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