1. Properties and Theories
Acids and Bases
Properties and Theories

2. Acids in Ancient Times
Latin “acidus” (sour) was the original name for vinegar
Hydrochloric acid (aka muriatic acid) was discovered around the year 800 by Islamic alchemist Jabir Ibn Hayyan (Gaber).
Nitric acid was known to the alchemists as aqua fortis
Aqua regia, a mixture of nitric and hydrochloric acids, contributed to the effort of alchemists tried to find the philosopher's stone

3. Bases in Ancient Times
Milk of magnesia—magnesium hydroxide
Used as antacid, laxative
Lye—sodium hydroxide
used in tanning, cloth production, and soapmaking
Potash—crude mixture of potassium carbonate and potassium hydroxide
Used as fertilizer
Lye can be made from fowl droppings, human urine, wood ash, powdered limestone, dilute with rain water
Potash can be made by heating wood or other plant materials to an ash in an iron pot
Limewater—solution of calcium hydroxide
or calcium carbonate
Used as a test for CO2, in calamine lotion,
and as an antacid

4. How do acids behave? Sour taste
Acids turn blue litmus paper red (but have no effect on red litmus paper)

5. Properties of Acids
Acids react with certain metals to release hydrogen gas
Mg + HCl  MgCl2 + H2
Form electrolytes in aqueous solutions
Ionize in solution
support electric currents in water

6. How do bases behave?
Bases turn red litmus paper blue (but have no effect on blue litmus paper)
Bitter taste and
slippery feel
Electrolytes in solution
Turns phenolphthalein pink

7. When acids and bases mix
Neutralization reaction occurs
Acid + base  water + salt
First studied quantitatively by German chemist Jeremias Richter
                                         

8. pH scale Proposed by Danish scientist Søren Sørenson in 1909
                                                                                                                                 
Proposed by Danish scientist Søren Sørenson in 1909
Acids have pH < 7
Bases have pH > 7
Neutral substances have pH = 7

9. Operational Definitions
Acids
pH < 7
React with metals to release H2(g)
Sour taste
Turn litmus paper red
Bases
pH > 7
Turn phenolphthalein pink
Turns litmus paper blue
Bitter taste
Slippery feel

10. 1st Acid-Base Theory
Proposed by Swedish chemist Svante Arrhenius in 1887
1903 Nobel Prize in
Chemistry
Studied dissociation of
substances in solution

11. Arrhenius Theory Acids release H+ ions in aqueous solution
Examples of Arrhenius acids
HNO3, HCl, : monoprotic acids
H2SO4 : diprotic acid
H3PO4: triprotic acid
Bases produce OH- ions in aqueous solution
Examples of Arrhenius bases
NaOH, KOH, Mg(OH)2

12. What about ammonia? NH3 Turns litmus paper blue Neutralizes acid
Behaves as a base
Arrhenius theory doesn’t explain it well

13. Brønsted-Lowry Theory
Both independently proposed this theory in 1923
Refined definition of bases
Acid definition very similar to Arrhenius’
All Arrhenius acids are also B-L acids
Johannes Brønsted—Danish chemist
Thomas Lowry—English chemist

14. Brønsted-Lowry Theory
Acids are H+ ion donors or “proton donors”
Bases are H+ acceptors or “proton acceptors”

15. Conjugate Acid-Base Pairs
Acids and bases occur in conjunction
Conjugate acid-base pairs
Differ only by a proton

16. Amphiprotic Substances
Some substances can act as an acid and as a base
Also called “amphoteric”

17. Gilbert Lewis Massachusetts native and MIT chemistry professor
Lewis structures
Lewis acid-base theory an extension of his theory of electron pairs

18. Lewis Theory Proposed same year as B-L theory
Lewis bases: a substance that can donate a pair of electrons to form a covalent bond
Lewis acids: a substance that can accept a pair of electrons to form a covalent bond