LiroxtronIV (LiroxtronIV)-
what is Arrhenius theory of acids and bases?
Arrhenius acid; formula has H, ionises in H2O to give H+(aq)
Arrhenius base; formula has OH, ionises in H2O to give OH-(aq)
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what is Bronsted-Lowry theory of acids and bases?
Bronsted acid; proton(H+) donor
Bronsted base; proton(H+) acceptor
BABBDA
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what are Lewis acids and bases?
Lewis acid; electron pair acceptor
Lewis base; electron pair donor
LALBAD
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what are conjugate acids and bases?
a conjugate acid-base pair differ by a transferrable atom; conjugate acid(from base accepting H+), conjugate base(from acid donating H+)
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differentiate between strong acids & bases and weak acids & bases
strong acids & bases; ionise completely in aqueous soln(→)
weak acids & bases; ionise partially in aqueous soln(⇌)
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explain pH
pH = -lg[H+], [H+] = 10-pH
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explain pOH
pOH = -lg[OH-], [OH-] = 10-pOH
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explain Ka
acid dissociation constant,
↑ as acid strength ↑
given HA(aq) + H2O(l) ⇌ A-(aq) + H3O+(aq)
Ka = [H3O+][A-] / [HA]
varies w/ temp
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explain pKa
pKa = -lgKa
↑ as acid strength ↓
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calculate pH(weak acid)
given HA(aq) + H2O(l) ⇌ A-(aq) + H3O+(aq)
Ka = [H3O+][A-] / [HA]
Ka = x2 / c - x, assume x << c
Ka = x2 / c, so
[H+] = sqroot(Ka x c)
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explain Kb
base dissociation constant,
↑ as base strength ↑
given A(aq) + H2O(l) ⇌ BH+(aq) + OH-(aq)
Kb = [BH+][OH-] / A
varies w/ temp
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explain pKb
pKb = -lgKb
↑ as base strength ↓
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calculate pH(weak base)
given A(aq) + H2O(l) ⇌ BH+(aq) + OH-(aq)
Kb = [BH+][OH-] / A
Kb = x2 / c - x, assume x << c
Ka = x2 / c, so
[OH-] = sqroot(Kb x c)
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explain Kw
for any conjugate base pair,
Ka x Kb = Kw = 1.00x10-14mol2dm-6(25oC)
pKa + pKb = pKw = 14(25oC)
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what is a buffer?
buffer soln is one which resists pH change when small amount of acid or base added
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explain acidic buffer
weak acid + salt(conjugate base)
small [H+] added, removed by reacting w/ conjugate base ions
small [OH-] added, removed by reacting w/ acid molecules
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explain alkaline buffer
weak base + salt(conjugate acid)
small [H+] added, removed by reacting w/ base molecules
small [OH-] added, removed by reacting w/ conjugate acid ions
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calculate pH of acidic buffer
Ka = [salt][H+] / [acid], so
pH = pKa + lg([salt]/[acid])
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calculate pH of alkaline buffer
Ka = [salt][OH-] / [base], so
pOH = pKb + lg([salt]/[base])
then apply pH = pKw - pOH
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what is equivalence point?
exact point during titration when reaction b/w acid & base is just complete(soln contains only salt)
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what is end-point?
point during titration when distinct colour change observed, brought about by use of suitable indicator
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describe titration of strong acid against strong base
initial pH = pH of SA
SB slowly added, reacts w/ SA form neutral salt >
resultant soln contains unreacted SA & neutral salt >
pH relatively low
pH ↑ sharply around equivalence pt >
pH @ equivalence pt = 7, resulting soln contains only neutral salt
after equivalence pt, pH ↑ slowly, excess SB added, tends towards pH of SB
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describe titration of weak acid against strong base
initial pH = pH of WA
SB slowly added, reacts w/ WA form basic salt >
resultant soln contains unreacted WA & conjugate base, acidic buffer region formed before equivalence pt >
@ 1/2Veq, 1/2 n(WA) reacted form same n(conjugate base of WA) >
pH = pKa as [salt] = [acid]
max buffering capacity @ 1/2Veq
pH ↑ sharply around equivalence pt, >7 @ equivalence pt as resultant soln contains only basic salt, hydrolyses in H2O to give OH-
after equivalence pt, pH ↑ slowly, excess SB added, tends towards pH of SB
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describe titration of weak base against strong acid
initial pH = pH of WB
SA slowly added, reacts w/ WB form acidic salt >
resultant mixture contains unredacted WB & conjugate acid, alkaline buffer region formed before equivalence pt >
@ 1/2Veq, 1/2 n(WB) reacted form same n(conjugate acid of WB) >
pOH = pKb as [salt] = [base]
max buffering capacity @ 1/2Veq
pH ↓ sharply around equivalence pt, <7 @ equivalence pt as resultant soln contains only acidic salt, hydrolyses in H2O to give H+
after equivalence pt, pH ↓ slowly, excess SA added, tends towards pH of SA
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describe titration of weak acid against weak base
initial pH = pH of WA
pH ↑ steadily, WB added gradually
no sharp change in pH around equivalence pt(no suitable indicator), pH @ equivalence pt @ 7 or <7(Ka>Kb) or >7(Ka<Kb)
after equivalence pt, pH ↑ slowly, tends towards pH of WB
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explain choice of suitable indicators for acid-base titrations
suitable indicator = one which changes colour sharply as close as possible to pH of equivalence pt; suitable if
working pH range coincides w/ sharp change in pH near equivalence pt OR
pKind of indicator closest to equivalence pt of titration
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describe, explain uses of buffer solutions in controlling pH of blood
buffer regulating blood pH is (H2CO3 / HCO3-)buffer system, maintains blood pH @ 7.4
does not operate @ MBC as [HCO3-] ≠ [ H2CO3]
better buffer @ removing additional H+ as [HCO3-] >> [ H2CO3]
[H+] in blood ↑, resist pH change by
HCO3-(aq) + H+(aq) → H2CO3(aq)
if [OH-] in blood ↓, resist pH change by
H2CO3(aq) + OH-(aq) → H2O(l) + HCO3-(aq)
