acid and bases. acid-base theories 1 of 2 the most general theory for common aqueous acids and bases...
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AcidAcid andand Bases Bases
AcidAcid andand Bases Bases
AcidAcid andand Bases Bases
AcidAcid andand Bases Bases
17.2 Know the two theories for acids/bases
Know how to identify: 1. an acid 2. a base 3. a conjugate acid 4. a conjugate base
ACID-BASE THEORIES ACID-BASE THEORIES 1 of 21 of 2 • The most general theory for common The most general theory for common
aqueous acids and bases is the aqueous acids and bases is the BRØNSTED - LOWRY theoryBRØNSTED - LOWRY theory
• ACIDS DONATE HACIDS DONATE H++ IONS IONS
• BASES ACCEPT HBASES ACCEPT H++ IONS IONS
Conjugate acidConjugate base
Conjugate acid Conjugate base
Conjugate acid
Conjugate base
Conjugate acid
Conjugate base
Acetic Acid
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Lewis acidLewis acid a substance that accepts an a substance that accepts an
electron pairelectron pair
Lewis Lewis basebase a substance that a substance that donates an electron pairdonates an electron pair
17.9
ACID-BASE THEORIES 2ACID-BASE THEORIES 2 of 2 of 2
17.3 A common way to express acidity is with pHA common way to express acidity is with pH
pH = -log [HpH = -log [H33OO++] ] = -log [H= -log [H++]]In a neutral solution, In a neutral solution,
[H[H3OO++] = [OH] = [OH--] = 1.00 x 10] = 1.00 x 10-7-7 at 25 at 25 ooCC
pH = -log (1.00 x 10pH = -log (1.00 x 10-7-7) ) = - (-7) = 7= - (-7) = 7
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In pure water there is In pure water there is AUTOIONIZATIONAUTOIONIZATION
Equilibrium constant for autoion = KEquilibrium constant for autoion = Kww
KKww = [H = [H33OO++] [OH] [OH--] = ] = 1.00 x 101.00 x 10-14-14 at 25 at 25 ooCC
Other pX ScalesOther pX ScalesIn generalIn general pX = -log XpX = -log X
and so and so pOH = - log [OHpOH = - log [OH--]] KKww = [H = [H3OO++] [OH] [OH--] = 1.00 x 10] = 1.00 x 10-14-14 at 25 at 25 ooCC
Take the log of both sidesTake the log of both sides
-log (10-log (10-14-14) = - log [H) = - log [H3OO++] + (-log [OH] + (-log [OH--])])
pKpKww = 14 = pH + pOH = 14 = pH + pOH
The pH ScaleThe pH Scale
AddingBasic Substance
AddingAcidic Substance
Pure Water@ 25oC
Strong AcidsStrong Acids• Generally divide acids and bases into STRONG Generally divide acids and bases into STRONG
or WEAK ones.or WEAK ones.
STRONG ACID:STRONG ACID: HNO HNO33(aq) + H(aq) + H22O(l) O(l) HH33OO++(aq) + NO(aq) + NO33
--(aq)(aq)
HNOHNO33 is about 100% dissociated in water. is about 100% dissociated in water.
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• Strong Base:Strong Base: 100% dissociated in water. 100% dissociated in water. NaOH(s) NaNaOH(s) Na++(aq) + OH(aq) + OH--(aq)(aq)
Strong BasesStrong Bases
Other common strong bases Other common strong bases include KOH and include KOH and Ca(OH)Ca(OH)22
H2O
Do Strong acid Strong base problems
• Weak acids are Weak acids are much less than 100% ionized much less than 100% ionized in in water.water.
One of the best known is acetic acid: CHOne of the best known is acetic acid: CH33COCO22HH
Weak AcidsWeak Acids
• Weak base:Weak base: less than 100% ionized in less than 100% ionized in waterwater
One of the best known weak bases is One of the best known weak bases is ammoniaammonia
NHNH33(aq) + H(aq) + H22O(l) NHO(l) NH44++(aq) + OH(aq) + OH--(aq)(aq)
Weak BasesWeak Bases
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17.4, 17.7 For equilibrium constants of weak acids and bases, know how to: Define Ka & Kb How to use to determine eq. conc. Determine pKa, pKb
Equilibrium Constants Equilibrium Constants for Weak Acidsfor Weak Acids
Weak acid has KWeak acid has Kaa < 1 < 1 Leads to small [HLeads to small [H33OO++] and a pH of 2 - 7 ] and a pH of 2 - 7
Model Weak Acid
Equilibrium Constants Equilibrium Constants for Weak Basesfor Weak Bases
Weak base has KWeak base has Kbb < 1 < 1 Leads to small [OHLeads to small [OH--] and a pH of 12 - 7 ] and a pH of 12 - 7
Model Weak Base
Equilibrium Constants for Acids/Bases Equilibrium Constants for Acids/Bases
AcidsAcids ConjugateConjugateBasesBases
Increase strength
Increase strength
pKa = -logKa pKb = -logKb pKw = pKa + pKb Kw = (Ka)(Kb) = 1014 (@25oC)
17.6 Know how to predict and calculate pH for three types of acid/base reactions:
1. Strong Acid/Strong Base 2. Weak Acid/Strong Base 3. Strong Acid/Weak Base
See Problem Solving Tip 17.
17.9 Define a Lewis Acid as electron pair donor Define a Lewis Base as an electron pair
acceptor
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Lewis acidLewis acid a substance that accepts an a substance that accepts an
electron pairelectron pair
Lewis Lewis basebase a substance that a substance that donates an electron pairdonates an electron pair
17.9
ACID-BASE THEORIES 2ACID-BASE THEORIES 2 of 2 of 2
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Many complex ions containing water undergo Many complex ions containing water undergo HYDROLYSISHYDROLYSIS to give acidic solutions. to give acidic solutions.
[Cu(H[Cu(H22O)O)44]]2+2+ + H + H22O O [Cu(H [Cu(H22O)O)33(OH)](OH)]++ + + HH33OO++
Lewis Acids & BasesLewis Acids & Bases
17.10 Use concept of molecular polarity to predict the strengths of acids
Why is CHWhy is CH33COCO22H an Acid?H an Acid?
1. The electronegativity of the O atoms causes the H 1. The electronegativity of the O atoms causes the H attached to O to be highly positive.attached to O to be highly positive.
2. The O—H bond is highly polar.2. The O—H bond is highly polar.3. The H atom of O—H is readily attracted to polar 3. The H atom of O—H is readily attracted to polar
HH22O. O.
–0.32
+0.24
+0.12
See Figure 17.12
• Trichloroacetic acid is a much stronger acid owing to Trichloroacetic acid is a much stronger acid owing to the high electronegativity of Cl.the high electronegativity of Cl.
• Cl withdraws electrons from the rest of the molecule. Cl withdraws electrons from the rest of the molecule. • This makes the O—H bond highly polar. The H of O—This makes the O—H bond highly polar. The H of O—
H is very positive.H is very positive.
Acetic acidAcetic acid Trichloroacetic acidTrichloroacetic acid
KKaa = 1.8 x 10 = 1.8 x 10-5-5 KKaa = 0.3 = 0.3