2022 H1_Theories of acids and bases_Self check and Tutorial (teacher).doc

St.Andrew’sJuniorCollegeH1Chemistry2022PhysicalChemistryTutorialTheoriesofAcidsandBasesSELF-CHECKQUESTIONS 1. Identifytheconjugateacid-basepairinthefollowingreaction.HCl +NaHCO3 → H2 CO3 + NaCl 2. CalculatethepHofsolutionswiththefollowingH3 O + concentrationsinmol dm –3 (a) 6.80x10 –3 (b) 3.20x10 –5 3. CalculatethepHofsolutionswiththefollowingOH – concentrationsinmol dm –3 (a) 3.70x10 –10 (b) 6.40x10 –5 4. CalculatetheH3 O + andOH – concentrationsinsolutionswiththefollowingpHvalues:(a) 9.21 (b) 13.7 5. CalculatethepHandpOHofthefollowingsolutions:(a) 25cm 3 of0.200mol dm –3 ofhydrochloricacidmadeupto500cm 3 ofsolution.(b) 1.00 g of calciumhydroxide dissolved in water and made up to 250 cm 3 ofsolution 6. Explainthefollowingterms:(i)pH (ii) Ka (iii) Kb (iv) Kw 7. Calculatethedegreeof dissociationoftheweakmonobasicacidslistedbelow:(a) asolutionof0.0100mol dm –3 CH3 COOHhasapHof3.38.(b) asolutionof0.200mol dm –3 HCNhasapHof5.05 8. Calculatethepercentagedissociationoftheweakmonoacidicbaseslistedbelow:(a) asolutionof0.0100mol dm –3 CH3 NH2 has[OH – ]of4.78x10 –7 mol dm –3 .(b) asolutionof0.0500mol dm –3 C6 H5 NH2 has[OH – ]of9.65x10 –5 mol dm –3 1

9. (a)Stateifeachofthefollowingsaltsisacidic,basicorneutral.A–acidicsalt;B–basicsalt;N–neutral saltSalt A,BorN Salt A,BorN(i) KBr (iv) (C6 H5 NH3 )2 SO4 (ii) C6 H5 ONa (v) (CH3 )2 NH2 Br(iii) NaCN (vi) CH3 COOK (b) (i)ForC6 H5 O – Na + ,writeanequationtoillustrateitsacidity/basicity.(ii)ForCH3 NH3 Cl,writeanequationtoillustrateitsacidity/basicity. 10. Indicateifthesolutioncontainingthespecifiedspeciesisabuffersolution.Ifitis,stateifitisacidicorbasicbuffer.X:notbuffer A:acidicbuffer B:basicbuffer Solution XorAorB(a) CH3 COOH/CH3 COONa(b) CH3 COOH/NaCl(c) HCl/NaCl(d) HNO3 /NaNO3 (e) HCN/KCN(f) NH3 /NH4 NO3 (g) NaOH/Na2 SO4 ANSWERS2 (a)2.17(b)4.49 3 (a)4.57(b)9.81 4 (a)[H3 O + ]=6.17x10 –10 mol dm −3 ;[OH - ]=1.62x10 –5 mol dm −3 (b)[H3 O + ]=2.00x10 –14 mol dm −3 ;[OH - ]=0.500mol dm −3 5 (a)pH=2;pOH=12.(b)pOH=0.967;pH=13.0 7 (a) α=0.04(b) α=4.46x10 -5 8 α=4.78x10 −3 %α=0.193% 9 (a)(i)N(ii)B(iii)B(iv)A(v)A(vi)B 10 (a)A(b)X(c)X(d)X(e)A(f)B(g)X 2

Self–CheckAnswers: 1. Identify the Bronsted acid and its conjugate base and the Bronsted base and itsconjugateacidinthefollowing:HCl + NH3 → NH4 + + Cl − acid base conjugateacid conjugatebase 2 ApplyingpH=-log[H + ]orpH=-log[H3 O + ](a)2.17(b)4.49 3 ApplyingpOH=-log[OH - ]FollowedbypH=14–pH(a)4.57(b)9.81 4 (a)[H3 O + ]=10 -9.21 =6.17x10 –10 mol dm −3 [OH - ]=10 -14 /[H3 O + ]= 1.62x10 –5 mol dm −3 (b)[H3 O + ]=10 -13.7 =2.00x10 –14 mol dm −3 [OH - ]=10 -14 /[H3 O + ]= 0.500mol dm −3 5 (a)[HCl]=[H + ]=[(25/1000)x0.2]/(500/1000)=0.01mol dm -3 pH=-log[H + ]=2pOH=14–2=12. (b)moleofcalciumhydroxide=1.00/[40.1+2(17)]=0.0135molMol ofOH - ions=0.0270[OH - ]=0.0270/250x1000=0.108mol dm -3 pOH=-log[OH - ]=0.967pH=14–0.967=13.0 6 (i)pH=−lg[H + ] (ii)ForaweakacidHA,HA(aq)+H2 O(l) A − (aq)+H3 O + (aq) Ka = moldm −3 . (iii)ForaweakbaseB,B(aq)+H2 O(l) BH + (aq)+OH − (aq) Kb = mol