Intersection 10: Acids and Bases. 11/7/06 Reading: 16.1 (p765-770) 16.3-16.7 (p773-794). Exam 1, Problem 12 Regrade. Please turn in your exams by noon on Tuesday, 11/14. A. Outline. Equilibrium wrap up From last week Two everyday examples Practice questions Acids and Bases History
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Reading: 16.1 (p765-770) 16.3-16.7 (p773-794)
Please turn in your exams by noon on Tuesday, 11/14
The only acid know to the ancient Egyptians, Greeks, and Romans was______? It was made by air oxidation of fermented fruit juice (wine)
Among the alkalies known to the ancients were potash (potassium carbonate) obtained from____, soda (sodium carbonate) made by evaporation of alkaline waters, and lime (calcium oxide) made by roasting________. Caustic potash and caustic soda (potassium and sodium hydroxides) were made by the action of lime on soda and potash.
Kauffman, G. B. "The Bronsted-Lowry Acid-Base Concept" J. Chem Ed. 1988, 65, 2831.
Mid-1600's Johann Rudolph Glauber
2 NaCl + H2SO4 2 HCl + Glauber’s salt (Na2SO4)
Acid + base = salt + water
KOH + HNO3 KNO3 + H2O
“Liquor fixus (KOH or K2CO3 solution) and spiritus acidus nitri (HNO3) are in their nature…totally unlike, foes and adversaries of each other…and when the two are brought together…and the one part has overcome and killed the other, neither a fiery liquor nor a spiritus acidus can be found in their dead bodies, but the same has been made, as both were before and from which they were derived namely ordinary saltpeter (KNO3).”
Boyle (1663) noted that acids, in addition to their sour taste, had exceptional solvent power, the ability to color certain blue vegetable dyes red, and a precipitating action on dissolved sulfur.
Alkalies, on the other hand, had a slippery feel and detergent properties, the ability to dissolve oils and sulfur, and the capacity to counteract acids and destroy their properties. Boyle's tests showed that some substances were neutral and did not classify either as acids or alkalies."
Nicholas Lemery (1675) described acids as having sharp spiky atoms, which produced a pricking sensation on the skin, and alkalies as being made up of round particles, which made them feel slippery or soapy.
When acids and bases were mixed, he pictured the sharp needles of the acids as penetrating the porous alkali globules, thus producing salts, which were neither stinging nor slippery to the touch.
Antoine Lavoisier named the gaseous element oxygen in 1777. When sulfur or phosphorus was burned in oxygen, the products dissolved in water to form acids, so he concluded that oxygen was the element common to all acid materials.
Claude Louis Berthollet (1789) showed that prussic acid (HCN) did not contain oxygen
Humphry Davy proved Lavoisier's error more convincingly with muriatic acid (HCl), a very strong acid.
Following the development of the battery by Alessandro Volta (1800), chemists began to use this new device to decompose all kinds of substances. Jons Jacob Berzelius and William Hisinger (1803) found that when salt solutions were subjected to electrolysis, bases were found at the negative pole and acids at the positive pole. They interpreted this to mean that acids and bases must carry opposite electrical charges.
Berzelius concluded that acid-base reactions were simply the result of electrical attractions. His dualistic theory (1812) explained all chemical interactions in terms of neutralization of opposite electrical charges
(PhD describing this work received lowest possible rating from his University)
Svante August Arrhenius, during his study of electro-chemistry, observed that solutions of salts, acids, and bases were the only liquids that would conduct an electric current. He suggested (1884) that when these compounds dissolved in water they dissociated into charged particles, which he called "ions."
According to the Arrhenius theory acids are compounds that produce hydrogen ions in water solution: HCl H+ + Cl- and bases are substances that provide hydroxide ions in water solution: NaOH Na+ + OH-
H3O+ (H2O)6 ref 1
H3O+ (H2O)20 ref 2
Edward Franklin (1905) :
NH4Cl + NaNH2 NaCl + 2 NH3
Thomas Martin Lowry in England and Johannes Nicholas Bronsted in Denmark (1923) independently arrived at a more inclusive definition of the neutralization reaction as the transfer of a hydrogen ion (a proton) from an acid to a base.
If baseballs were really “base”balls….
How do you measure base [OH-]?
Water undergoes an equilibrium process called autoionization.2 H2O(l) → H3O+(aq) + OH-(aq)
An acid that dissociates completely (the equilibrium is shifted all of the way to its conjugate base and hydronium ion) is said to be a strong acid.
HCl(aq) + H2O(l) → H3O+(aq) + Cl-(aq)
acid conj. base
An acid that does not dissociate completely (an equilibrium is established in solution between the acid, its conjugate base, and hydronium ion) is said to be a weak acid.
HClO2(aq) + H2O(l)↔ H3O+(aq) + ClO2-(aq)
acid conj base
Ka = ([H3O+][ClO2-]) / [HClO2]
A base that dissociates completely (the equilibrium is shifted all of the way to its conjugate acid and hydroxide) is said to be a strong base.
NaOH(aq) + H2O(l) → OH-(aq) + Na+(aq)
A base that does not dissociate completely (an equilibrium is established in solution between the base, its conjugate acid, and hydroxide) is said to be a weak base.
(CH3)3N(aq) + H2O(l)↔ (CH3)3NH+(aq) + OH-(aq)
Kb = ([(CH3)3NH+][OH-]) / [(CH3)3N]
There are six strongly dissociating acids:
There are also five bases that dissociate completely in solution (strong):
You should commit the strong acids and bases to memory.
Appendix F in your text book lists Ka and Kb values for many weakly dissociating acids and bases.
H-halogen (HF, HCl, HBr, HI)
H2S (Ka1 = 8.9x10-8)
Oxoacids (H-polyatomic ions) (H2CO3, HNO3, etc.)