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Chapter 4 THE ACID-BASE REACTION 4.1 According to the Bronsted-Lowry definition, an acid is a proton donor and a base is a proton acceptor. Compounds that have both a hydrogen and an unshared pair of electrons can potentially react as either an acid or a base, depending on the reaction conditions. For example, water, has both unshared pairs of electrons and hydrogens. Therefore it can act like an acid or a base. a) acid b) both c) acid d) base e) both f) both g) both 4.2 A conjugate acid is formed by adding a proton to the base, using an unshared pair of electrons on the base to form a bond to the proton. The conjugate acid has one unit more of positive charge than the base. For example, addition of a proton to the base hydroxide anion (charge = -1) produces its conjugate acid, H₂O (charge = 0). + a) b) c) CH₃-NH₃ H 4.3 A conjugate base is formed by removing a proton from the acid, leaving the electrons of the bond as an unshared pair on the base. The conjugate base has one unit less of positive charge than the acid. a) b) c) H-N: d) H H 4.4 The reaction of an acid with a base is in equilibrium with the conjugate acid and the conjugate base. Remember, in an acid-base reaction the conjugate acid is the protonated form of the corresponding base and the conjugate base is the deprotonated form of the corresponding acid. 49