Chapter 13


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13-1 CHAPTER 13 THE PROPERTIES OF MIXTURES: SOLUTIONS AND COLLOIDS 13.1 A heterogeneous mixture has two or more phases, thus seawater has both dissolved and suspended particles. The composition of the seawater is different in various places where a sample may be obtained. 13.2 When a salt such as NaCl dissolves, ion-dipole forces cause the ions to separate, and many water molecules cluster around each of them in hydration shells. Ion-dipole forces hold the first shell. Additional shells are held by hydrogen bonding to inner shells. 13.3 In CH 3 (CH 2 ) n COOH, as n increases, the hydrophobic (CH) portion of the carboxylic acid increases and the hydrophilic part of the molecule stays the same, with a resulting decrease in water solubility. 13.4 Sodium stearate would be a more effective soap because the hydrocarbon chain in the stearate ion is longer than the chain in the acetate ion. A soap forms suspended particles called micelles with the polar end of the soap interacting with the water solvent molecules and the nonpolar ends forming a nonpolar environment inside the micelle. Oils dissolve in the nonpolar portion of the micelle. Thus, a better solvent for the oils in dirt is a more nonpolar substance. The long hydrocarbon chain in the stearate ion is better at dissolving oils in the micelle than the shorter hydrocarbon chain in the acetate ion. 13.5 Hexane and methanol, as gases, are free from any intermolecular forces and can simply intermix with each other. As liquids, hexane is a non-polar molecule, whereas methanol is a polar molecule. “Like dissolves like.” 13.6 Hydrogen chloride (HCl) gas is actually reacting with the solvent (water) and thus shows a higher solubility than propane (C 3 H 8 ) gas, which does not react, even though HCl has a lower boiling point. 13.7 a ) A more concentrated solution will have more solute dissolved in the solvent. Potassium nitrate, KNO 3 , is an ionic compound and therefore soluble in a polar solvent like water. Potassium nitrate is not soluble in the nonpolar solvent CCl 4 . Because potassium nitrate dissolves to a greater extent in water, KNO 3 in H 2 O will result in the more concentrated solution. 13.8 b ) Stearic acid in CCl 4 . Stearic acid will not dissolve in water. It is non-polar while water is very polar. Stearic acid will dissolve in carbon tetrachloride, as both are non-polar. 13.9 To identify the strongest type of intermolecular force, check the formula of the solute and identify the forces that could occur. Then look at the formula for the solvent and determine if the forces identified for the solute would occur with the solvent. The strongest force is ion-dipole followed by dipole-dipole (including H bonds). Next in strength is ion-induced dipole force and then dipole-induced dipole force. The weakest intermolecular interactions are dispersion forces.
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This note was uploaded on 01/18/2009 for the course CHEM 1C taught by Professor Roland during the Spring '08 term at UCSC.

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