Acids & Bases

Naming Review Binary Acids 1.Start the acid name with “hydro-“ 2.Add the root of the second element with the suffix “ic” 3.Add the word “acid” EX. HCl- hydrochloric acid Polyatomic Acids Use the root name of the polyatomic Add “ic” if the polyatomic ends in –ate What I ATE was ICky Add “ous” if the polyatomic ends in –ite I took a bITE it was deliciOUS Add the word “acid”

Definitions  Acids Ionize to form hydronium ions (H 3 O + ) in water (Arrhenius) Proton donor (Bronsted-Lowry) Electron-pair acceptor (Lewis) HCl + H 2 O  H 3 O + + Cl –

Definitions  Bases Dissociate or ionize to form hydroxide ions (OH - ) in water (Arrhenius) Proton acceptor (Bronsted - Lowry) Electron-pair donor (Lewis) NH 3 + H 2 O  NH OH -

Acid-Base Reactions  Conjugate Base – the species that remains after the acid has given up a proton  Conjugate Acid – the species that is formed when the base gains a proton HCl + H 2 O  H 3 O + + Cl - acid conjugate base conjugate acid base

HF + H 2 O  F - + H 3 O + Acid Base Conjugate Acid Conjugate Base HF H2OH2O H3O+H3O+ F- Acid-Base Reactions

Properties  sour taste  corrosive  electrolytes  turn litmus red  react with metals to form H 2 gas  bitter taste  corrosive  electrolytes  turn litmus blue  slippery feel

Uses  H 3 PO 4 - soft drinks, fertilizer, detergents  H 2 SO 4 - fertilizer, car batteries  HCl - gastric juice  HC 2 H 3 O 2 - vinegar

Uses  NaOH - lye, drain and oven cleaner  Mg(OH) 2 - laxative, antacid  NH 3 - cleaners, fertilizer

Strong vs. Weak  Strong Acid/Base 100% ions in water – completely dissociate strong electrolyte  Weak Acid/Base few ions in water – incomplete dissociation weak electrolyte

Strong Acids  H 2 SO 4 Sulfuric Acid  HClO 4 Perchloric Acid  HClHyrochloric Acid  HNO 3 Nitric Acid  HBrHydrobromic Acid  HIHydroidic Acid

Strong Bases  Ca(OH) 2 Calcium hydroxide  Sr(OH) 2 Strontium hydroxide  Ba(OH) 2 Barium hydroxide  NaOHSodium hydroxide  KOHPotassium hydroxide  RbOHRubidium hydroxide  CsOHCesium hydroxide

pH Scale 0 7 INCREASING ACIDITY NEUTRAL INCREASING BASICITY 14  pH a measure of the concentration of H 3 O + ions in solution measured with a pH meter or an indicator with a wide color range

pH Scale pH of Common Substances

 Which of the following "molecular" pictures best represents a concentrated solution of the weak acid HA? ConcepTest AB

ACID + BASE  SALT + WATER HCl + NaOH  NaCl + H 2 O Neutralization does not always mean pH = 7. = Neutralization Reaction

KOH + HNO 3  H 2 O + KNO 3 Acid? Base? Salt? HNO 3 KOH KNO 3 Neutralization Reaction

Indicators  Indicator Substance that changes color in an acid or base Acid-base indicators are very weak acids and bases that change color when they: –accept a proton from acid –donate one to a base IndicatorColor of acidColor of base Litmus paperRedBlue PhenolphthaleinColorlessPink GoldenrodYellowRed Bromothymol blueYellowBlue

Titration  The controlled addition and measurement of the amount of a solution of known concentration required to react completely with a measured amount of solution of unknown concentration  Equivalence Point – the point at which two solutions used in a titration are present in chemically equivalent amounts Occurs at a pH that is halfway between the two curves  End Point – the point at which an indicator changes color

Titration Beaker – vinegar + phenolphthalein Buret – sodium hydroxide As soon the liquid in the beaker changes color, stop the dropping. Notice the amount of titrating solution used

Titration Curves

strong acid / strong base weak acid / strong base

H 2 O: Acid or Base?  Amphoteric – a species that can react as either an acid or a base NH 3 + H 2 O  NH OH - HCl + H 2 O  H 3 O + + Cl – acid base acid

Self-Ionization of H 2 O  Two water molecules produce a hydronium ion and a hydroxide ion by transfer of a proton H 2 O + H 2 O H 3 O ⁺ + OH ⁻  At 25 C – the concentrations of H 3 O ⁺ + OH ⁻ in pure water are 1.0x10 -7 M  [ H 3 O ⁺ ] = 1.0x10 -7 M[ OH ⁻ ] = 1.0x10 -7 M  Ionization constant of water is K w K w = [ H 3 O ⁺ ] [ OH ⁻ ] K w = [ H 3 O ⁺ ] [ OH ⁻ ] = (1.0x10 -7 M)(1.0x10 -7 M) = 1.0x M 2

Ionization Problems A 1x10 -4 M solution of HNO 3 has been prepared for a lab experiment. a. Calculate [ H 3 O ⁺ ] b. Calculate [ OH ⁻ ]

pH & Concentration  pH of a solution is the negative of the common logarithm of the hydronium ion concentration pH = -log [ H 3 O ⁺ ]  neutral solution at 25C [ H 3 O ⁺ ] = 1.0x10 -7 M pH = -log (1.0x10 -7 ) = -(-7) = 7  pOH = -log (1.0x10 -7 ) = -(-7) = 7  pH + pOH = 14  K w = [ H 3 O ⁺ ] [ OH ⁻ ] =1.0x M 2 -log(1.0x10-14) = 14

pH & Conc. Calculations 1. What is the pH of a 1x10 -3 M NaOH solution? 2. What is the pH of a solution if the [ H 3 O ⁺ ] is 3.4x10 -5 M? 3. Determine the hydronium ion of an aqueous solution that has a pH of 4.0

pH & Conc. Calculations 4. The pH of a solution is measured and determined to be 7.52 a.What is the hydronium ion concentration? b.What is the hydroxide ion concentration? c.Is the solution acidic or basic?