October 27, Acids and Bases Chapter 16 Pages
October 27, Arrhenius Definition of Acids & Bases Acids release H + ions when dissolved in water. – HCl(g) H + (aq) + Cl - (aq) Bases release OH - ions when dissolved in water. – NaOH(s) Na + (aq) + OH - (aq)
October 27, HCl(g) H + (aq) + Cl - (aq)
October 27, NaOH(s) Na + (aq) + OH - (aq)
October 27, Limitations of Arrhenius Concept: Restricted to aqueous solutions More general definition offered independently by Johannes Bronsted and Thomas Lowry (1923) Focuses on the transfer of H + ions from one substance to another An H + ion is simply a proton with no surrounding valence electrons; interacts strongly with nonbonding electons pairs of water molecules to form hydronium ions, H 3 O + (aq)
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7 Reaction between HCl and NH 3 (all gases)
October 27, HCl acts as a Bronsted-Lowry Acid; Water is the base.
October 27, Ammonia is a B-L base; Water is the acid.
October 27,
October 27, Bronsted-Lowry Acids & Bases An acid is a substance that can donate a proton to another substance. A base is a substance that can accept a proton. A tug-of-war between an acid & base for proton (in the form of H + ) Because the emphasis is on proton transfer, can be applied to non-aqueous reactions, too.
October 27, A substance can function as an ACID only if another substance simultaneously behaves as a BASE. Acid – must have a H atom to lose as an H + ion Base – must have a nonbonding pair of electrons to bind to H + ion.
October 27, Stupid Sports Analogy… Acids are the quarterback, throwing away a PROTON (football) Bases are the receivers, catching the PROTON, (football)
October 27, Conjugate Acid-Base Pairs Consider a reversible reaction: HX (aq) + H 2 O X - (aq) + H 3 O + (aq)
October 27, When reaction is reversed, X - acts as base and H 3 O + acts as acid. HX (aq) + H 2 O(l) X - (aq) + H 3 O + (aq) Every acid has a conjugate base, formed by removing a proton from the acid. HX (aq) acid X - (aq) conjugate base H 2 O (l) base H 3 O + (aq) conjugate acid
October 27, Conjugate Acid-Base Pairs
October 27, Another Example
October 27, And another,
Conjugate Acid-Base Pairs HBr(aq) + H 2 O (l) If HBr is the acid and H 2 O is the base, write the rest of the reaction….. Br - (aq) + H 3 O + (aq) Br - (aq) is the conj. Base H 3 O + (aq) is the conj. Acid October 27,