SilberbergChap4ISM

SilberbergChap4ISM - CHAPTER 4 THREE MAJOR CLASSES OF...

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CHAPTER 4 THREE MAJOR CLASSES OF CHEMICAL REACTIONS 4.1 The distribution of its bonding electrons and the shape of the molecule are both unsymmetrical. 4.2 Plan: Review the definition of electrolytes. Solution: Ions must be present in an aqueous solution for it to conduct an electric current. Ions come from ionic compounds or from other electrolytes such as acids and bases. 4.3 The ions on the surface of the solid attract the water molecules (cations attract the “negative” end and anions attract the “positive” end of the water molecules). The interaction of the solvent with the ions overcomes the attraction of the oppositely charged ions for one another, and they are released into the solution. 4.4 a) B — This is the only solution containing a divalent cation (Ca 2+ ). b) C — This is the only solution containing a divalent anion (SO 4 2– ). c) A — This is the only solution where both the cation (NH 4 + ) and the anion (Br ) are univalent. 4.5 Plan: Write the formula for magnesium nitrate and note the ratio of magnesium ions to nitrate ions. Solution: The scene in B best represents a volume of magnesium nitrate solution. Upon dissolving the salt in water, magnesium nitrate, Mg(NO 3 ) 2 , would dissociate to form one Mg 2+ ion for every two NO 3 ions, thus forming twice as many nitrate ions. Only scene B has twice as many nitrate ions (red circles) as magnesium ions (blue circles). 4.6 In some cases, the force of the attraction between the ions is so strong that it cannot be overcome by the interaction of the ions with the water molecules. These materials will be insoluble in water. 4.7 In general, covalent compounds which produce ions in an aqueous solution interact with the water molecules to form either H + ( aq ) or OH ( aq ), producing an acidic or basic (alkaline) solution, respectively. These compounds contain combined hydrogen atoms. Examples include hydrochloric acid (HCl), acetic acid (HC 2 H 3 O 2 ), and ammonia (NH 3 ). 4.8 Plan: Compounds that are soluble in water tend to be ionic compounds or covalent compounds that have polar bonds. Solution: a) Benzene is likely to be insoluble in water because it is non-polar and water is polar. b) Sodium hydroxide, an ionic compound, is likely to be soluble in water since the ions from sodium hydroxide will be held in solution through ion-dipole attractions with water. c) Ethanol (CH 3 CH 2 OH) will likely be soluble in water because the alcohol group ( OH) will hydrogen bond with the water. d) Potassium acetate, an ionic compound, will likely be soluble in water to form sodium ions and acetate ions that are held in solution through ion-dipole attractions to water. 4.9 a) Lithium nitrate, an ionic compound, would be expected to be soluble in water, and the solubility rules confirm this. b) Glycine (H 2 NCH 2 COOH) is a covalent compound, but it contains polar N–H and O–H bonds. This would make the molecule interact well with polar water molecules, and make it likely that it would be soluble .
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This note was uploaded on 04/19/2011 for the course CHM 2046 taught by Professor Veige/martin during the Spring '07 term at University of Florida.

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SilberbergChap4ISM - CHAPTER 4 THREE MAJOR CLASSES OF...

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