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Acids and Bases: Introductory Concepts

Svante Arrhenius. (1859–1927). Acids and Bases: Introductory Concepts. Arrhenius ...acids increase the ______ when dissolved in H 2 O. . [H + ]. [OH – ]. ...bases increase the ______ when dissolved in H 2 O. . e.g., HCl and NaOH . useful concept, but limited to aq. solns. .

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Acids and Bases: Introductory Concepts

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  1. Svante Arrhenius (1859–1927) Acids and Bases: Introductory Concepts Arrhenius ...acids increase the ______ when dissolved in H2O. [H+] [OH–] ...bases increase the ______ when dissolved in H2O. e.g., HCl and NaOH useful concept, but limited to aq. solns. --

  2. : Johannes Bronsted Thomas Lowry (1879–1947) (1874–1936) faster to write; “hydrogen ion” closer to reality; “hydronium ion” 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 are proton acceptors) -- H+ and H3O+ are used interchangeably H+ H3O+ -- B-L concept is NOT limited to aqueous solutions

  3. NH3(aq) + H2O(l) NH4+(aq) + OH–(aq) : (causes [OH–] to ) H–N–H H Arrhenius Bronsted Lowry + [ ] Arrhenius and Bronsted-Lowry definitions overlap, in many cases. B-L base B-L acid (accepts H+) (donates H+) A. base One substance can’t be a Bronsted-Lowry acid unless... another simultaneously acts as a B-L base. -- the acid must be able to lose H+ -- the base must have a nonbonding pair of e– that can bind with the H+ H+ e.g., NH3 in above example

  4. HCl(aq) + H2O(l) B-L base NH3(aq) + H2O(l) B-L acid + – [ [ ] ] Amphoteric substances can be acids or bases, depending on the reaction conditions. H3O+(aq) + Cl–(aq) NH4+(aq) + OH–(aq) NH3 is another example. When a B-L acid, it morphs into NH2– on the P side. “ “ “ base, “ “ “ NH4+ “ “ “ “ .

  5. HNO2(aq) + H2O(l) NO2–(aq) + H3O+(aq) conj. acid base -- 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+. CONJ. BASE ACID

  6. -- Strong acids / bases easily / ____ H+. -- Weak acids / bases do NOT easily / ____ H+. The stronger a/n acid / base, the weaker its conj. base / acid. accept donate accept donate -- In every acid-base rxn, the position of eq. favors the transfer of H+ from stronger acid to stronger base. weaker (conjugate) acid weaker (conjugate) base STRONGER ACID STRONGER BASE

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