2022_H1_Theories of acids and bases_notes (teacher).doc

St.Andrew’sJuniorCollegeH1Chemistry2022LectureNotesTheoriesofAcidsandBases AssessmentObjectives Candidatesshouldbeableto:(a) showunderstandingof,andapplytheArrheniustheoryofacidsandbases(b) showunderstandingof,andapplytheBronsted-Lowrytheoryofacidsandbases,includingtheconceptofconjugateacidsandbases;(c) explainqualitativelythedifferencesinbehaviourbetweenstrongandweakacidsandbasesintermsoftheextentofdissociation;(d) explainthetermspH;Ka ;Kb ;Kw [TherelationshipKw =Ka Kb isnotrequired];(e) calculate[H + (aq)]andpHvaluesforstrongacids,andstrongbases;(f) explainthechoiceofsuitableindicatorsforacid-basetitrations,givenappropriatedata,intermsofthestrengthsoftheacidsandbases;(g) (i)explainhowbuffersolutionscontrol pH;(ii)describeandexplaintheusesofbuffers,includingtheroleofH2 CO3 /HCO3 - incontrollingpHinblood. LectureOutline:1. Theoriesofacidsandbases2. Autoionisationofwater3. Dissociationofweakacidandbases4. Acid-BasePropertiesofSaltSolutions5. Indicatorsforacid-basetitrations6. MonoproticAcid-BaseTitrationCurves7. Buffersolutions References:1. ChemistrybySilberberg2. ChemistrybyRaymondChang3. ChemistryforAdvancedlevel byPeterCann4. ChemistryincontextbyHill andHolman5. A–level ChemistrybyRamsden 1

1. THEORIESOFACIDSANDBASES 1.1 ArrheniustheoryofacidsandbasesAnArrheniusacidisasubstancethatproducesH + inaqueoussolution.AnArrheniusbaseisasubstancethatproducesOH – inaqueoussolution. E.g.: HNO3 (l) + H2 O(l) NO3 – (aq) + H3 O + (aq)Note: H3 O + ishydroniumion, whichisthesameasH + (aq) NaOH(s) + aq Na + (aq) + OH – (aq) ● Anacid-basereactioninvolvestheformationofsaltandwater 1.2 Brønsted–LowrytheoryofacidsandbasesABrønsted–Lowryacidisaproton(H + )donor.ABrønsted–Lowrybaseisaproton(H + )acceptor. base conjugateacid E.g.: NH3 (aq) + H2 O(l) NH4 + (aq) + OH – (aq) Acid conjugatebase base conjugateacid E.g.: HCl(g) + NH3 (g) NH4 Cl(s) acid conjugatebase ● Anacid–basereactioninvolvesthetransferofaprotonfromtheacidtothebase.● When a Brønsted–Lowry acid (HA) loses a proton, the resulting product (A – ) iscalledtheconjugatebaseofHA. 2

● WhenaBrønsted–Lowrybase(B)acceptsaproton,theresultingproduct(BH + )iscalledtheconjugateacidofB.● Aconjugateacid-basepairdiffersbyaH + . Examplesofconjugatepairs:HCl/Cl – NH3 /NH4 + H2 O/OH – H2 O/H3 O + CH3 COOH/CH3 COO – CH3 NH2 /CH3 NH3 + Exercise1Identifytheacid,base,conjugateacidandconjugatebaseinthefollowingreactions: a) CH3 COOH + H2 O CH3 COO – + H3 O + acid base conjugatebase conjugateacidb) CH3 COOH + HCl CH3 COOH2 + + Cl – base acid conjugateacid conjugatebasec) HNO3 + H2 O NO3 – + H3 O + acid base conjugatebase conjugateacidd) HNO3 + H2 SO4 HSO4 – + H2 NO3 + base acid conjugatebase conjugateacid 👉Self–Check:Q1💪InSummary💪Arrhenius Brønsted-LowryAcids producesH + inwater donatesH + Bases producesOH – inwater accepts H + 3

1.3 StrengthofAcidsandBases Strongacidcompletelydissociatesinwater.E.g.: HCl(g) +aq H + (aq) + Cl – (aq)Mostmineral acidsarestrongacids.E.g.:HI,HBr,H2 SO4 ,HNO3 etc.representscompletedissociat