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4-1 CHAPTER 4 THE MAJOR CLASSES OF CHEMICAL REACTIONS 4.1 The distribution of its bonding electrons and the shape of the molecule are both unsymmetrical. 4.2 Ionic and polar covalent compounds are most likely to be soluble in water. Because water is polar, the partial charges in water molecules are able to interact with the charges, either ionic or dipole-induced, in other substances. 4.3 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. 4.4 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. 4.5 a) 2 — This is the only solution containing a divalent cation (Ca 2+ ). b) 3 — This is the only solution containing a divalent anion (SO 4 2– ). c) 1 — This is the only solution where both the cation (NH 4 + ) and the anion (Br ) are univalent. 4.6 The box in ( 2 ) 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 box (2) has twice as many nitrate ions (red circles) as magnesium ions (blue circles). 4.7 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. 4.8 The interaction with water depends on the structure of the molecule. If the interaction is good, the substance will be soluble; otherwise, the substance will not be very soluble. For example, if a covalent molecule contains polar groups, they will interact well with the polar solvent water. A few covalent molecules, such as HCl, produce ions when dissolving in water. 4.9 In general, covalent compounds which produce ions in 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 ). 4.10 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.
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This note was uploaded on 07/30/2011 for the course CHEM 103 taught by Professor Lewis during the Spring '08 term at Wisc Eau Claire.

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