Properties of Acids • Acids taste sour • Acids effect indicators • Blue litmus turns red • Methyl orange turns red • Acids have a pH lower than 7 • Acids are proton (hydrogen ion, H+) donors • Acids react with active metals, produce H2 • Acids react with carbonates • Acids neutralize bases
Acids you must know: Strong Acids Weak Acids Sulfuric acid, H2SO4 Phosphoric acid, H3PO4 Hydrochloric acid, HCl Acetic acid, HC2H3O2 Nitric acid, HNO3
Properties of Bases • Bases taste bitter • Bases effect indicators • Red litmus turns blue • Phenolphthalein turns purple • Bases have a pH greater than 7 • Bases are proton (hydrogen ion, H+) acceptors • Solutions of bases feel slippery • Bases neutralize acids
Examples of Bases • Sodium hydroxide (lye), NaOH • Potassium hydroxide, KOH • Magnesium hydroxide, Mg(OH)2 • Calcium hydroxide (lime), Ca(OH)2
Lewis acids Lewis Acid Bronsted-Lowry Bronsted-Lowry Definitions A Bronsted-Lowry acid is a proton donor; it donates a hydrogen ion, H+. A Bronsted-Lowry base is a proton acceptor; it accepts a hydrogen ion, H+. Lewis Definitions A Lewis acid is a substance than can accept (and share) an electron pair. A Lewis base is a substance than can donate (and share) an electron pair. Acid Definitions Arrhenius acids Arrhenius Acids and Bases Acids release hydrogen ions in water. Bases release hydroxide ions in water. An acid is a substance that produces hydronium ions, H3O+, when dissolved in water.
Acid Definitions Lewis acids The Arrhenius model of acids and bases was broadened by the Bronsted-Lowry model. The Lewis acid-base model is the most general in scope. The Lewis definition of an acid includes any substance that is an electron pair acceptor; a Lewis base is any substance that can act as an electron pair donor. Bronsted-Lowry Arrhenius acids Ralph A. Burns, Fundamentals of Chemistry 1999, page 483
Acids are Proton Donors Monoprotic acids Diprotic acids Triprotic acids H3PO4 HCl H2SO4 HC2H3O2 H2CO3 HNO3
Ionization of HCl and formation of hydronium ion, H3O+ H2O + HCl H3O+ + Cl- Proton acceptor Proton donor
Self-Ionization of Water H2O + H2O H3O+ + OH- Though pure water is considered a non-conductor, there is a slight, but measurable conductivity due to “self-ionization”
Kw – Ionization Constant for Water In pure water at 25 C: [H3O+] = 1 x 10-7 mol/L [OH-] = 1 x 10-7 mol/L Kw is a constant at 25 C: Kw = [H3O+][OH-] Kw = (1 x 10-7)(1 x 10-7) = 1 x 10-14
pH scale : measures acidity/basicity ACID BASE 10x 100x 10x 10x 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 NEUTRAL Each step on pH scale represents a factor of 10. pH 5 vs. pH 6(10X more acidic) pH 3 vs. pH 5 (100X different) pH 8 vs. pH 13 (100,000X different)
Calculating pH, pOH pH = -log10(H3O+) pOH = -log10(OH-) Relationship between pH and pOH pH + pOH = 14 Finding [H3O+], [OH-] from pH, pOH [H3O+] = 10-pH [OH-] = 10-pOH
Strong Acids vs. Weak Acids Strong acids are assumed to be 100% ionized in solution (good proton donors). HCl H2SO4 HNO3 Weak acids are usually less than 5% ionized in solution (poor proton donors). H3PO4 HC2H3O2 Organic acids
Acids Effect Indicators Blue litmus paper turns red in contact with an acid.
Effects of Acid Rain on Marble(calcium carbonate) George Washington: BEFORE George Washington: AFTER
Bases Effect Indicators Red litmus paper turns blue in contact with a base. Phenolphthalein turns purple in a base.
Bases Neutralize Acids Milk of Magnesia contains magnesium hydroxide, Mg(OH)2, which neutralizes stomach acid, HCl. 2 HCl + Mg(OH)2 MgCl2 + 2 H2O
Acids Neutralize Bases HCl + NaOH NaCl + H2O Neutralization reactions ALWAYS produce a salt and water.
NaOH(aq) + HCl(aq) NaCl(aq) + H2O(l) Neutralization Neutralization is a chemical reaction between an acid and a base to produce a salt (an ionic compound) and water. base acid salt water Some neutralization reactions: Na2SO4 + 2 HOH H2SO4(aq) + NaOH(aq) 2 sulfuric acid sodium hydroxide sodium sulfate water Ca(C2H3O2)2 + 2 HOH 2 HC2H3O2(aq) + Ca(OH)2(aq) acetic acid calcium hydroxide calcium acetate water
Neutralization ACID+ BASE SALT + WATER HCl + NaOH NaCl + H2O strong strong neutral HC2H3O2 + NaOH NaC2H3O2 + H2O weak strong basic • Salts can be neutral, acidic, or basic. • Neutralization does not mean pH = 7. Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
NaCl(s) + H2O(l) Na1+(aq) + Cl1-(aq) Salts NaCl Salts - Ionic compounds containing a positive ion other than the hydrogen ion and a negative ion other than the hydroxide ion. i.e., a metal and a non-metal