Acids and Bases Introductory Concepts Arrhenius H acids
Acids and Bases: Introductory Concepts Arrhenius +] [H. . . acids increase the ______ when dissolved in H 2 O. [OH–]. . . bases increase the ______ when dissolved in H 2 O. e. g. , HCl and Na. OH -- useful concept, but limited to aq. solns. Svante Arrhenius (1859– 1927)
: Bronsted-Lowry acids: can transfer H+ to other substances (i. e. , they are proton donors) Bronsted-Lowry bases: can accept H+ from other substances (i. e. , they Johannes Bronsted Thomas Lowry are proton acceptors) (1879– 1947) (1874– 1936) -- H+ and H 3 O+ are used interchangeably faster to write; “hydrogen ion” closer to reality; “hydronium ion” H+ H 3 O + -- B-L concept is NOT limited to aqueous solutions
Arrhenius and Bronsted-Lowry definitions overlap, in many cases. NH 3(aq) + H 2 O(l) NH 4+(aq) + OH–(aq) B-L base B-L acid (accepts H+) (donates H+) A. base (causes [OH–] to ) Arrhenius Bronsted Lowry One substance can’t be a Bronsted-Lowry acid unless. . . another simultaneously acts as a B-L base. H+ + H–N–H H [ : -- the acid must be able to lose H+ -- the base must have a nonbonding pair of e– that can bind with the H+ e. g. , NH 3 in above example ]
Amphoteric substances can be acids or bases, depending on the reaction conditions. H 3 O+(aq) + Cl–(aq) HCl(aq) + H 2 O(l) B-L base NH 3(aq) + H 2 O(l) NH 4+(aq) + OH–(aq) B-L acid [ NH 3 is another example. + – ] When a B-L acid, it morphs into NH 2– on the P side. “ “ “ base, “ “ “ NH 4+ “ “.
-- In acid-base equilibria, protons are donated in forward and reverse reactions. -- The two substances in a conjugate acid-base pair differ by a H+. . . and the acid has an extra H+. HNO 2(aq) + H 2 O(l) ACID base NO 2–(aq) + H 3 O+(aq) CONJ. BASE conj. acid
-- Strong acids / bases easily donate/ accept ____ H+. -- Weak acids / bases do NOT easily donate/ accept ____ H+. -- The stronger a/n acid / base, the weaker its conj. base / acid. In every acid-base rxn, the position of eq. favors the transfer of H+ from stronger acid to stronger base. STRONGER ACID BASE weaker (conjugate) acid base
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