloidal Dispersion of One Liquid in Another

A colloidal dispersion in which one liquid is dispersed in another liquid while maintaining separate phases is called an emulsion. Examples of emulsions include milk (fat dispersed in water), mayonnaise (oil dispersed in vinegar), and salad dressing (oil and vinegar).
03

(c) Emulsifying Agents

An emulsifying agent is a substance that is added to stabilize emulsions. Acting as a surface-active agent, they reduce the surface tension between the two immiscible liquids and prevent the droplets from coalescing back into separate phases. Examples of emulsifying agents include lecithin (found in egg yolks and used in making mayonnaise) and natural gums (used in salad dressings).

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Most popular questions from this chapter

Water and glycerol, \(\mathrm{CH}_{2}(\mathrm{OH}) \mathrm{CH}(\mathrm{OH}) \mathrm{CH}_{2} \mathrm{OH},\) are miscible in all proportions. What does this mean? How do the OH groups of the alcohol molecule contribute to this miscibility?

A "canned heat" product used to warm chafing dishes consists of a homogeneous mixture of ethanol \(\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)\) and paraffin that has an average formula of \(\mathrm{C}_{24} \mathrm{H}_{50}\). What mass of \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\) should be added to \(620 \mathrm{~kg}\) of the paraffin in formulating the mixture if the vapor pressure of ethanol at \(35^{\circ} \mathrm{C}\) over the mixture is to be 8 torr? The vapor pressure of pure ethanol at \(35^{\circ} \mathrm{C}\) is 100 torr.

Calculate the molarity of the following aqueous solutions: (a) \(0.540 \mathrm{~g} \mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2}\) in \(250.0 \mathrm{~mL}\) of solution, (b) \(22.4 \mathrm{~g}\) \(\mathrm{LiClO}_{4} \cdot 3 \mathrm{H}_{2} \mathrm{O}\) in \(125 \mathrm{~mL}\) of solution, (c) \(25.0 \mathrm{~mL}\) of \(3.50 \mathrm{M}\) \(\mathrm{HNO}_{3}\) diluted to \(0.250 \mathrm{~L}\)

(a) A sample of hydrogen gas is generated in a closed container by reacting \(2.050 \mathrm{~g}\) of zinc metal with \(15.0 \mathrm{~mL}\) of 1.00 \(M\) sulfuric acid. Write the balanced equation for the reaction, and calculate the number of moles of hydrogen formed, assuming that the reaction is complete. (b) The volume over the solution is \(122 \mathrm{~mL}\). Calculate the partial pressure of the hydrogen gas in this volume at \(25^{\circ} \mathrm{C}\), ignoring any solubility of the gas in the solution. (c) The Henry's law constant for hydrogen in water at \(25^{\circ} \mathrm{C}\) is \(7.8 \times 10^{-4} \mathrm{~mol} / \mathrm{L}\) -atm. Estimate the number of moles of hydrogen gas that remain dissolved in the solution. What fraction of the gas molecules in the system is dissolved in the solution? Was it reasonable to ignore any dissolved hydrogen in part (b)?

At \(35^{\circ} \mathrm{C}\) the vapor pressure of acetone, \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CO},\) is 360 torr, and that of chloroform, \(\mathrm{CHCl}_{3}\), is 300 torr. Acetone and chloroform can form very weak hydrogen bonds between one another as follows: A solution composed of an equal number of moles of acetone and chloroform has a vapor pressure of 250 torr at \(35^{\circ} \mathrm{C}\). (a) What would be the vapor pressure of the solution if it exhibited ideal behavior? (b) Use the existence of hydrogen bonds between acetone and chloroform molecules to explain the deviation from ideal behavior. (c) Based on the behavior of the solution, predict whether the mixing of acetone and chloroform is an exothermic \(\left(\Delta H_{\text {soln }}<0\right)\) or endothermic \(\left(\Delta H_{\text {soln }}>0\right)\) process.
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