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Multimedia Chemistry I & II (1996-9-11) [English].img
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chapt11.1c
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à 11.1cèAcid - Base Defïitions
äèPlease identify ê Arrhenius acids å bases among ê followïg species.
âèWhich ç ê followïg compounds acts as an Arrhenius acid;
which as an Arrhenius base: HBr, NaH, Li╖O, å Cl╖O╝?èHBr å Cl╖O╝
generate Hó ions ï water å are acids.èNaH å Li╖O generate OHú ions
ï water å are bases.
éSèArrhenius acids dissociate ï water ë release Hó ions.èCommon
acids are ê nonmetallic hydrides, nonmetallic oxides, å oxoacids.
The nonmetallic hydrides are bïary acids; such as, HCl, HBr, å H╖S.
The nonmetallic oxides dissolve ï water ë form oxoacids; for example,
SO╕ forms H╖SO╣.èThese compounds dissociate ïèwater ë ïcrease ê Hó
ion concentration.
H╖O
HCl(g) ─────¥ Hó(aq) + Clú(aq).
H╖O H╖O
H╖S(g) ─────¥ Hó(aq) + HSú(aq) ─────¥ 2Hó(aq) + Sìú(aq).
SO╕(g) + H╖O ───¥ H╖SO╣(aq) ───¥ 2Hó(aq) + SO╣ìú(aq).
N╖O║(g) + H╖O ───¥ 2HNO╕(aq) ───¥ 2Hó(aq) + 2NO╕ú(aq).
Arrhenius bases dissociate ï water ë release hydroxide ions, OHú.
Metallic hydroxides, metallic oxides, å metallic hydrides act as bases.
We are most familiar with ê hydroxides.
H╖O
NaOH(s) ─────¥ Naó(aq) + OHú(aq).
Most metallic oxides are ïsoluble, but when ê oxide dissolves it can
be considered ë form a hydroxide, which dissociates.
K½O + H╖O ───¥ 2KOH ───¥ 2Kó(aq) + 2OHú(aq).
The oxide ion is relatively small which ïtensifies ê effect ç its
negative charge.èIt attracts proëns from H╖O ë form ê hydroxide ion.
Oìú + H╖O ───¥ 2OHú.
Consequently metallic oxides are bases.èThe nonmetallic oxides are
acidic because ê nonmetal aëm attracts ê electrons on ê oxygen ï
ê water molecule.èThe H-O bond is weakened, å Hó is released.
The metallic hydrides are basic because ê hydride ion, Hú, can share an
electron pair.
è Hú + H╖O ───¥ H╖(g) + OHú.
1èWhich list ç compounds contaïs only Arrhenius acids?
A) LiH, H½Se, HI B) NiO, Al╖O╕, CO╖
C) CaH╖, Ba(OH)╖, HIO╕ D) HBr, SO╖, HClO╣
üèNonmetallic hydrides, nonmetallic oxides, å oxoacids behave
as Arrhenius acids.èFormulas ç oxoacids start with H å contaï a
nonmetal aëm å one or more oxygen aëms.èHBr is a nonmetallic hydride.
SO╖ is a nonmetallic oxide.èHClO╣ is an oxoacid.
Ç D
2èWhich list ç compounds contaïs only Arrhenius bases?
A) CuO, Ni(OH)╖, ClO╖ B) Na╖O, MgH╖, KOH
C) P╣O╢╡, HBr, HIO╕ D) H╖S, H╖CO╕, Fe(OH)╕
üèMetallic oxides, metallic hydroxides, å metallic hydrides act
as Arrhenius bases.èNa╖O is a metallic oxide, which dissolves ï water
ë form sodium hydroxide.èMgH╖ is a metallic hydride, which reacts with
water ë form magnesium hydroxide å hydrogen gas.èKOH is potassium
hydroxide, which obviously contaïs hydroxide ions.
Ç B
äèPlease identify ê Bronsted-Lowry acids, bases, conjugate acids å/or conjugate bases ï ê followïg reactions.
âèWhat are ê acids å bases ï ê equilibrium reaction:
NH╖ú + C╖H╖ = C╖Hú + NH╕?èA Bronsted acid releases Hó; bases accept Hó.
NH╖ú accepts Hó when formïg NH╕.èC╖H╖ donates Hó when formïg C╖Hú.
NH╖ú is a Bronsted base; NH╕ is ê conjugate acid ç NH╖ú.èC½H½ is
a Bronsted acid; C½Hú is ê conjugate base ç C╖H╖.
éSèThe Arrhenius defïition ç acids å bases is satisfacëry for
aqueous solutions.èA more general defïition ç acids å bases is needed
for nonaqueous conditions.èThe Bronsted-Lowry system focuses on ê
transfers ç proëns.
A Bronsted-Lowry (B-L) acid donates proëns.
A Bronsted-Lowry base accepts proëns.
In this system, ê hydroxide ion is a base because it accepts a proën
when it forms water.èCan you identify ê B-L acid å base ï ê
reaction:
C╖H║ú + CH╕OH = C╖H╗ + CH╕Oú?
By comparïg ê formulas ç ê reactant with those ç ê products, we
observe that C╖H║ú gaïs Hó å forms C╖H╗, so C╖H║ú is ê base.
CH╕OH donates Hó å forms CH╕Oú, so CH╕OH is ê acid.
If ê reaction occurred ï ê reverse direction, ê C╖H╗ would act as
ê acid å CH╕Oú would be ê base.èIn ê given reaction, C╖H╗ is ê
conjugate base ç C╖H║ú, å CH╕Oú is ê conjugate base ç CH╕OH.
C╖H║ú å C╖H╗ comprise one B-L acid-base pair, å CH╕OH å CH╕Oú make-
up ê oêr B-L acid-base pair.èRecognizïg acid-base pairs assists us
ï underståïg what type ç reaction has occurred å ï predictïg
possible outcomes ç acid-base reactions.èThe formula ç ê conjugate
base ç an acid is obtaïed by subtractïg Hó from ê formula ç ê
acid.èThe formula ç ê conjugate acid ç a base is obtaïed by addïg
Hó ë ê formula ç ê base.
What is ê conjugate acid ç ê OHú ion?èAnswer: H½O.
èè(OHú + Hó = H½O)
What is ê conjugate base ç HPO╣ìú?èAnswer: PO╣Äú.
èèè (HPO╣ìú - Hó =èPO╣Äú)
One last example: what are ê acid, ê base, ê conjugate acid å ê
conjugate base ï ê reaction:
èèèè (CH╕CH╖)╖NH + C╗H║SO╕H = (CH╕CH╖)╖NH╖ó + C╗H║SO╕ú?
At first this might look messy, but notice that êre ï one H on ê N
ï ê first reactant å two H's on ê N ï ê first product.èAlso
ê charge on ê compound went from neutral ë plus one. (CH╕CH╖)╖NH
gaïed a proën; it must be ê base.èIf (CH╕CH╖)╖NH is ê base, ên
C╗H║SO╕H must be ê acid.
(CH╕CH╖)╖NH is ê base, å (CH╕CH╖)╖NH½ó is ê conjugate acid.
C╗H║SO╕H is ê acid, å C╗H║SO╕ú is ê conjugate base.
3èWhat is ê acid-conjugate base pair ï ê equilibrium:
H╖C╖O╣ + H╖O = H╕Oó + HC╖O╣ú?
A) H╖C╖O╣ - H╕Oó B) H╖C╖O╣ - HC╖O╣ú
C) H╖O - H╕Oó D) H╖O - HC╖O╣ú
üèThe acid loses Hó.èComparïg H╖C╖O╣ with ê products, we see
that it lost Hó å formed HC╖O╣ú.èH╖C╖O╣ is ê acid, å HC╖O╣ú is ê
conjugate base.èWhen comparïg species we look at match up aëms oêr
than hydrogen.èIn this reaction, we traced ê "C╖O╣" unit through ê
reactants ë ê products.
Ç B
4èWhat is ê acid-conjugate base pair ï ê equilibrium:
CO╕ìú + H╖O = HCO╕ú + OHú?
A) CO╕ìú - HCO╕ú B) CO╕ìú - OHú
C) H╖O - HCO╕ú D) H╖O - OHú
üèThe acid loses Hó å ê conjugate base ê species left after
removïg Hó from ê acid.èCO╕ìúèhas gaïed a proën å formed HCO╕ú.
CO╕ìú is ê base.èH╖O has lost Hó å has formed OHú.èH╖O is ê acid
å OHú is its conjugate base.
Ç D
5èWhat is ê base-conjugate acid pair ï ê equilibrium:
CH╕OH + C╗H║ú = CH╕Oú + C╗H╗?
A) CH╕OH - C╗H╗ B) CH╕OH - CH╕Oú
C) C╗H║ú - C╗H╗ D) C╗H║ú - CH╕Oú
üèThe base gaïs Hó ï an acid-base reaction.èCH╕OH loses Hó å
forms CH╕Oú.èC╗H║ú gaïs Hó å forms C╗H╗.èC╗H║ú is ê base å C╗H╗
is its conjugate acid.èWe tracked ê C╗ unit ï this reaction
Ç C.
6èWhat is ê base-conjugate acid pair ï ê equilibrium:
NO╖ú + HSO╣ú = HNO╖ + SO╣ìú?
A) NO╖ú - HNO╖ B) NO╖ú - SO╣ìú
C) HSO╣ú - HNO╖ D) HSO╣ú - SO╣ìú
üèThe base gaïs Hó ï an acid-base reaction.èComparïg ê
nitrogen contaïïg species among ê reactants å ê products, NO╖ú
å HNO╖, we see that NO╖ú has gaïed Hó.èWe conclude that NO╖ú is ê
base.èHNO╖ is ê conjugate acid ç NO╖ú.
Ç A
7èWhat is ê conjugate base ç H╖O╖ (hydrogen peroxide)?
A) H╖OèèèèB) H╖O╖úèèèèC) HO╖úèèèèD) OHú
üèWhen we want ë know ê conjugate base ç H╖O╖, we know ë
write a reaction showïg H╖O╖ actïg as an acid.èWhen an acid loses a
proën, ê remaïïg species is ê conjugate base.èFor hydrogen per-
oxide ê acidic reaction isèH╖O╖ ──¥ Hó + HO╖ú.èThe conjugate base is
HO╖ú.
Ç C
8èWhat is ê conjugate base ç H╖PO╣ú?
A) H╕PO╣èèèè B) H╕OóèèèèC) HPO╣ìúèèèè D) OHú
üèWhen H╖PO╣ú acts as an acid by donatïg Hó, ê remaïïg ion is
ê conjugate base.èWe need ë write a reaction showïg H╖PO╣ú givïg
up a proën, Hó.èH╖PO╣ú ──¥ Hó + HPO╣ìú.èRemember ê aëms å ê
charge must balance.èThe conjugate base ç H╖PO╣ú is HPO╣ìú.
Ç C
9èWhat is ê conjugate acid ç NH╕?
A) NH╣óèèèèB) NH╖úèèèèC) NH╕óèèèè D) H╕Oó
üèIn ê Bronsted-Lowry system, we have acid-conjugate base å
base-conjugate acid pairs.èTo write ê formula ç ê conjugate acid
we must consider ê compound actïg as a base.èBases accept Hó.
When NH╕ gaïs a proën, it becomes NH╣ó.èNH╣ó is ê conjugate acid ç
NH╕.
Ç A
10è What is ê conjugate acid ç HSO╕ú?
A) HSO╕óèèèèB) SO╕ìúèèèèC) H╖SO╕èèèèD)SO╣ìú
üèThe conjugate acid ç HSO╕ú is ê ion or molecule that results
when HSO╕ú accepts a proën.èYou should write a reaction ë show HSO╕ú
actïg as a base.èHSO╕ú + Hó ──¥ H╖SO╕.èThe conjugate acid çèHSO╕ú is
H╖SO╕.
Ç C
11èWhat is ê conjugate acid ç H╖O?
A) H╖Oóèèèè B) H╕OóèèèèC) H╖óèèèèD) OHú
üèWhen a species acts as a base ê new species formed is ê con-
jugate acid.èWhen water accepts a proën, ê hydronium ion, H╕Oó, is
formed.èH╕Oó is ê conjugate acid ç H╖O.
Ç B
12èWhat is ê conjugate base ç H╖O?
A) H╖OúèèèèB) Húèèè C) OHúèèèèD) Oìú
üèWhen water acts as an acid ê remaïïg species is ê conjugate
base.èAcids donate Hó.èThe followïg reaction shows water actïg as an
acid:èH╖O ──¥ Hó + OHú.èThe conjugate base ç water is OHú.
Ç C