Each Na + and OH - ion has a cluster of water molecules surrounding it, with their negative charges closest to the sodium ions and their positive charges closest to the hydroxide ions. These ions interact strongly with the polar water molecules, so NaOH is extremely soluble in water. dissociates into positive and negative ions. Methanol interacts well with water molecules by electrostatic forces. and a small positive charge on the attached hydrogen atom. It has an excess of electrons and a small negative charge on the oxygen atom. It has no local regions of positive and negative charge to attract water molecules, so water is a poor solvent for methane, (c) Methanol, CH 3OH, is polar, although less so than water. (b) The methane molecule, CH 4, is nonpolar: Its electrons are distributed evenly over the molecule. This chapter is concerned with reactions and equilibria in aqueous solution, especially those involving acids and bases.įigure 5-1 Water is a polar molecule, with excess electrons and a partial negative charge on the oxygen atom, and an electron deficiency and a partial positive charge on each hydrogen atom. ![]() Moreover, water molecules dissociate to a small extent into H + and OH - ions, a property that is important in acid-base reactions. Water therefore can interact with other polar molecules. The oxygen atom draws the electrons of the 0 - H bonds toward itself, acquiring a slight negative charge and leaving small positive charges on the two hydrogen atoms. It is polar, in the sense illustrated in Figure 5-1. Solutions of reacting molecules in liquids offer an optimum combination of compactness, ease of handling, and rapidity of mixing of different substances.Īs we saw in Chapter 1, water has special virtues as a solvent. ![]() In contrast, molecules of gases are mobile, but gas volumes are inconveniently large, and many substances cannot be brought into the gas phase without decomposing. Molecules must come into contact to react, and the rates of migration of atoms or molecules within crystals usually are too slow to be useful. There are good reasons for this preference for liquid media. Most of these reactions occur in aqueous solution, where water is the solvent. \)Īlmost all the reactions that a chemist is concerned with take place in solution rather than in gaseous or solid phases.
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