Acids and Bases Dr Ron Rusay Spring 2004
Acids and Bases Dr. Ron Rusay Spring 2004 © Copyright 2001 -2004 R. J. Rusay
Introduction to Aqueous Acids & Bases ð Acids: taste sour and cause certain dyes to change color. 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 -2000 R. J. Rusay
Solution Test Apparatus for Electrolytes
Electrolytes Almost all ionic compounds and a few molecular compounds are strong electrolytes. Most molecular compounds 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) 0. 00 mol © Copyright 1995 -2000 R. J. Rusay 0. 10 mol
Strong vs. Weak Electrolytes
Sugar is non-ionized in water and does not conduct.
What is an acid and how strong is it? Acids & Strong Acids: Acids have a proton, H+, eg HCl(aq). A strong acid is 100% ionized. For example nitric acid, HNO 3 , produces 100% H+ (aq). Other common strong acids are sulfuric, H 2 SO 4 (aq) and hydrochloric, HCl (aq) which also produce 100% H+ (aq).
Dissociation of Strong and Weak Acids A weak acid does not dissociate 100%, eg. Acetic acid in vinegar.
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.
Strong or weak acids?
Strong or weak acids?
A scale to relate acidities.
Aqueous Bases Any compound that accepts a proton is a base. The common bases are group IA & IIA 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 -2001 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 has <100% hydroxide ion in aqueous solution. H 3 CNH 2(aq) + H 2 O(l) H 3 CNH 3+(aq) + OH (aq) ð Organic bases are weak bases; for example, dopamine (neurotransmitter), cadaverine (product of cellular decomposition) and morphine (narcotic pain killer) are weak bases.
Strong or weak bases?
Water as an Acid and a Base ðWater is amphoteric (it can behave either as an acid or a base). H 2 O + H 2 O H 3 O+ + OH acid 1 base 1 ð Kw conj acid 2 base 2 = 1 10 14 at 25°C
Water: Self-ionization
The p. H Scale ð p. H log[H+] log[H 3 O+] ð p. H in water ranges from 0 to 14. Kw = 1. 00 10 14 = [H+] [OH ] p. Kw = 14. 00 = p. H + p. OH ð As p. H rises, p. OH falls (sum = 14. 00). There are no theoretical limits on the values of p. H or p. OH. (e. g. p. H of 2. 0 M HCl is -0. 301, the p. H at Iron Mountain is ~ -2 to -3)
The p. H of Some Familiar Aqueous Solutions [H 3 O+] [OH-] = KW [H 3 O+] [OH-] [H 3 O+]> [OH-] [H 3 O+]< [OH-] acidic solution neutral solution basic solution [H 3 O+] = [OH-]
Natural Indicators
The p. H Scale 1 1 x 10 -11 1 x 10 -4 1 x 10 -1 1 3 4 1. 0 12. 0
Neutralization Reactions
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
Acid-Base Titration
Acid-Base Titration
Stomach Chemistry
Buffers
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