Acids and Bases Chapters 20-21

Properties of Acids Sour taste Change the color of dyes known as acid-base indicators (turns litmus red) React with bases to produce a salt (ionic compound) and water Electrolytes (aqueous solutions will conduct electric current) Can react with active metals to give off hydrogen gas (H2)

Definitions of Acids Arrhenius (traditional): compound that contains hydrogen and ionizes in solution to form hydrogen ions (H+) Bronsted-Lowry: molecule or ion that is a proton (H+) donor Lewis: atom or molecule that is an electron-pair acceptor

Number of Protons in Acids Monoprotic acids can donate one H+ ion per molecule Examples: HCl, HNO3, HBr, HClO4 Diprotic acids can donate two H+ ions per molecule Examples: H2SO4, H2Se Triprotic acids can donate three H+ ions per molecule Example: H3PO4 Polyprotic acids can donate more than one H+ ion per molecule H2SO4       H+ + HSO4- HSO4-       H+ + SO42-

Hydronium Ion Hydrogen ion (H+) in an aqueous solution (H2O) becomes H3O+ H3O+ is known as a hydronium ion The terms hydrogen ion (H+), proton (p+), and hydronium ion (H3O+) are used interchangeably

Naming Acids (Review) Binary Acids contain two elements (a cation, H+, and a monatomic anion) hydro______ic acid Oxyacids contains more than two elements (H, O, and 3rd element) (a cation, H+, and a polyatomic anion with O) ________ic acid (-ate ion goes with –ic ending) ________ous acid (-ite ion goes with –ous ending)

Oxyacid Naming Series per______ic acid most oxygen’s ______ic acid goes with –ate anion ______ous acid goes with –ite anion hypo______ous acid least oxygen’s

Properties of Bases Bitter taste Change the color of dyes known as acid-base indicators (turns litmus blue) React with acids to produce a salt (ionic compound) and water Electrolytes (aqueous solutions will conduct electric current) Feel slippery to the skin Basic substances are referred to being “alkaline."

Definitions of Bases Arrhenius (traditional): compound that contains hydroxide and dissociates in solution to form hydroxide ions (OH-) Bronsted-Lowry: molecule or ion that is a proton (H+) acceptor Lewis: atom or molecule that is an electron-pair donor

Naming Bases (Review) Name as ionic compound Cation named first, anion named second Potassium Chloride KCl All transition metals and Pb and Sn need Roman numerals to denote their charge. (Zn, Ag, and Cd don’t need Roman numerals.) Change ending of all nonmetals to –ide to name their monatomic anion. Polyatomic ions must be memorized! Review them if you have forgotten.

Name the Following: H3PO4 Ba(OH)2 HClO2 H3N Al(OH)3 HIO3 H2SO3 HBr Cu(OH)2 H2S phosphoric acid barium hydroxide chlorous acid hydronitric acid aluminum hydroxide iodic acid sulfurous acid hydrobromic acid copper (II) hydroxide hydrosulfuric acid

Neutralization Acid + Base  Ionic Compound + H2O The ionic compound formed from the reaction of an acid and a base is known as a salt. It is formed from the cation of the base and the anion of the acid. The cation from the acid (H+) and the anion from the base (OH-) form the water Hydrolysis: reaction between water and ions of a dissolved salt; causes water to dissociate into H+ and OH- ions

Write balanced equations: barium hydroxide solution mixed with phosphoric acid aqueous sodium hydroxide neutralized with hydrochloric acid aluminum hydroxide solution mixed with chloric acid sulfuric acid reacted with aqueous magnesium hydroxide

Answers: 3 Ba(OH)2 (aq) + 2 H3PO4 (aq)  Ba3(PO4)2 (s) + 6 H2O (l) NaOH (aq) + HCl (aq)  NaCl (aq) + H2O (l) Al(OH)3 (aq) + 3 HClO3 (aq)  Al(ClO3)3 (aq) + 3 H2O (l) H2SO4 (aq) + Mg(OH)2 (aq)  MgSO4 (aq) + 2 H2O (l)

Info for Hydrolysis Worksheet strong acids (ionize 100% in solution): HClO4, HNO3, H2SO4, HI, HBr, HCl strong bases (ionize 100% in solution): Hydroxides of Groups 1 and 2 on Periodic Table If they’re not strong, we assume they are weak!

Bronsted-Lowry Conjugate Acid-Base Pairs Remember, B-L Acid: H+ donor B-L Base: H+ acceptor When an acid is dissolved in water, the acid (HA) donates a proton to water to form a new acid (conjugate acid) and a new base (conjugate base) HA (aq) + H2O (l)  H3O+ (aq) + A- (aq) acid base conjugate acid conjugate base H+ H+

Bronsted-Lowry Acid Conjugate Base HA HCl HNO3 H2SO4 HSO4- H3O+ H2O A- Cl- NO3- HSO4- SO4-2 H2O OH-

A few more items: Amphoteric: any species that reacts as either an acid or a base strong acids have weak conjugate bases weak acids have strong conjugate bases strong acids (ionize 100% in solution): HClO4, HNO3, H2SO4, HI, HBr, HCl strong bases (ionize 100% in solution): Hydroxides of Groups 1 and 2 on Periodic Table

pH notes The pH scale ranges from 0 to 14. Any substance with a pH below 7 is classified as an acid Any substance with a pH above 7 is classified as a base. Substances with a pH of 7 are said to be neutral. (Pure water has a pH of 7.) __________________________________________________________________________ | | | | | | | | | | | | | | | 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 strong acid weak acid neutral weak base strong base

Calculating pH See typed notes

Concentration Comparisons [H+] > [OH-] [H+] < [OH-] [H+] = [OH-] acidic neutral basic

Titration Titration is the method used to determine the concentration of a solution (usually an acid or base). A solution of known concentration (the standard) is added to a measured amount of the solution of unknown concentration until an indicator signals the endpoint. The endpoint occurs when equivalent amounts of H+ and OH- have reacted in a titration, thus neutralizing the resultant solution.

Indicators Acid-base indicators are dyes used in titrations whose colors are sensitive to changes in pH, or hydronium ion concentration. There are many indicators, each indicative of a different pH range. For most titrations, a neutralization reaction is desired. For a strong acid and strong base, the chosen indicator will change near the neutral point at a pH of 7. Examples: phenolphthalein (changes from clear in acid to pink in base) and bromothymol blue (changes from yellow in acid to blue in base)

Sample Titration 50. mL of 0.1 M HCl when titrated with 0.1 M NaOH should take just over 50. mL to cause a color change because it is a monoprotic strong acid being neutralized by a group I hydroxide strong base. (For this titration, we would choose an indicator that changed color at a pH of 7 or neutral to indicate that the acid had been fully neutralized by the added base.) 0.1 M H2SO4 substituted in the above problem would have a different effect since the H+ ion concentration would change for a diprotic acid

Titration Equation MaVa = MbVb nbMaVa = MbVbna In titrations between acids and bases, neutralization is required so the [H+] = [OH-] In order to take this into account, our equation becomes nbMaVa = MbVbna # of H+ ions in base Molarity of acid volume of acid Molarity of base volumeof base # of OH- ions in acid

Functions as an Base or Acid Amphoteric Functions as an Base or Acid