3 Ionization of WaterSelf-ionization of water: two water molecules produce a hydronium ion and hydroxide ion by transfer of a protonConcentrations are represented by the molecule’s name enclosed in brackets.Example: [H3O+]Concentrations of hydronium and hydroxyl ions are inversely proportional - as one increases, the other decreases.
4 Ionization Constant Ionization constant of water is Kw It’s equal to the concentration of hydronium ions times hydroxyl ions, which equals 1.0 x[H3O+] x [OH-] = 1.0 x 10-14Ionization of water increases as temperature increases.
5 Solutions Neutral Solution [H3O+] = [OH-] Acidic Solution Basic Solution[H3O+] < [OH-]Calculating Hydronium and Hydroxyl ion concentrationsDo dissociation problem to determine number of moles of specific ion made via one mole of soluteUse strong acids and bases; they completely ionize
7 ExampleA 1.0 x 10-4 M solution of nitric acid has been prepared in a lab. Calculate the hydronium ion concentration and the hydroxyl ion concentration.
8 Solution HNO3 + H2O H30+ + NO3- 1.0 x 10-4 M HNO3 = (1.0 x 10-4 mol / 1 L) x (1 mol H30+ / 1 mol HNO3) = 1.0 x 10-4 M H30+[H3O+] x [OH-] = 1.0 x 10-14[1.0 x 10-4] x [OH-] = 1.0 x 10-14[OH-] = 1.0 x M
9 ExampleBarium Hydroxide has a hydronium ion concentration of 1.0 x What is the hydroxyl concentration? What is the molarity of solution?
10 Solution Ba(OH)2 –> Ba2+ + 2OH- [H3O+] x [OH-] = 1.0 x 10-14 [1.0 x 10-11] x [OH-] = 1.0 x 10-14[OH-] = 1.0 x 10-3 M1.0 x 10-3 M OH = 1.0 x 10-3 mol / 1L1.0 x 10-3 mol OH x (1mol Ba(OH)2 / 2 mol OH) = 5.0 x 10-4 M Ba(OH)2
12 pH Scale pH: negative of the logarithm of hydronium ion concentration pH = -log[H30+]Example:[H30+] = 1x10-7 MpH = -log[1x10-7] = 7pOH: negative logarithm of hydroxide ion concentrationpOH = -log[OH-]
13 pH and pOH Recall that Kw = 1.0 x 10-14 M pH of solutions Therefore, pH + pOH = 14pH of solutionsNeutral: pH = 7.0; pH = pOHBasic: pH > 7.0; pH > pOHAcidic: pH < 7.0; pH < pOH
14 Calculating pHIf starting from hydronium concentration, just take negative logIf starting from hydroxyl concentration, find hydronium concentration, then take negative logCalculate pOH similarlytake negative log for hydroxyl concentrationsfor hydronium concentrations, find hydroxyl concentration and then take negative log
15 Examples What is the pH of a 1.0 x 10-3 M NaOH solution? [OH-] = 1.0 x and [H30+] = 1.0 x 10-11pH = -log(1.0 x 10-11) = 11What is the pOH of a 1.0 x 10-8 M NaOH solution?pOH = -log(1.0 x 10-8) = 8What is the pH of a solution if the [H30+] is 2.7 x 10-3 M?pH = -log(27 x 10-3) = 2.6
17 Calculating Concentrations Find concentrations from pH in reverse orderHydronium concentration = 10-pHExampleDetermine the hydronium concentration of an aqueous solution that has a pH of 4.0[H30+] = 10-pH = 10-4 = 1.0 x 10-4 M
18 Another ExampleA shampoo has a pH of What are the hydronium and hydroxyl ion concentrations?[H30+] = 10-pH = = 2.0 x 10-9 M[H30+][OH-] = 1.0 x 10-14[OH-] = 1.0 x / 2.0 x = 5.0 x 10-6 M
20 IndicatorsAcid-Base Indicator: compounds whose colors are sensitive to pHIndicators change colors because they are either weak acids or weak basesIndicators come in different colors and work over a variety of ranges
22 How Indicators Work Equilibrium indicator eq: HIn <–> H+ + In- An indicator’s colors result from the fact that HIn and In- are different colors.Acidic solutions - In- acts as a base and accepts acid protons. Indicator is then present in largely unionized form, Hin.Basic solutions - H+ ions combine with the base’s OH- ions. The indicator further ionizes since H+ ions have been lost. Indicator is then largely present in the form of In- .
23 Indicators cont’d and pH Meters Transition Interval: pH range over which an indicator changes colorThe lower the pH that an indicator changes colors means the stronger the acid of the indicator.pH Meter: determines pH of solution by measuring the voltage between two electrodes placed in the solution
24 TitrationsDefinition: controlled addition and measurement of amount of solution of known concentration required to react completely with measured amount of solution of unknown concentration
25 More TitrationEquivalence point: point at which two solutions used in titration are present in chemically equivalent amountsEnd point: point in titration where indicator changes colorIf we know the concentration of one solution, we can find the concentration of the other in a titration from the chemically equivalent volumes.
27 Titration SolutionsStandard solution: solution that contains a precisely known concentration of a soluteCompare our known solution concentrations with a solution of a primary standardPrimary standard: highly purified solid compound used to check concentration of known solution in titration
28 Steps to Solve a Titration Problem Start with a balanced equation for neutralization reaction and determine chemically equivalent amounts of acid and baseDetermine moles of acid or base from known solution used during titrationDetermine moles of solute of unknown solution used during titrationDetermine molarity of unknown solution
29 ExampleIn a titration, 27.4 mL of M Ba(OH)2 are added to a 20.0 mL sample of HCl solution of unknown concentration until the equivalence point is reached. What is the molarity of the acid solution?
30 Solution Ba(OH)2 + 2HCl 2H2O + BaCl2 Ba(OH)2 : 27.4 mL, 0.0154 M HCl: 20.0 mL, ?MM = ? Mol Ba(OH)2 / L? = 4.22 x 10-4 mol Ba(OH)24.22 x 10-4 mol Ba(OH)2 x (2HCl / 1 Ba(OH)2) = 8.44 x 10-4 mol HCl8.44 x 10-4 mol HCl / L = M
31 ExampleYou have a vinegar solution you believe to be 0.83 M. You are going to titrate mL of it with a NaOH solution that you know to be M. At what volume of added NaOH solution would you expect to see an end point?
32 Solution HC2H3O2 + NaOH H2O + NaC2H3O2 HC2H3O2: 0.83 M, 0.02000L NaOH: M, ? L0.83 M HC2H3O2 = ? Mol / L? = mol HC2H3O2mol HC2H3O2 x (1 mol NaOH / 1 mol HC2H3O2) = mol NaOH0.519 M NaOH = mol / ? L? = L = 32 mL
33 Created by: Savannah Sisk THE ENDCreated by:Savannah Sisk