Chem 1120 1st Edition Exam 2 Study Guide Lectures 12 25 Lecture 12 February 16 Describe Arrhenius Acids and Bases versus Bronsted Lowry Acids and Bases Arrhenius Acids a substance that directly yields H ions when dissolved in water Arrhenius Bases a substance that directly yields OH ions when dissolved Acid proton donor any species which donates a H Base proton acceptor any species that accepts a H Identify the Bronsted acids and bases in the following equations List the most common strong acids and strong bases have these memorized Most common strong acids HCl HBr HI HClO3 HClO4 HNO3 H2SO4 Most common strong bases LiOH NaOH KOH group 1a metals with hydroxide Ca OH 2 Ba OH 2 Sr OH 2 heavy group 2a metals with hydroxide Remember the important equations when converting pH to pOH etc Kw H OH 1 0 X 10 14 25o pH log10 H pOH log10 OH Lecture 13 February 18 pH pOH 14 Know the differences between strong acids and strong bases Strong acids are by definition strong electrolytes and exist totally ionized in aqueous solutions For monoprotic strong acids H3O acid Strong bases are soluble hydroxides alkali metals and heavier alkali earth metal hydroxides Ca2 Sr2 and Ba2 These also dissociate completely in aqueous solutions For all strong acids Ka is greater than one Ka measures acid strength the weaker the Ka the weaker the acid same for bases with Kb Calculate the concentrations of all the species in 0 2 M H 2SO4 Ka 1 3 X 10 2 and Kb 6 3 X 10 8 Lecture 14 February 23 What are the 2 major types of weak bases Know how to go through with Kb equilibrium calculations same as acids just with Kb values more conversions and about the relationship between Ka and Kb how to do the conversions 2 major categories of weak bases 1 Neutral molecules with lone pairs of electrons ex NH 3 CH3NH2 2 Conjugate bases of weak acids ex HCO 3 FExample Calculate the pH of 0 10 M CH3NH2 Kb 4 4 X 10 4 pKa log Ka pKb log Kb pKa pKb 14 00 Example The pKa of HF is 3 17 What is the value of Kb for the F ion Solution 14 3 17 pKb 10 83 Kb 10 10 83 Kb 1 5 X 10 11 Understand Lewis Base chemistry is the acid or base the electron acceptor Lewis acid electron pair acceptor Lewis base electron pair donor anything that could be a Brondted Lowry base is a Lewis base Example Identify the Lewis acid and Lewis base for each reaction Lecture 15 February 25 What is the common ion effect and how would solve a common ion problem Common Ion Effect the extent of ionization of a weak electrolyte is decreased by adding to the solution a strong electrolyte that has an ion com mon with the weak electrolyte OR a shift in the equilibrium caused by the addition of an ion already present in solution What is the pH of a solution 0 1M in HCN and 0 2M NaCN What is a buffer solution and what equation often proves useful in those types of problems Buffers solutions that resist pH change when small amounts of acid or base are added What is a buffer comprised of weak acid and its conjugate base OR weak base and its conjugate acid Henderson Hasselbalch Equation When 5 mL of HCl is added to a buffer containing 0 1 M NaA and 0 1 M HA pKa 7 what is the resulting pH How do you know what kind of indicator you need for a buffer titration To select the acid base pair for a buffer of a specific pH 1 choose an acid whose pKa is equal to the desired pH and 2 solve the Henderson Hasselbalch equation for the base acid ratio Choose an indicator with a pH near the equivalence point Lecture 16 February 27 Review buffer capacity and titrations what is the equivalence point the endpoint a titration in general Buffer Capacity the amount of acid or base a buffer can neutralize before the pH changes significantly More concentrated buffers have a higher buffer capacity Buffer capacity is highest when the concentrations of weak acid and conjugate base are equal titration the accurate measurement of the volume of solution required to completely react with a sample Equivalence point the point at which stoichiometrically equivalent quantities of reactants are brought together Endpoint the point at which indicator changes color very near to equivalence point What are the four regions types of problems to go along with titrating a strong acid into a strong base 1 before titrant is added single point 2 region up to the equivalence point 2 region up to the equivalence point 3 at the equivalence point single point 4 region after the equivalence point Region 1 Treat as strong acid problem Region 2 Treat as limiting reagent problem Region 3 Treat as complete neutralization Region 4 Treat as limiting reagent problem Lecture 17 March 2 Divide up the curve of weak acid strong base strong base into the weak acid and know how to do calculations for each of the four parts Region 1 before titrant weak acid problem Point 2 before equivalence point buffer problem 5 mL 0 1 M NaOh is added 0 1M X 25 mL 2 5 mmol HAc 0 1 M X 5 mL 0 5 mmol NaOH HAc aq OH aq H2O l Ac aq before change after 2 5mmol 0 5 2mmol 0 5mmol 0mmol 0 5 0 5 0mmol 0 5mmol Use Henderson Hasselbalch Equation base acid 0 5mmol 30mL 2mmol 30mL 0 5 2 0 250 pH 4 745 log 0 25 4 143 Region 3 equivalence point neutralization then weak base problem 0 1M X 25 mL 2 5 mmol NaOH 0 1 X 25 mL 2 5 mmol HAc make ICE table end up with 0 mmol HAc 0 mmol OH 2 5 mmol Ac Ac 2 5mmol 25mL 25mL 0 05 M Ac water HAc OH make another ICE table end up with 0 05 X Ac X HAc X OHplug into the Kb equation Kb Kw Ka you end up getting x OH 5 27 X 10 6 which means the pOH is log 5 27 X 10 6 5 278 pH 14 pOH 8 721 Region 3 equivalence point neutralization then weak base problem 0 1M X 25 mL 2 5 mmol NaOH 0 1 X 25 mL 2 5 mmol HAc make ICE table end up with 0 mmol HAc 0 mmol OH 2 5 mmol Ac Ac 2 5mmol 25mL 25mL 0 05 M Ac water HAc OH make another ICE table end up with 0 05 X Ac X HAc X OHplug into the Kb equation Kb Kw Ka you end up getting x OH 5 27 X 10 6 which means the pOH is log 5 27 X 10 6 5 278 pH 14 pOH 8 721 Region 4 after equivalence point limiting reagent strong base problem i strong B to strong A ii strong A …