ACID-BASETHEORY
:.- \
l.
(a) Give the Arrhenius definition of an acid- release
hydrogen
ionswhendissolved
in water
O) Give a balanced equation for the ionization of a t)ryical Arrhenius acid such as I{2S.
H2S --IEEI' 2 H+1*y +s21*y
2.
(a) Give the Arhenius definition of anbaserelease
hydroxide
ionswhendissolved
h water
(b) Give a balancedequationfor the ionizationof a typical Arrheniusbase$rch asCa(OtDz.
+ z oril6q1
cu(oloz .--!49L ca2+12,q
3. (a) Give the Brdnsted-Lowryor protontransferdefinition ofan acid.
a protonor hydmg!nion donor
O) Give a balancedequationfor the protontransferreactionofa typical Brdnsted-Lowryacid
zuchasHCI with water.
+ H2o61+r H3e+1r4+ crllaq;
"dkrl
(.) Identiff the conjugateacid/basepairsin t&is syskm.
.,
i
I
'
acid I base2
acid2
baseI
(d) What is presentin this systemwhich accountsfor the acidity of the solution?It' ions
(e) Namethe two Briinsted-Lowry acidspresentin this equilibrium system.HCkg)& H3o+130;
(D Namethe two Brtinsted-Lowrybasespresentin this equilibrium system.H2o0 & crl6y
4.
(a) Give the Br6nsted-Lowryor protontransferdefinition of a base.
a protonor hydrog!rxion accepbr
.-\
**#
.
(b) Give a balancedequationfor the protontransferreactionof a typical Brtinsted-Lowrybase
suohasNH3 with water.
NH3G) + H2Oq).' NH+a1sd+ orllaq)
(c) Identiff the conjugateacid/basepairsin this system.
tas! 1
acid?
acid I
base2
(d) What is presentin this systemwhich accouits for the basicity of the solution?oH-l ions
(e) Couldthe Arrheniustheory accountfor this basicity?.Explain.
No, sincethe NH3 moleculeiloesnot contsinhyilroxide ions which canbe releasedupon dissolving.
(f) Namethe two Br6nsted-Lowryacidspresentin this equilibrium system.H2o(l)& NH+4(ac)
(g) Naniethe two Briinsted-Inwry basespresentin this equilibrium system- NH31g1g oH-l(aq)
5. Considerthe dissolvingof pure H2SOain pure HC2H3O2.
+ HCzHrOz'- HSO41+ H2C2fuOl
HzSOq
(a)Identiffthec"l:[ti"*'#s"o*t'
ou,"I
acid2
(b) Would this reactionbe consideredanacid/basereactionunderArrheniusTheory?Explain.
No, becausehydmg!nions arenot rcactingwith hydmxideions andfi[thermore no Arhenius baseis presenl
\-
.)
6. Write anequationfor eachof the following reactions.Identiff the acidsandbases.Indicateone
conjugatepair by drawingboxesaroundtheir formulasandthe other conjugatepair by circling
them.
\.
(a) H3POaactingasa Brdnstedacid in an aqueoussolution
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:
(b) C2H3O'1 acting as a Bronsted basein an aqueoussolution.
(c) theprotontransferreactioninvolvingthe acidffCOrl andthe baset0i
(d) the nonaqueousreaction in which hydrogen nitrate acts as a base and sulphuric acid acts as
an acid.
7.
.-'l
'*ite!
NaOH is a baseand HCIO3 is an acid. Eachhas an O-H covalent bond. Where the bondsbreak
upon ionization in water accountsfor whether or not they are acids or bases.
(a) Draw an electron dot diagram for each.
oa aa oa
-1
.Itp.t
{
t-']
:oao:cl:o
:H
aa aa
: ao
o:
uot ft'
(b) Accountfor thebondbreakingbetweentheNa andthe O-H in NaOH andbetweenthe O and
theH in HCIO3.
In NaOH the individual Na+ and OH-l ions have a full charge and are separatedfrom each other. As as result they
experience much stronger atfactions to polar water molecules then does the polar OH bond which only has small
partial charges on the O and the H. In HCIO3 the oxygen atoms which are not bonded to the hydrogen, draw the
electron in the OH bond away from the hydrogen nucleus becauseof their higher electronegativity. This creates a
highly polar OH bond which then experiences strong dipole-dipole forces of attraction with the polar water
molecule and the OH bond breaks.
8. (a) Write equilibriumreactionequationsfor the dissociationof HNO3 andHNOZ in water.
(b) Identiff the conjugateacid-basepairsfor the forwardandreversereactions.
HNOI + H2,Oj'NO-l: (ad + gfO*l(uq)
acid}
acidl basb2 basel
.*
HNOZ+ H2O NO-12(ad + g:O*l(uq)
acid?
acidl base2 basel
(c) Since both systems test as decidedly acidic with litmus, to which side of the reaction
equation do each of the equilibria lie? the right
(d) Identiff the sftonger acid in each equilibrium. HNog andHNo2
(e) Identify the stronger base in each equilibrium. water
(f) GivetheElectronDot Drawingfor eachof tiltto3 andHI.{OZ.
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aa
o : : N :O :H
a.
o ::N:O:H
:9.:
..
al
..
-.
aa
|
..
t.
|
(g) Give a PerspectiveDrawing for eachof HNO3 and HNOZ.
I
;'o
'l
N
N
O1
\
o
/\o
(h) On the basis of molecular structures,electronegativitiesand bond polarities, which of HNO3
and HNO2 will have the more polar O-H bond?HNol
(i) Predict the relative acid strengthsof HNO3 and HNO2. Explain.
thanthatof
HNO3will havethegreateracidsfrengthsinceits morepolarOHbondwill breakto a greaterdegreee
HNO2 when experiencing the athactions from the polar water solvent molecules.
9. In orderfor a moleculesuchasIIF to ionizein water,the H-F bondmust be brokenandeachof
the ions createdmustbe solvated.Eachofthesestepsinvolves energybeing gainedor lost.
(a) In which hydrogenhalide,IIF or HI will thehydrogenhalidebondrequiremoreenergyto be
broken?Explain.
HF. The snull sizeofthe fluorine atomallows the hydrogento be held closerto the fluorine nucleusandthqefore
more tighdy.
{
)
@) The I{ ion will releasemoreenergywhensolvatedby a watermoleculerhanwill the F-l ion.
release.
Discusstwo factorsthat conhibuteto this energ5r
The higherchargedeneityofthe smallerFl ion shouldrcsultir r gr!stersolvationencrgyhowwcrthe larger size of
the fl ion will permit a larger numberof water nolccules to solvatethe ion. Eachadditional solvatingwst!r
moleculeresulb is a firther enerry loss.
(c) Explain how the abovetwo frctors contributeto the acid strengthof thrchydrogenhalides.
The greatestnet en!rgr lossoccurswith the ionizationofHI andthusthe acid strengthis greater.
10. Someacidsarepollprotic, i.e. they havemorethanoneproton availablefor donatioq eg.
H2SO4.The loss of theseprotonsmay occurin successivesteps.
(a) Write the ionization equationfor the Briinsted-Lowryacid H2SOadonatingoneprcton.
H2sO4(ad + H2OG)" HSO4(aq)-t + H3O+l(uq)
@) Identiff the conjugateacid/basepairs.
acid I
base2
baseI
asid2
(c) Identiff tle productof the abovereactionthat could function as either a Brdnsted-Lowry
acid or base.ttso4:r
(d) Write the ionizationequationfor the aboveproductdonatingits remainingprotonasa
Br6nsted-Iowry acid.
Hsoa{ + H2o6;.- So41*;-2+ H3O+l1rn1
(e) Identiff the conjugateacid/basepairs.
aoid I
base2
baseI
scid?
(f) Offer an explanationfor why the reactionin (a) is more acidic than that in (d).
'' . -/
After the first Foton is domted,the secondprotonmustbe removedfrom a fully negativelychargedion which
exertsgreateratbactionaadmekesit nore difficult for the protonto be donatcd.
LastRevised517109