ACIDS AND BASES

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 H 2  Acids react with carbonates  Acids neutralize bases

Acids you must know: Strong Acids Weak Acids Hydrochloric acid, HCl Nitric acid, HNO 3 Sulfuric acid, H 2 SO 4 Phosphoric acid, H 3 PO 4 Acetic acid, HC 2 H 3 O 2

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

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, H 3 O +, when dissolved in water. 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. Lewis acids Lewis Acid 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 +. Bronsted-Lowry Arrhenius acids Acid Definitions

Lewis acids Bronsted-Lowry Arrhenius 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. Ralph A. Burns, Fundamentals of Chemistry 1999, page 483

Acid – Base Systems TypeAcidBase ArrheniusH + or H 3 O + producer OH - producer Bronsted- Lowry Proton (H + ) donor Proton (H + ) acceptor LewisElectron-pair acceptor Electron-pair donor

Acids are Proton Donors Monoprotic acidsDiprotic acidsTriprotic acids HCl HC2H3O2HC2H3O2 HNO 3 H 2 SO 4 H 2 CO 3 H 3 PO 4

Ionization of HCl and formation of hydronium ion, H 3 O + H 2 O + HCl  H 3 O + + Cl - Proton donor Proton acceptor

Self-Ionization of Water H 2 O + H 2 O  H 3 O + + OH - Though pure water is considered a non-conductor, there is a slight, but measurable conductivity due to “self-ionization”

Ion Concentration in Solutions

K w – Ionization Constant for Water In pure water at 25  C: [H 3 O + ] = 1 x mol/L [OH - ] = 1 x mol/L K w is a constant at 25  C: Kw = [H 3 O + ][OH - ] Kw = (1 x )(1 x ) = 1 x

pH scale ACIDBASE 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) : measures acidity/basicity 10x 100x

H+, OH-, and pH

Calculating pH, pOH pH = -log 10 (H 3 O + ) pOH = -log 10 (OH - ) Relationship between pH and pOH pH + pOH = 14 Finding [H 3 O + ], [OH - ] from pH, pOH [H 3 O + ] = 10 -pH [OH - ] = 10 -pOH

Strong Acids vs. Weak Acids Strong acids are assumed to be 100% ionized in solution (good proton donors). Weak acids are usually less than 5% ionized in solution (poor proton donors). HClH 2 SO 4 HNO 3 H 3 PO 4 HC 2 H 3 O 2 Organic acids

Strong Acid Dissociation

Weak Acid Dissociation

Acids Effect Indicators Blue litmus paper turns red in contact with an acid.

Acids Have a pH less than 7

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 have a pH greater than 7

Bases Neutralize Acids Milk of Magnesia contains magnesium hydroxide, Mg(OH) 2, which neutralizes stomach acid, HCl. 2 HCl + Mg(OH) 2 MgCl H 2 O

Acids Neutralize Bases HCl + NaOH  NaCl + H 2 O Neutralization reactions ALWAYS produce a salt and water.

Neutralization Neutralization Neutralization is a chemical reaction between an acid and a base to produce a salt (an ionic compound) and water. NaOH(aq) + HCl(aq) NaCl(aq) + H 2 O(l) baseacidsaltwater Some neutralization reactions: H 2 SO 4 (aq) + NaOH(aq) Na 2 SO 4 +HOH sulfuric acidsodium hydroxidesodium sulfatewater HC 2 H 3 O 2 (aq) + Ca(OH) 2 (aq) Ca(C 2 H 3 O 2 ) 2 +HOH acetic acidcalcium hydroxidecalcium acetatewater

Neutralization ACID + BASE  SALT + WATER HCl + NaOH  NaCl + H 2 O HC 2 H 3 O 2 + NaOH  NaC 2 H 3 O 2 + H 2 O –Salts can be neutral, acidic, or basic. –Neutralization does not mean pH = 7. weak strong neutral basic Courtesy Christy Johannesson

Salts Salts 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 NaCl(s) + H 2 O(l) Na 1+ (aq) + Cl 1- (aq) Formulas and names of common salts SALTFORMULACommon Name sodium chlorideNaCl(table) salt sodium nitrateNaNO 3 Chile saltpeter sodium bicarbonateNaHCO 3 baking soda potassium carbonateK 2 CO 3 potash ammonium chlorideNH 4 Clsal ammoniac NaCl