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- 2. Svante Arrhenius • Swedish chemist (1859-1927) - Nobel prize winner in chemistry (1903) • one of the first chemists to explain the chemical theory of the behavior of acids and bases • Dr. Hubert Alyea-last graduate student of Arrhenius.
- 3. Hubert N. Alyea (1903-1996)
- 4. 1. Arrhenius Definition - 1887 • Acids produce hydrogen ions (H1+ ) in aqueous solution. • Bases produce hydroxide ions (OH1- ) when dissolved in water. • Limited to aqueous solutions. • Only one kind of base (hydroxides) • NH3 (ammonia) could not be an Arrhenius base.
- 6. Polyprotic Acids • Some compounds have more than 1 ionizable hydrogen. • HNO3 nitric acid - monoprotic • H2SO4 sulfuric acid - diprotic - 2 H+ • H3PO4 phosphoric acid - triprotic - 3 H+ • Having more than one ionizable hydrogen does not mean stronger!
- 7. Polyprotic Acids • However, not all compounds that have hydrogen are acids • Also, not all the hydrogen in an acid may be released as ions –only those that have very polar bonds are ionizable - this is when the hydrogen is joined to a very electronegative element
- 8. Arrhenius examples... • Consider HCl • What about CH4 (methane)? • CH3COOH (ethanoic acid, also called acetic acid) - it has 4 hydrogens just like methane does…? • Table 20.4 pg 595 for bases
- 9. Organic Acids Organic acids all contain the “carboxyl” group, (-COOH), sometimes several of them. CH3COOH – of the 4 hydrogen, one 1 ionizable The carboxyl group is a poor proton donor, so ALL organic acids are weak acids.
- 10. 2. Brønsted-Lowry - 1923 • Broader definition than Arrhenius • Acid is hydrogen-ion donor (H+ or proton); base is hydrogen-ion acceptor. • Acids and bases always come in pairs. • HCl is an acid. –When it dissolves in water, it gives it’s proton to water. • HCl(g) + H2O(l) H3O+ + Cl- • Water is a base; makes hydronium ion.
- 11. Johannes Bronsted Thomas Lowry (1879-1947) (1874-1936)
- 12. Why Ammonia is a Base • Ammonia can be explained as a base by using Bronsted-Lowry: NH3(aq) + H2O(l) ↔ NH4 1+ (aq) + OH1- (aq) Ammonia is the hydrogen ion acceptor (base), and water is the hydrogen ion donor (acid). This causes the OH1- concentration to be greater than in pure water, and the ammonia solution is basic
- 13. Acids and bases come in pairs • A “conjugate base” is the remainder of the original acid, after it donates it’s hydrogen ion • A “conjugate acid” is the particle formed when the original base gains a hydrogen ion • Indicators are weak acids or bases that have a different color from their original acid and base
- 14. Acids and bases come in pairs • General equation is: • HA(aq) + H2O(l) ↔ H3O+ (aq) + A- (aq) • Acid + Base ↔ Conjugate acid + Conjugate base • NH3 + H2O ↔ NH4 1+ + OH1- base acid c.a. c.b. • HCl + H2O ↔ H3O1+ + Cl1- acid base c.a. c.b. • Amphoteric – a substance that can act as both and acid and base- as water shows
- 15. 3. Lewis Acids and Bases • Gilbert Lewis focused on the donation or acceptance of a pair of electrons during a reaction • Lewis Acid - electron pair acceptor • Lewis Base - electron pair donor • Most general of all 3 definitions; acids don’t even need hydrogen! • Summary: Table 20.6 page 598
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