2 Key Characteristics of Acids & Bases Taste sourReacts with alkali metals (forms H2 gas)Forms electrolyte solutions (conducts electricity)pH paper color: RedNeutralizes BasesBasesTastes bitterSlippery feelpH paper color: BlueNeutralizes Acids
3 The 3 Main Theories of Acids/Bases Lewis Acids/BasesThis course willmainly deal withBL theoryBronsted-Lowry Acids/BasesArrhenius Acids/Bases
4 Theories of Acids & Bases Arrhenius Theory of Acids & Bases:Properties of acids are due to the presence of H+ ionsExample:HCl H+ + Cl-Properties of bases are due to the presence of OH- ionsNaOH Na OH-
5 HCl(g) + H2O(l) H3O+(aq) + Cl-(aq) What is an H+?H+ ions are bare protonsThese are so reactive that they do not exist naturally, but will bond with water to form a hydronium ion, or H3O+ ionOftentimes H+ and H3O+ are used interchangeablyHCl H+ + Cl-HCl(g) + H2O(l) H3O+(aq) + Cl-(aq)
6 Problems with the Arrhenius theory Only deals with aqueous solutions (solutions in water)Not all acids and bases contain H+ and OH- ionsExample: NH3 is a baseConsidered the most incompletetheory of acids and bases
7 Theories of Acids & Bases Brønsted-Lowry Theory of Acids & BasesAcids are substances that donate H+ ionsAcids are proton (H+) donorsBases are substances that accept H+ ionsBases are proton (H+) acceptorsExample:HBr + H2O H3O Br-A B
8 Brønsted-Lowry Theory The behavior of NH3 can be understood now:NH3 (aq) + H2O (l) ↔ NH4+ (aq) + OH- (aq)NH3 becomes NH4+, so NH3 is a proton acceptor (or a Brønsted-Lowry base)H2O becomes OH-, so H2O is a proton donor (or a Brønsted-Lowry acid)
10 Brønsted-Lowry Theory Conjugate Acid-Base PairsDefinition: An acid and a base that differ only in the presence or absence of H+Every acid has a conjugate base.Every base has a conjugate acid.These pairs only ever differ by exactly one hydrogen ion
11 Brønsted-Lowry Theory Example ProblemsIdentify the Brønsted-Lowry acid, base, conjugate acid and conjugate baseNH3 + H2O NH OH-BACACB
12 Brønsted-Lowry Theory ExampleHCl (g) + H2O (l) ↔ H3O+(aq) + Cl- (aq)HSO HCO3- ↔ SO H2CO3ABCACBABCBCA
13 Theories of Acids & Bases Lewis Acids & BasesAcids are electron acceptorsBases are electron donorsAmphoteric – substances that can act as both an acid and a baseExamples: H2O, HCO3-
14 Summary Of Theories Acids release H+ Bases release OH- ArrheniusAcids release H+Bases release OH-Brønsted-LowryAcids – proton donorBases – proton acceptorLewisAcids – electron acceptorBases – electron donor
15 The pH scaleDeveloped by Søren Sørensen in order to determine the acidity of alesUsed in order to simplify the concept of acids and bases for his workersThe pH scale goes from 0 to 14The acidity/basicity of the solutions depends on the concentration of H+ (or H3O+)
16 The pH scaleAcidicpH < 7NeutralpH = 7BasicpH > 7
17 pH scale Low pH values means a high concentration of H+ (acidic) High pH values means a low concentration of H+ (basic)
18 H2O (l) ↔ H3O+ (aq) + OH- (aq) Calculations of pHThe Self Ionization of WaterIn pure water (pH = 7), the concentrations of the ions (H3O+ and OH-) are equal.[H3O+]=[OH-]= 1x10-7This is because water will spontaneously dissociate naturally:H2O (l) ↔ H3O+ (aq) + OH- (aq)Writing the equilibrium expression for the self-ionization of water gives:
19 The Self-ionization of Water Plugging in the concentrations in pure water, this gives an equilibrium constant of 1x10-14This is referred to as the ion product constant of waterThe ion product constant of water has its own symbol: KwUnlike other equilibrium constants, the Kw will always be the same value
20 Calculations of H3O+/OH- Example #1What is the H3O+ concentration in a solution with [OH-] = 3.0 x 10-4 M?Kw = [H3O+][OH-]1 x = [H3O+][3.0 x 10-4]_________________________3.0 x 10-43.0 x 10-4
21 Calculations of H3O+/OH- If the hydronium-ion concentration of an aqueous solution is 1.0 x 10-3 M, what is the hydroxide ion concentration in the solution? Kw = [H3O+][OH-]1 x = [1 x 10-3][OH-]_________________________1.0 x 10-31.0 x 10-3
22 pH = -log [H3O+] or [H3O+] = 10-pH Calculations of pHpH can be expressed using the following equation:pH = -log [H3O+] or [H3O+] = 10-pHExample #1What is the pH of a solution with M H3O+? Is this solution an acid or a base?Acid!
23 Calculating pH of a solution Example #2What is the pH of a solution where the concentration of hydroxide ions is M? Is this an acid or a base?Kw = [H3O+][OH-] pH = -log [H3O+]Base!
24 Calculating pH of a solution Practice #1Practice #2
25 Calculating H3O+/OH- from pH Example #1What is the hydronium ion concentration in fruit juice that has a pH of 3.3?[H3O+] = 10-pH
26 Calculating H3O+/OH- from pH What are the concentrations of the hydronium and hydroxide ions in a sample of rain that has a pH of 5.05?[H3O+] = 10-pH Kw = [H3O+][OH-]
27 Calculating H3O+/OH- from pH Practice #1Practice #2
28 Strength of Acids & Bases When a solution is considered strong, it will completely ionize in a solutionNitric acid is an example of strong acid:HNO3 (l) + H2O (l) ⇋ NO3- (aq) + H3O+ (aq)In a solution of nitric acid, no HNO3 molecules are present!Strength is NOT equivalent to concentration!
29 Strength of Acids & Bases Knowing the strength of an acid is important for calculating pHIf given concentration of strong acid (such as HNO3) assume it is the same as the concentration of hydronium, H3O+, ionsGiven concentration of a strong base, assume it has the same concentration as the hydroxide, OH-, ions
32 Naming Bases Bases are soluble metal hydroxides Examples Follow identical naming rules for ionic compoundsExamplesNaOHBa(OH)2NH3NH4+Sodium hydroxideBarium hydroxideAmmoniaAmmonium
33 Naming Acids Binary Acids (HX) If the acid has an anion that ends in “-ide” use the following basic format to name the acid:“Hydro – root – ic acid”ExampleHClHydrochloric acid
34 Naming Acids Example Practice HBr HI H2S Hydrobromic acid Hydroiodic acidHydrosulfuric acid
35 Naming Acids Polyatomic acids (aka oxoacids, HxAyOz) Name depends on the polyatomic used:If polyatomic ends in “-ite”, replace with “ous acid”If polyatomic ends in “-ate”, replace with “ic acid”Trick: “I ate something icky”
Your consent to our cookies if you continue to use this website.