Chemistry Chapter Acids and Bases

Acid-Base Theories TheoryAcidBase Arrhenius HC2H3O2HC2H3O2 Produces H + ions in solution HCl Produces OH - ions in solution NaOHCa(OH) 2

Acid-Base Theories TheoryAcidBase Bronsted-Lowry Proton (H + ion) donor. Proton (H + ion) acceptor. Includes more molecules that do not have OH - NH 3 (ammonia) Conjugate Acid-Base Pairs NH 3 + HOH  +OH - NH 4 + Acid (proton donor) Base (conjugate base) proton acceptor Acid (Conjugate acid) proton donor Base (proton acceptor)

Ionization of HCl and formation of hydronium ion, H 3 O + H 2 O + HCl  H 3 O + + Cl - Proton donor Proton acceptor Hydronium ion Chloride ion Acid Conjugate Base Bronsted/Lowry (Acid-Base Pair)

Ionization of HCl and formation of hydronium ion, H 3 O + H 2 O + HCl  H 3 O + + Cl - Proton donor Proton acceptor Hydronium ion Chloride ion Base Conjugate Acid Another Acid-Base Pair

Acids are Proton Donors Monoprotic acidsDiprotic acidsTriprotic acids HCl HC2H3O2HC2H3O2 HNO 3 H 2 SO 4 H 2 CO 3 H 3 PO 4 Note: a proton is a hydrogen ion. “protic” = proton Bronsted/Lowry Theory = proton donor idea (All theories agree these are acids)

Acid-Base Theories TheoryAcidBase Lewis (e- pair) acceptor(e- pair) donor BCl 3 NH 3 N H H H B Cl

Lewis Acid-Base Theory Lewis Acid Lewis Base e- pair acceptore- pair donor Al NH 3 (ammonia) Cl N H H H AlCl 3 (aluminum chloride)

Lewis Acid-Base Theory Lewis Acid Lewis Base e- pair acceptore- pair donor NH 3 (ammonia) Al Cl N H H H AlCl 3 (aluminum chloride)

Amphoteric: A substance that can act as an acid or a base. Water is an example: H 2 O = HOH Acid-Base Theories Summary TheoryAcidBase Arrhenius HC2H3O2HC2H3O2 Produces H + ions in solution HCl Produces OH - ions in solution NaOHCa(OH) 2 Bronsted- Lowry H + ion (proton) donor. H + ion (proton) acceptor. NH 3 (ammonia) Lewis (e- pair) acceptor(e- pair) donor BCl 3 NH 3 HOH

Strong Acid Dissociation H + + H 2 O  H 3 O + Hydronium is a result of proton transfer (H + donated to H 2 O).

Strong Acids Strong acids are assumed to be 100% ionized in solution (good proton donors). HCl H 2 SO 4 HNO 3 H + + Cl - H + + HSO 4 - H + + NO 3 - Arrow in one direction indicates that molecule dissociates completely.

Weak Acids Weak acids are usually less than 5% ionized in solution (poor proton donors). H 3 PO 4 HF H + + F - H + + H 2 PO 4 - H 2 PO 4 - H + + HPO 4 2- Double arrow = (Reaction goes both ways) The larger arrow = (Favored side)

Weak Acid Dissociation Weak acids are mostly molecules. (Only 5% or less dissociate)

Acid Dissociation Constant (Weak Acids) K a = product concentrations vs. reactant concentrations for weak acids. HF (aq) H 3 O + (aq) + F - (aq) H 2 O (l) + K a = [H 3 O + ] [F - ] [HF ] H 2 O not included because it is in a different phase.

Base Dissociation Constant (Weak Bases) K b = product concentrations vs. reactant concentrations for weak acids. NH 3(aq) NH 4 + (aq) + OH - (aq) HOH (l) + K b = [NH 4 + ] [OH - ] [NH 3 ] H 2 O not included because it is in a different phase.

HX (aq) H + (aq) + X - (aq) K a = [H + ] [X - ] [HX ] Initial Change Equilibrium 0.35 M M M 0.35 – = M = (0.041) (0.041) = M

Methyl Red changes from red to orange in this range. Phenolphthalein changes to pink in this range.

HIn (aq) H + (aq) + In - (aq)

Phenolphthalein  Bromthymol blue  Methyl Red (Weakest acid) (Strongest Acid)

H 2 In (aq)  H + (aq) + HIn - (aq) HIn - (aq)  H + (aq) + In 2- (aq) The indicator must be a diprotic acid for 2 color changes. Red to yellow. Yellow to blue.

K w = [H + ] x [OH - ] Ion-product constant = Hydrogen-ion concentration x hydroxide-ion concentration Basic, neutral and acidic are all ways of describing pH concentrations in a solution. The other terms are all associated with bases. The other terms are related to pH or can be calculated from pH.

The other terms are all acid-base theories. Conjugate acids and bases are part of Bronsted-Lowry theory. The other terms describe ionizable hydrogen ions.. Dissociation constants are used with weak acids and bases.

Sulfuric Acid  Highest volume production of any chemical in the U.S.  Used in the production of  Used in the production of paper  Used in production of  Used in production of fertilizers  Used in petroleum refining

Nitric Acid Used in the production of fertilizersUsed in the production of fertilizers Used in the production ofUsed in the production of explosives Nitric acid is a – its reactive components evaporate easilyNitric acid is a volatile acid – its reactive components evaporate easily Stains proteinsStains proteins (including skin!)

Hydrochloric Acid Used in the pickling ofUsed in the pickling of steel Used to purify magnesium from sea waterUsed to purify magnesium from sea water Part of, it aids in the digestion of proteinPart of gastric juice, it aids in the digestion of protein Sold commercially as “Muriatic acid”Sold commercially as “Muriatic acid”

Phosphoric Acid oA flavoring agent in oA flavoring agent in sodas oUsed in the manufacture of detergents oUsed in the manufacture of fertilizers oNot a common reagent oNot a common laboratory reagent

Acetic Acid  Used in the manufacture of  Used in the manufacture of plastics  Used in making pharmaceuticals  Acetic acid is the acid present in  Acetic acid is the acid present in vinegar

Examples of Organic Acids  Citric acid in citrus fruit  Malic acid in sour apples  Deoxyribonucleic acid,  Deoxyribonucleic acid, DNA  Amino acids, the building blocks of protein  Lactic acid in and sore muscles  Lactic acid in sour milk and sore muscles  Butyric acid in rancid butter

Weak Acids: (Organic) HC 2 H 3 O 2 Organic acids (Acids that contain carbon) are always weak acids. H + + C 2 H 3 O 2 - CH 3 COOH H + + CH 3 COO - Carboxylic Acid group: R-COOH Same acid written another way

Organic Acids Organic acids all contain the “carboxyl” group called “carboxylic acid”, sometimes several of them. The carboxyl group is a poor proton donor, so ALL organic acids are weak acids.

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

Products of Neutralization HCl + NaOH  H 2 SO 4 + Ca(OH) 2  HNO 3 + KOH  The products of neutralization are always a ______ and _______. NaCl + H 2 O CaSO H 2 O KNO 3 + H 2 O salt water

Measuring pH with wide-range paper

Narrow-Range pH Paper

pH Indicators and their ranges

Calculating [H + ] and [OH - ] Examples: [H + ] = 1 x pH = 2.0 [H + ] = pH = 12.0 [H + ] = = 5 x pH = 4.3 [OH - ] = 1 x pOH = 4.0 [OH - ] = 1 x pOH = 8.0 [OH - ] = 1 x pOH = 10.0 Acidic Basic Acidic Basic Acidic pH=10 pH=6 pH=4 [H + ] = 10 -pH and [OH - ] = 10 -pOH

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

Acids React with Active Metals Acids react with active metals to form salts and hydrogen gas. Mg + 2HCl  MgCl 2 + H 2 (g)

Acids React with Carbonates 2HC 2 H 3 O 2 + Na 2 CO 3 2 NaC 2 H 3 O 2 + H 2 O + CO 2

Effects of Acid Rain on Marble (calcium carbonate) George Washington: BEFORE George Washington: AFTER

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

Products of Neutralization Products of Neutralization (Lab 23) HCl (aq) + NaOH (aq)  HC 2 H 3 O 2(aq) + NaOH (aq)  HCl (aq) + NH 3 (aq)  NaCl (aq) + H 2 O (l) NaC 2 H 3 O 2 (aq) + H 2 O (l) NH 4 +1 (aq) + Cl -1 (aq) HC 2 H 3 O 2(aq) + NH 3(aq)  NH 4 +1 (aq) + C 2 H 3 O 2 -1 (aq) Trial 1 (Strong acid and Strong Base) Trial 2 (Weak acid and Strong Base) Trial 3 (Strong acid and Weak Base) Trial 4 (Weak acid and Weak Base)

Titration Curves

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

Titration Calculations