Acids and Bases Special kinds of aqueous solutions “Ionization” “In nature, acids can be found in fruits: citric acid is responsible for the sharp taste of lemons. Vinegar contains acetic acid, and tannic acid from tree bark is used to tan leather. The stronger mineral acids have been prepared since the Middle Ages. One of these, aqua fortis (nitric acid), was used by assayers to separate gold from silver. Car batteries contain sulfuric acid, also strong and corrosive. A base is the opposite of an acid. Bases often feel slippery; bicarbonate of soda and soap are bases, and so is lye, a substance that can burn skin. Bases that dissolve in water are called alkalis. In water, acids produce hydroxide ions. When an acid and a base react together, the hydrogen and hydroxide ions combine and neutralize each other, forming water together and a salt. The strength of acids and bases can be measured on a pH scale.” Eyewitness Science “Chemistry” , Dr. Ann Newmark, DK Publishing, Inc., 1993, pg 42 http://www.unit5.org/chemistry/AcidBase.html

Properties ACIDS BASES electrolytes electrolytes sour taste bitter taste turn litmus red turn litmus blue react with metals to form H2 gas slippery feel vinegar, milk, soda, apples, citrus fruits ammonia, lye, antacid, baking soda ChemASAP

Common Acids Sulfuric Acid H2SO4 Nitric Acid HNO3 Phosphoric Acid H3PO4 Hydrochloric Acid HCl Acetic Acid CH3COOH Carbonic Acid H2CO3 Battery acid Used to make fertilizers and explosives Food flavoring Stomach acid Vinegar Carbonated water

Common Bases Name Formula Common Name Sodium hydroxide NaOH lye or caustic soda Potassium hydroxide KOH caustic potash Magnesium hydroxide Mg(OH)2 milk of magnesia Calcium hydroxide Ca(OH) 2 slaked lime Ammonia water NH3 H2O household ammonia . NH4OH NH41+ + OH1- ammonium hydroxide

HCl + H2O  H3O+ + Cl– – Definitions + Arrhenius - In aqueous solution… Acids form hydronium ions (H3O+) HCl + H2O  H3O+ + Cl– H Cl O – + acid Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

NH3 + H2O  NH4+ + OH- – Definitions + Arrhenius - In aqueous solution… Bases form hydroxide ions (OH-) NH3 + H2O  NH4+ + OH- H N O – + base Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Definitions: Brønsted-Lowry Acid = any substance that donates a proton. Base = any substance that accepts a proton. 1+ 1- d+ d- + H2O H3O+ Cl- HCl (acid) (base) hydronium ion chloride ion

Definitions: Brønsted-Lowry 1+ + ammonium ion NH4+ 1- hydroxide ion OH- d- d+ NH3 H2O (base) (acid)

Conjugate Acid-Base Pairs conjugates base acid HCl + H2O H3O+ + Cl- acid base conjugates HCl + H2O H3O+ + Cl- acid base CA CB

Conjugate Acid-Base Pairs conjugates acid base NH3 + H2O NH41+ + OH- base acid conjugates base acid CA CB NH3 + H2O NH41+ + OH-

Acid Strength Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 508

Strength (measured [H+] and [OH-]) Strong Acids/Bases 100% ionized in water strong electrolytes - + HCl HNO3 H2SO4 HBr HI HClO3 HClO4 Group 1 Hydroxides (plus Sr(OH)2, Ba(OH)2, and Ca(OH)2) Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Strength (measured [H+] and [OH-]) Weak Acids/Bases do not ionize completely weak electrolytes - + Examples: HF CH3COOH H3PO4 H2CO3 HCN Example: NH3 Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

` pH scale : measures acid/basic concentration 10x 100x 10x 10x Soren Sorensen (1868 - 1939) 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 6 to pH 5 (10X more acidic) pH 3 to pH 5 (100X less acidic) pH 8 to pH 13 (100,000X less acidic)

pH Scale 7 Acid Base 14 Acidic Neutral Basic [H+] pH 10-14 14 10-13 13 10-14 14 10-13 13 10-12 12 10-11 11 10-10 10 10-9 9 10-8 8 10-7 7 10-6 6 10-5 5 10-4 4 10-3 3 10-2 2 10-1 1 100 0 1 M NaOH Ammonia (household cleaner) Blood Pure water Milk Vinegar Lemon juice Stomach acid 1 M HCl Acidic Neutral Basic Acid Base 7 14 pH Scale “S.P.L. Sorensen (1868-1939) introduced the pH scale to measure the concentration of hydrogen ions in solution. The more hydrogen ions, the stronger the acid. The amount of hydrogen ions in solution can affect the color of certain dyes found in nature. These dyes can be used as indicators to test for acids and alkalis. An indicator such as litmus (obtained from lichen) is red in acid. If base is slowly added, the litmus will turn blue when the acid has been neutralized, at about 6-7 on the pH scale. Other indicators will change color at different pH’s. A combination of indicators is used to make a universal indicator.” - Eyewitness Science “Chemistry” , Dr. Ann Newmark, DK Publishing, Inc., 1993, pg 42 Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 515

pH of Common Substance 14 1 x 10-14 1 x 10-0 0 13 1 x 10-13 1 x 10-1 1 pH [H1+] [OH1-] pOH 14 1 x 10-14 1 x 10-0 0 13 1 x 10-13 1 x 10-1 1 12 1 x 10-12 1 x 10-2 2 11 1 x 10-11 1 x 10-3 3 10 1 x 10-10 1 x 10-4 4 9 1 x 10-9 1 x 10-5 5 8 1 x 10-8 1 x 10-6 6 6 1 x 10-6 1 x 10-8 8 5 1 x 10-5 1 x 10-9 9 4 1 x 10-4 1 x 10-10 10 3 1 x 10-3 1 x 10-11 11 2 1 x 10-2 1 x 10-12 12 1 1 x 10-1 1 x 10-13 13 0 1 x 100 1 x 10-14 14 NaOH, 0.1 M Household bleach Household ammonia Lime water Milk of magnesia Borax Baking soda Egg white, seawater Human blood, tears Milk Saliva Rain Black coffee Banana Tomatoes Wine Cola, vinegar Lemon juice Gastric juice More basic 7 1 x 10-7 1 x 10-7 7 More acidic

[H+] [OH-] = 1 x 10-14 M (ionization constant of water (Kw)) pH = - log [H+] pOH = - log [OH-] Given: pH = 4.6 Determine [H+] pH = - log [H+] choose proper equation 4.6 = - log [H+] substitute pH value in equation - 4.6 = log [H+] multiply both sides by -1 2nd log - 4.6 = log [H+] take antilog of both sides [H+] = 2.51x10-5 M 10x antilog Recall, [H+] = [H3O+] You can check your answer by working backwards. pH = - log [H+] pH = - log [2.51x10-5 M] pH = 4.6

Litmus Paper

Indicators phenolphthalein colorless pink acid base weak strong bromthymol blue yellow blue acid base strong universal indicator R O Y G B I V pH 4 7 12

pH Paper pH 0 1 2 3 4 5 6 pH 7 8 9 10 11 12 13

Acid-Base Neutralization 1+ 1- + + H3O+ OH- H2O H2O Hydronium ion Hydroxide ion Water Water Dorin, Demmin, Gabel, Chemistry The Study of Matter 3rd Edition, page 584

ACID + BASE  SALT + 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

moles H3O+ = moles OH- MV n = MV n 100% Neutralization M: Molarity V: volume n: # of H+ ions in the acid or OH- ions in the base Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Titration Equivalence point (endpoint) Point at which equal amounts of H3O+ and OH- are present. Determined by… indicator color change dramatic change in pH Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Titration 42.5 mL of 1.3M KOH are required to neutralize 50.0 mL of H2SO4. Find the molarity of H2SO4. H3O+ M = ? V = 50.0 mL n = 2 OH- M = 1.3M V = 42.5 mL n = 1 MVn = MVn M(50.0mL)(2) =(1.3M)(42.5mL)(1) M = 0.55M H2SO4 Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Neutralization of Bug Bites Wasp - stings with base Red Ant - bites with acid (neutralize with lemon juice or vinegar) (neutralize with baking soda)

Range and Color Changes of Some Common Acid-Base Indicators pH Scale 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Indicators Methyl orange red 3.1 – 4.4 yellow Methyl red red 4.4 6.2 yellow Bromthymol blue yellow 6.2 7.6 blue Neutral red red 6.8 8.0 yellow From F. Brescia et al., Chemistry: A Modern Introduction, W. B. Saunders Co., 1978. Adapted from R. Bates, Determination of pH, Theory and Practice, John Wiley & Sons, Inc., New York, 1964. Phenolphthalein colorless 8.0 10.0 red colorless beyond 13.0 Bromthymol blue indicator would be used in titrating a strong acid with a strong base. Phenolpthalein indicator would be used in titrating a weak acid with a strong base. Methyl orange indicator would be used in titrating a strong acid with a weak base.