Acids and Bases I Dr Ron Rusay Summer
Acids and Bases I Dr. Ron Rusay Summer 2004 © Copyright 2004 R. J. Rusay
Introduction to Aqueous Acids ð Acids: taste sour and cause certain dyes to change color.
Introduction to Aqueous Bases ð Bases: taste bitter, feel soapy and cause certain dyes to turn color.
Electrolytes Aqueous solutions can be categorized into 3 types: non-electrolytes, strong electrolytes or weak electrolytes based on their ability to conduct electricity. A solution must have ions to conduct. Pure Water does not conduct. Aqueous solutions can be tested for conductivity which will determine the degree of ionization of the solutes. It is possible to have full or partial ionization. © Copyright 1995 -2004 R. J. Rusay
Solution Test Apparatus for Electrolytes
Conductivity
Electrolytes / Ionization
Electrolytes Almost all ionic compounds and a few molecular compounds are strong electrolytes. Several molecular compounds are weak conductors, most are non-conductors. Conductivity is directly related to the amount of ionization, i. e. ions in solution. Table salt, sodium chloride, is completely ionized: Na. Cl(s) + H 2 O(l) ---> Na. Cl(aq) ---> 0. 10 mol Na +(aq) + Cl -(aq) © Copyright 1995 -2004 R. J. Rusay
Strong vs. Weak Electrolytes
Models of Acids and Bases ðArrhenius Concept: Acids produce H+ in solution, bases produce OH ion. ðBrønsted-Lowry: Acids are H+ donors, bases are proton acceptors. HCl + H 2 O Cl + H 3 O+
Lewis Acids and Bases ð Lewis Acid: electron pair acceptor ð Lewis Base: electron pair donor
Conjugate Acid/Base Pairs HA(aq) + H 2 O(l) H 3 O+(aq) + A (aq) conj ðconjugate conj base: everything that remains of the acid molecule after a proton is lost. ðconjugate acid: formed when the proton is transferred to the base.
Conjugate Acid/Base Pairs ðconjugate base: everything that remains of the acid molecule after a proton is lost. ðconjugate acid: formed when the proton is transferred to the base.
Acid Strength Strong Acids: 100% of the acid is ionized. For example nitric acid, HNO 3 , produces 100% H+ (aq). Other common strong acids are _______ and ______. Stong acids produce very weak _________, eg. (NO 3 )
Structure and Acid Strength ð Bond polarity & bond strength affects acidity. In binary compounds: Bond Polarity (The higher the bond polarity, the stronger the bond, the weaker the acid) eg. ____ Bond Strength (The lower the bond strength, the higher the resulting H+ ionization and the stronger the acid. ) eg. ____
Dissociation of Strong and Weak Acids
Acid Strength (continued) Weak Acids: A weak acid is not 100% ionized. For example acetic acid, CH 3 COOH, produces <100% H+ (aq). Most acids, particularly organic acids, are weak acids. Weak acids produce a much stronger conjugate base than water, eg. The acetate ion: (CH 3 COO )
Multiprotic Acids ð Monoprotic acids have 1 acidic H, diprotic have 2, eg. Sulfuric acid H 2 SO 4 etc. ð In a strong multiprotic acid, like H 2 SO 4, only the first H is strong; transferring the second H is usually weak H 2 SO 4 + H 2 O H 3 O+1 + HSO 4 -1 + H 2 O H 3 O+1 + SO 4 -2
Aqueous Bases Any compound that accepts a proton is a base. The common bases are _____ metal hydroxide compounds. “Strong” and “weak” are used in the same sense for bases as for acids. ð Strong = complete dissociation (100% hydroxide ion is supplied to the solution) An example of a weak base is ammonia. NH 3 (g) + H 2 O(l) © Copyright 1995 -2004 R. J. Rusay NH 3 (aq) NH 4+(aq)+ OH-(aq)
Bases (continued) ðWeak bases have very little dissociation (or reaction with water), eg. methyl amine like ammonia has <100% hydroxide ion in aqueous solution. ðH 3 CNH 2(aq) + H 2 O(l) H 3 CNH 3+(aq) + ____(aq) ð Organic bases are weak bases; for example, dopamine (neurotransmitter), cadaverine (product of cellular decomposition), morphine (narcotic pain killer) and cocaine are weak bases.
Natural Indicators
Reactions of Acids & Bases • A use for natural indicators: “Neutralization Reactions” • Titrations • Constipation?
Neutralization Reactions How would indicator be used?
Aqueous Reactions: Neutralization Net Ionic Equations HCl(aq) + Na. OH (aq) ---> Na. Cl (aq) + H 2 O(l) __________________________ HCl(aq) ---> H+(aq) + Cl -(aq) ð Na. OH (aq) ---> Na+(aq)+ OH-(aq) ð Na. Cl (aq) ---> Na+(aq)+ Cl-(aq) ð ________________________ Na+(aq)+ OH-(aq) + H+(aq) + Cl -(aq) ---> Na+(aq)+ Cl-(aq) + H 2 O(l) ____________________________ H+(aq) + OH -(aq) ---> H 2 O(l) © Copyright 1995 -2000 R. J. Rusay
Stomach Chemistry
Acid-Base Titration • Acids have p. H < 7, Bases > 7, and 7 is neutral • Without a p. H meter how can the progress of reaction be monitored?
Acid-Base Titration http: //www. dartmouth. edu/~chemlab/techniques/titration. html http: //chemistry. fullerton. edu/~chemdev/director/titrate. html p. H & Water
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