Acids and Bases. Acids & Bases The Bronsted-Lowry model defines an acid as a proton donor. A base is...

Acids and BasesAcids and Bases

Acids & BasesAcids & Bases

The Bronsted-Lowry model The Bronsted-Lowry model defines an acid as a defines an acid as a proton donorproton donor. A . A base is a base is a proton acceptorproton acceptor. Note that . Note that this definition is based on the this definition is based on the transfer of a proton from the acid to transfer of a proton from the acid to the base.the base.

NHNH33((aqaq) + H) + H33OO++((ll))


HH22O(O(ll) + HCl() + HCl(gg) ) H H33OO++((aqaq) + ) + ClCl1-1-((aqaq))

In this reaction, water accepts a In this reaction, water accepts a

proton from HCl. Water is a base, and proton from HCl. Water is a base, and

HCl is an acid.HCl is an acid.

HH22O(O(ll) + HCl() + HCl(gg) ) H H33OO++((aqaq) + Cl) + Cl1-1-((aqaq))protonproton proton protonacceptoracceptor donor donorB-L baseB-L base B-L acid B-L acid


Since this reaction goes to Since this reaction goes to completion (note the one-way completion (note the one-way arrow), we classify HCl(aq) as a arrow), we classify HCl(aq) as a strongstrong acid. acid.

HH22O(O(ll) + HCl() + HCl(gg) ) H H33OO++((aqaq) + Cl) + Cl1-1-

((aqaq))protonproton proton protonacceptoracceptor donor donor


Hydrochloric acid Hydrochloric acid dissociatesdissociates 100%, and exists as a solution of 100%, and exists as a solution of hydronium and chloride ions.hydronium and chloride ions.

HH22O(O(ll) + HCl() + HCl(gg) ) H H33OO++((aqaq) + Cl) + Cl1-1-((aqaq))protonproton proton protonacceptoracceptor donor donor

Although a bottle may be labeled Although a bottle may be labeled 1.0M HCl, it really contains 1.0 M H1.0M HCl, it really contains 1.0 M H33OO++

((aqaq) and 1.0 M Cl) and 1.0 M Cl1-1-((aqaq).).


Hydrochloric acid Hydrochloric acid dissociatesdissociates 100%, and exists as a solution of 100%, and exists as a solution of hydronium and chloride ions.hydronium and chloride ions.

HH22O(O(ll) + HCl() + HCl(gg) ) H H33OO++((aqaq) + Cl) + Cl1-1-((aqaq))protonproton proton protonacceptoracceptor donor donor

There is There is no reverse reactionno reverse reaction because chloride has no tendency to because chloride has no tendency to accept a proton to form HCl.accept a proton to form HCl.


There are only a few common There are only a few common strong acids. They are:strong acids. They are:

HCl(HCl(aqaq), HNO), HNO33((aqaq), HClO), HClO44((aqaq) and ) and HH22SOSO44((aqaq)*)*

*for the first proton only*for the first proton only


Most acids are Most acids are weak acidsweak acids in which in which only a small percentage of the molecules only a small percentage of the molecules dissociate to protonate water.dissociate to protonate water.

HA(HA(aqaq) + H) + H22O(O(aqaq) ↔ H) ↔ H33OO++((aqaq) + A) + A--((aqaq))

HA is a generic monoprotic weak HA is a generic monoprotic weak acid such as HF, HCN or CHacid such as HF, HCN or CH33COOH.COOH.

Weak AcidsWeak Acids

Weak acids in water form an Weak acids in water form an equilibrium with hydronium ion and the equilibrium with hydronium ion and the deprotonated anion of the acid. The deprotonated anion of the acid. The reaction reaction does notdoes not go to completion. go to completion.

H-A + HH-A + H22O ↔ HO ↔ H33OO++ + +

AA--

AcidsAcidsThe equilibrium of acids in water can The equilibrium of acids in water can

be viewed as a competition between the be viewed as a competition between the forward reaction and the reverse reaction.forward reaction and the reverse reaction.

H-A + HH-A + H22O ↔ HO ↔ H33OO++ + A+ A--

AcidsAcids

The forward reaction involves HA, a The forward reaction involves HA, a generic acid, and water. Water acts as a generic acid, and water. Water acts as a base by accepting a proton from the acid.base by accepting a proton from the acid.

H-A + HH-A + H22O ↔ HO ↔ H33OO++ + A+ A--

AcidsAcids

The forward reaction involves The forward reaction involves HA, a generic acid, and water. HA, a generic acid, and water. Water acts as a base by accepting a Water acts as a base by accepting a proton from the acid.proton from the acid.

Acid HAproton donor

Base H2Oproton acceptor

H-A + HH-A + H22O ↔ HO ↔ H33OO++ + + A- A-

AcidsAcids

The reverse reaction involves AThe reverse reaction involves A-- accepting a proton and acting as a accepting a proton and acting as a base. Hbase. H33OO++ donates a proton, and is donates a proton, and is an acid. an acid. Acid HA

proton donor


Acid H3O+

proton donor

Base A-

proton acceptor

H-A + HH-A + H22O ↔ HO ↔ H33OO++ + + A A--

Conjugate Acids & BasesConjugate Acids & Bases

The deprotonated acid is a base, The deprotonated acid is a base, and the protonated base is an acid. and the protonated base is an acid. These acids and bases are called These acids and bases are called conjugate acids and basesconjugate acids and bases..

Acid HAproton donor


Acid H3O+

proton donor

Base A-

proton acceptor

H-A + HH-A + H22O ↔ HO ↔ H33OO++ + + A A--

AcidsAcidsFor weak acids, the equilibrium For weak acids, the equilibrium

lies to the left, indicating that Alies to the left, indicating that A-- is a is a stronger base than water. stronger base than water.

Acid HAproton donor


Acid H3O+

proton donor

Base A-

proton acceptor

AcidsAcids

Acid HA Base H2O Acid H3O+ Base A-

Acid HA and base A- are related, and differ only by the addition or removal of H+.

remove H+

add H+

AcidsAcids


HA and A- are called conjugate acid-base pairs. A- is the conjugate base of the acid HA.

remove H+

add H+

AcidsAcids


Likewise, H2O and H3O+ are related, and differ only by the addition or removal of H+.

remove H+

add H+

AcidsAcids


H2O and H3O+ are conjugate acid-base pairs. H2O is the conjugate base of H3O+ .

remove H+

add H+

Strong and Weak AcidsStrong and Weak Acids

HX is a weak acid and forms only a small amount of H3O+ and X-


HY is a strong acid and dissociates completely to form H3O+ and Y-

Acid StrengthAcid Strength

The conjugate bases of strong acids The conjugate bases of strong acids have have no tendencyno tendency to pick up a to pick up a proton. There is no reverse proton. There is no reverse reaction.reaction.

The conjugate bases of infinitely The conjugate bases of infinitely strong acids are infinitely weak.strong acids are infinitely weak.

Conjugate Conjugate Acid-Base Acid-Base StrengthStrength

The weaker the The weaker the acid, the stronger acid, the stronger its conjugate base. its conjugate base.

As the acid gets As the acid gets weaker, the reverse weaker, the reverse reaction with water reaction with water becomes more becomes more significant.significant.

Conjugate Acid-Base Conjugate Acid-Base StrengthStrength

KKaa Values Values

Acid strength is determined by Acid strength is determined by measuring the equilibrium constant measuring the equilibrium constant for the following reaction:for the following reaction:

HA(HA(aqaq) + H) + H22O(O(ll) ↔ H) ↔ H33OO++((aqaq) + A) + A--((aqaq))

KKaa = = [H[H33OO++][A][A--]] [HA][HA]

KKaa Values Values

HA(HA(aqaq) + H) + H22O(O(ll) ↔ H) ↔ H33OO++((aqaq) + ) + AA--((aqaq))

KKaa = = [H[H33OO++][A][A--]] [HA][HA]

Water is left out of the equilibrium Water is left out of the equilibrium constant expression because it is a pure constant expression because it is a pure liquid (with constant concentration). liquid (with constant concentration). The “The “aa” subscript stands for acid.” subscript stands for acid.

KKaa Values Values

Sulfuric AcidSulfuric Acid

Sulfuric acid, HSulfuric acid, H22SOSO44, can lose two , can lose two protons. It is called a protons. It is called a diprotic aciddiprotic acid. . Sulfuric acid is also one of the common Sulfuric acid is also one of the common strong acids. This applies to loss of the strong acids. This applies to loss of the first proton only.first proton only.

HH22SOSO44((aqaq) + H) + H22O(O(ll) ) H H33OO++((aqaq) + HSO) + HSO44--

((aqaq) )

This reaction goes 100% to the right.This reaction goes 100% to the right.


Sulfuric acid, HSulfuric acid, H22SOSO44, can lose two , can lose two protons. It is called a protons. It is called a diprotic aciddiprotic acid. . Sulfuric acid is also one of the common Sulfuric acid is also one of the common strong acids. This applies to loss of the strong acids. This applies to loss of the first proton only.first proton only.

HH22SOSO44((aqaq) + H) + H22O(O(ll) ) H H33OO++((aqaq) + HSO) + HSO44--((aqaq) )

HSOHSO44- - can react with water to lose an can react with water to lose an

additional proton.additional proton.


HSOHSO44--((aqaq) + H) + H22O(O(ll) ↔ H) ↔ H33OO++((aqaq) + SO) + SO44

2-2-

((aqaq))

The double arrows indicate an The double arrows indicate an equilibrium is established because HSOequilibrium is established because HSO44

-- is a weak acid.is a weak acid.

KKaa for HSO for HSO44- - = = [H[H33OO++][SO][SO44

2-2-]] = 1.2 x 10 = 1.2 x 10-2-2

[HSO[HSO44--]]


HSOHSO44--((aqaq) + H) + H22O(O(ll) ↔ H) ↔ H33OO++((aqaq) + SO) + SO44

2-2-((aqaq))

KKaa for HSO for HSO44- - = = [H[H33OO++][SO][SO44

2-2-]] = 1.2 x 10 = 1.2 x 10-2-2

[HSO[HSO44--]]

The value of KThe value of Kaa indicates that indicates that hydrogen sulfate ion is a relatively strong hydrogen sulfate ion is a relatively strong weak acid. It is stronger than most weak weak acid. It is stronger than most weak acids, but weaker than the strong acids acids, but weaker than the strong acids HCl, HNOHCl, HNO33, H, H22SOSO44 or HClO or HClO44..

KKaa Values Values

BasesBases

Strong bases are very effective at Strong bases are very effective at accepting protons. The most common accepting protons. The most common strong bases are the soluble group IA and strong bases are the soluble group IA and IIA metal hydroxides. IIA metal hydroxides. In general, the In general, the metal ion is non-reactive, and serves as a metal ion is non-reactive, and serves as a spectator ion.spectator ion.

Another strong base is oxide ion, OAnother strong base is oxide ion, O2-2-. . Oxide reacts with water to become fully Oxide reacts with water to become fully protonated.protonated.

OO2-2-((aqaq) + H) + H22O(O(ll) ) 2 OH 2 OH--((aqaq))

BasesBases

OO2-2-((aqaq) + H) + H22O(O(ll) ) 2 OH 2 OH--((aqaq))

In this reaction, water is In this reaction, water is donating a proton, and hence acting donating a proton, and hence acting as an acid. In previous reactions, as an acid. In previous reactions, water accepted a proton and served water accepted a proton and served as a base. Substances that can as a base. Substances that can behave as either an acid or a base are behave as either an acid or a base are called called amphotericamphoteric..

Amphoteric Nature of Amphoteric Nature of WaterWater

Depending upon its environment, Depending upon its environment, water may donate a proton, acting as water may donate a proton, acting as an acid, or accept a proton, and act as an acid, or accept a proton, and act as a base. This behavior is characteristic a base. This behavior is characteristic of of amphotericamphoteric substances. substances.

Pure water molecules can react with Pure water molecules can react with each other, to a very small extent, to each other, to a very small extent, to form hydronium and hydroxide ions.form hydronium and hydroxide ions.

Autoionization of WaterAutoionization of Water

This process is called This process is called autoionization autoionization or or selfionization. selfionization. One One water molecule donates a proton to water molecule donates a proton to another. The result is the formation another. The result is the formation of equal amounts of hydronium and of equal amounts of hydronium and hydroxide ions.hydroxide ions.

HH22O(O(ll) + H) + H22O(O(ll) ↔ H) ↔ H33OO++((aqaq) + ) + OHOH--((aqaq))


HH22O(O(ll) + H) + H22O(O(ll) ↔ H) ↔ H33OO++((aqaq) + OH) + OH--((aqaq))

KKww = [H = [H33OO++][OH][OH--] = 1.0 x 10] = 1.0 x 10-14-14 at 25 at 25ooCC

In pure water, the concentration In pure water, the concentration of hydronium ion equals the of hydronium ion equals the concentration of hydroxide. Both ions concentration of hydroxide. Both ions have a concentration of 1.0 x 10have a concentration of 1.0 x 10-7-7M.M.

[H[H33OO++] and [OH] and [OH--] in ] in Aqueous SolutionAqueous Solution

The product of the hydroxide The product of the hydroxide and hydronium concentration in any and hydronium concentration in any aqueous solution must equal Kaqueous solution must equal Kww. .

As a result, when a solution is As a result, when a solution is acidic, the hydronium concentration acidic, the hydronium concentration increases, and the hydroxide increases, and the hydroxide concentration decreases.concentration decreases.


Likewise, in basic solutions, the Likewise, in basic solutions, the hydroxide ion concentration is hydroxide ion concentration is greater than the hydronium ion greater than the hydronium ion concentration. concentration.

There is There is alwaysalways some hydroxide some hydroxide ion and some hydronium ion present ion and some hydronium ion present in any aqueous solution.in any aqueous solution.

The pH ScaleThe pH Scale

A scale of acidity, the pH scale, is A scale of acidity, the pH scale, is used to indicate the degree of acidity used to indicate the degree of acidity of aqueous solutions. of aqueous solutions.

pH = -log[HpH = -log[H33OO++] or –log[H] or –log[H++]]

The scale generally runs from 0-The scale generally runs from 0-14, though negative pH values are 14, though negative pH values are possible. A neutral solution will have possible. A neutral solution will have a pH = 7.00a pH = 7.00

The pH ScaleThe pH Scale

A one unit change in pH is a ten-A one unit change in pH is a ten-fold change in the concentration of fold change in the concentration of hydronium ion.hydronium ion.

Acidic solutions have pH values Acidic solutions have pH values less than 7.00, and basic solutions less than 7.00, and basic solutions have pH values greater than 7.00have pH values greater than 7.00

pH ValuespH Values

Most foods Most foods have pH values in have pH values in the acidic range.the acidic range.

Problem: Calculation of Problem: Calculation of pHpH

Calculate the pH of 0.10M HCl.Calculate the pH of 0.10M HCl.- Is it an acid or a base?- Is it an acid or a base?- Is it strong or weak?- Is it strong or weak?- Write the appropriate chemical - Write the appropriate chemical reaction(s).reaction(s).

HCl(HCl(aqaq) + H) + H22O(O(ll) ) H H33OO++((aqaq) + Cl) + Cl--((aqaq))oror

HCl(HCl(aqaq) ) H H++(aq) + Cl(aq) + Cl--((aqaq))


Calculate the pH of 0.10M HCl.Calculate the pH of 0.10M HCl.

HCl(HCl(aqaq) + H) + H22O(O(ll) ) H H33OO++((aqaq) + Cl) + Cl--

((aqaq))

[H[H33OO++] = 0.10M] = 0.10M

pH = - log [HpH = - log [H33OO++] = - log( 0.10) = 1.00] = - log( 0.10) = 1.00

For every significant digit in the For every significant digit in the concentration, there is a place after the concentration, there is a place after the decimal in the pH.decimal in the pH.


Calculate the pH of 0.10M HCl.Calculate the pH of 0.10M HCl.

pH = - log [HpH = - log [H33OO++] = - log( 0.10) = 1.00] = - log( 0.10) = 1.00

- Does your answer make sense? - Does your answer make sense?

The pH of a fairly concentrated The pH of a fairly concentrated strong acid should be much less than strong acid should be much less than 7. Yes, the answer makes sense.7. Yes, the answer makes sense.

Question: pHQuestion: pH

Can you have a negative value for Can you have a negative value for pH? Under what circumstances?pH? Under what circumstances?

If the hydronium concentration If the hydronium concentration is > 1.0M, the pH will be negative. is > 1.0M, the pH will be negative. pH will be zero if the hydronium pH will be zero if the hydronium concentration equals 1.0M.concentration equals 1.0M.

Problem: pHProblem: pH

Calculate the pH of 1.5 x 10Calculate the pH of 1.5 x 10-10-10M M HClOHClO44..


Calculate the pH of 0.0050M Calculate the pH of 0.0050M Ca(OH)Ca(OH)22..

- Acid or base?- Acid or base?

- Strong or weak?- Strong or weak?

- Write the reaction(s).- Write the reaction(s).

Ca(OH)Ca(OH)22 in water is a strong in water is a strong base.base.

Ca(OH)Ca(OH)22((aqaq) ) Ca Ca2+2+((aqaq) + 2 OH) + 2 OH--((aqaq))


Calculate the pH of 0.0050M Ca(OH)Calculate the pH of 0.0050M Ca(OH)22..

Ca(OH)Ca(OH)22((aqaq) ) Ca Ca2+2+((aqaq) + 2 OH) + 2 OH--((aqaq)) 0.0050M0.0050M 0.0050M0.0050M

2(0.0050M)2(0.0050M)

[OH[OH--] = 2(0.0050M) = 0.0100M] = 2(0.0050M) = 0.0100M

Since [OHSince [OH--] and ] and [H3O+] are related by Kw, the pH can be calculated.

Problem: pH from [OHProblem: pH from [OH--]]

[OH[OH--] = 2(0.0050M) = 0.0100M] = 2(0.0050M) = 0.0100M

You can use: [HYou can use: [H33OO++] [OH] [OH--] = 1.0 ] = 1.0 x 10x 10-14-14 to calculate hydronium to calculate hydronium concentration and the pH, or:concentration and the pH, or:

pH + pOH = -log KpH + pOH = -log Kww=14.00 (=14.00 (@@2525ooC)C)

Problem: pH of 0.50M Problem: pH of 0.50M HCNHCN

Calculate the pH of 0.50M HCN. (KCalculate the pH of 0.50M HCN. (Kaa

= 6.2 x 10= 6.2 x 10-10-10.).)

Problem: pH of 0.50M Problem: pH of 0.50M HCNHCN

-- State any assumptions. State any assumptions.- Solve the problem.Solve the problem.- Check your assumptions.Check your assumptions.- Answer the question.Answer the question.- Does your answer make sense?Does your answer make sense?- Check your results, if possible.Check your results, if possible.

pH of Weak AcidspH of Weak Acids

If the same question were asked If the same question were asked concerning a 0.50 M solution of chlorous concerning a 0.50 M solution of chlorous acid, HClOacid, HClO22 (K (Kaa=1.2 x 10=1.2 x 10-2-2), you would ), you would need to use the quadratic formula to need to use the quadratic formula to answer the question.answer the question.

Generally, if the acid concentration Generally, if the acid concentration is .10M or larger, and K is 10is .10M or larger, and K is 10-5-5 or or smaller, you won’t need to use the smaller, you won’t need to use the quadratic formula.quadratic formula.

Problem: What is the pH of Problem: What is the pH of 0.15M NH0.15M NH33??

NHNH33 is a weak base, and NH is a weak base, and NH44++ is its is its

conjugate acid.conjugate acid.

Kb = [OH-][NH4+]

[NH3]

Values of Kb for Some Values of Kb for Some Common Weak BasesCommon Weak Bases

Polyprotic AcidsPolyprotic Acids

Acids that have more than one Acids that have more than one proton than can be donated are proton than can be donated are called called polyproticpolyprotic acids. Examples acids. Examples are Hare H22SOSO44, H, H33POPO44, H, H22S and HS and H22COCO33. .

The loss of protons can be The loss of protons can be viewed as a step-wise process. viewed as a step-wise process.


HH33A(A(aqaq) + H) + H22O(O(ll) ↔ H) ↔ H33OO++((aqaq) + H) + H22AA--

((aqaq))

KKa1a1 = [H = [H33OO++][H][H22AA--]/[H]/[H33A]A]

HH22AA--((aqaq) + H) + H22O(O(ll) ↔ H) ↔ H33OO++((aqaq) + HA) + HA2-2-((aqaq))

KKa2a2 = [H = [H33OO++][HA][HA2-2-]/[H]/[H22AA--]]

HAHA2-2-((aqaq) + H) + H22O(O(ll) ↔ H) ↔ H33OO++((aqaq) + A) + A3-3-(aq)(aq)

KKa3a3 = [H = [H33OO++][A][A3-3-]/[HA]/[HA2-2-]]


For all polyprotic acids, For all polyprotic acids, KKa1a1>K>Ka2a2>K>Ka3a3. It becomes progressively . It becomes progressively more difficult to remove protons as the more difficult to remove protons as the acid becomes more negative in charge.acid becomes more negative in charge.

Since the first dissociation usually Since the first dissociation usually predominates, it can often be used to predominates, it can often be used to determine the pH of a solution of the determine the pH of a solution of the polyprotic acid. The subsequent steps polyprotic acid. The subsequent steps are usually negligible.are usually negligible.

Problem: Polyprotic Problem: Polyprotic AcidsAcids

Calculate the pH and the Calculate the pH and the concentration of all species present concentration of all species present in 0.40M Hin 0.40M H22COCO33. (K. (Ka1a1 = 4.3 x 10 = 4.3 x 10-7-7, , KKa2a2 =5.6 x 10 =5.6 x 10-11-11).).

Since KSince Ka1a1>>K>>Ka2a2, the pH can be , the pH can be obtained by considering only the obtained by considering only the first dissociation.first dissociation.

pH of Salt SolutionspH of Salt Solutions

When salts (ionic compounds) When salts (ionic compounds) dissolve in water, they dissociate dissolve in water, they dissociate into separate hydrated ions. Since into separate hydrated ions. Since many ions are conjugate acids or many ions are conjugate acids or bases, they may react to form bases, they may react to form hydronium or hydroxide ions.hydronium or hydroxide ions.


Since the conjugate bases of strong acids Since the conjugate bases of strong acids have no tendency to accept protons, have no tendency to accept protons, these ions will have no effect on pH.these ions will have no effect on pH.

The “neutral” anions are: ClThe “neutral” anions are: Cl --, Br, Br--, I, I--, NO, NO33--

and ClOand ClO44--

(Although HSO(Although HSO441-1- isn’t basic, isn’t basic, it is acidicit is acidic, ,

and will donate a proton to form and will donate a proton to form hydronium ion.)hydronium ion.)


The cations of strong bases also The cations of strong bases also have no effect on pH when dissolved have no effect on pH when dissolved in water. As a result, the group IA in water. As a result, the group IA and group IIA metal ions will and group IIA metal ions will produce neutral solutions.produce neutral solutions.

Some highly positively charged Some highly positively charged ions, such as Alions, such as Al3+ 3+ or Feor Fe3+3+ produce produce slightly acidic solutions.slightly acidic solutions.


Are the following aqueous solutions Are the following aqueous solutions acidic, basic or neutral?acidic, basic or neutral?

NaNONaNO33, KCN, NH, KCN, NH44Cl, Ca(HSOCl, Ca(HSO44))22, , LiCHLiCH33COCO22


Calculate the pH of 0.10M NaCHCalculate the pH of 0.10M NaCH33COCO22..

NaCHNaCH33COCO22((aqaq) ) Na Na++((aqaq) + CH) + CH33COCO22--((aqaq))

Acetate ion is the conjugate base of the Acetate ion is the conjugate base of the weak acid, acetic acid. So, acetate will act as weak acid, acetic acid. So, acetate will act as a base and accept protons from water.a base and accept protons from water.

CHCH33COCO22--((aqaq) + H) + H22O(O(aqaq) ↔ CH) ↔ CH33COCO22H(H(aqaq) + OH) + OH--

((aqaq))

The solution should be basic with the pH>7.0The solution should be basic with the pH>7.0


Calculate the pH of 0.10M NaCHCalculate the pH of 0.10M NaCH33COCO22..

CHCH33COCO22--((aqaq) + H) + H22O(O(aqaq) ↔ CH) ↔ CH33COCO22H(H(aqaq) + OH) + OH--((aqaq))

KKbb = = [CH [CH33COCO22H][OHH][OH--]][CH[CH33COCO22

--]]

The value of KThe value of Kb b for acetate ion can be for acetate ion can be calculated from the value of Kcalculated from the value of Kaa for acetic for acetic acid.acid.


For any weak conjugate acid-base pairs,For any weak conjugate acid-base pairs,

KKaa(K(Kbb) = K) = Kww

(K(Kaa for acetic acid) (K for acetic acid) (Kbb for acetate ion)= for acetate ion)=

1.0 x 101.0 x 10-14-14

KKbb for acetate ion=1.0 x 10 for acetate ion=1.0 x 10-14-14/1.8 x 10/1.8 x 10-5-5

= 5.6 x 10= 5.6 x 10-10-10

Structure and Acids & Structure and Acids & BasesBases

For binary acids of the general For binary acids of the general formula Hformula HnnX (where X is a non-X (where X is a non-metal), the acidity reflects the H-X metal), the acidity reflects the H-X bond strength and polarity. bond strength and polarity.

If the bond is strong and non-If the bond is strong and non-polar, such as with carbon (in CHpolar, such as with carbon (in CH44), ), the compound is non-acidic, and the the compound is non-acidic, and the C-H bonds remain intact.C-H bonds remain intact.


The effects of bond polarity can be The effects of bond polarity can be seen in the hydrogen halides: HF, HCl, seen in the hydrogen halides: HF, HCl, HBr and HI. HBr and HI.

HF has the most polar bond, yet it is HF has the most polar bond, yet it is the weakest acid of the group (Kthe weakest acid of the group (Kaa=7.2 x =7.2 x 1010-4-4). The HF bond is the strongest of ). The HF bond is the strongest of the group, and this very high bond the group, and this very high bond strength results in a lower tendency for strength results in a lower tendency for dissociation in water.dissociation in water.


The acids HCl, HBr and HI are The acids HCl, HBr and HI are all strong acids. In all cases, the all strong acids. In all cases, the bonds are polar, but they are also bonds are polar, but they are also weaker than the H-F bond, and are weaker than the H-F bond, and are more easily broken in aqueous more easily broken in aqueous solution.solution.

The OxyacidsThe Oxyacids

The oxyacids typically have one The oxyacids typically have one or more oxygen atoms attached to a or more oxygen atoms attached to a central non-metal. Attached to one central non-metal. Attached to one or more of the oxygen atoms are or more of the oxygen atoms are acidic hydrogens. Examples include acidic hydrogens. Examples include HH22SOSO44, HNO, HNO33, HNO, HNO22, H, H33POPO44 and and HClOHClO44. It is important to remember . It is important to remember that in all cases, the acidic hydrogen that in all cases, the acidic hydrogen is attached to is attached to oxygenoxygen (X-O-H). (X-O-H).

The OxyacidsThe Oxyacids

OxyacidsOxyacidsFor a given For a given

central atom, the central atom, the greater the greater the number of oxygen number of oxygen atoms attached, atoms attached, the more acidic the the more acidic the acid. The larger acid. The larger number of oxygen number of oxygen atoms polarizes atoms polarizes and weakens the and weakens the O-H bonds.O-H bonds.

OxyacidsOxyacids

The greater the number of oxygen atoms, the weaker the O-H bonds, and the stronger the acid.

OxyacidsOxyacids

The nature of the central atom The nature of the central atom also affects the acidity of the acid. also affects the acidity of the acid. The more electronegative X is (in X-The more electronegative X is (in X-O-H), the weaker the O-H bond, and O-H), the weaker the O-H bond, and the stronger the acid.the stronger the acid.

OxyacidsOxyacidsThe nature of the central atom also The nature of the central atom also

affects the acidity of the acid. The more affects the acidity of the acid. The more electronegative X is (in X-O-H), the electronegative X is (in X-O-H), the weaker the O-H bond, and the stronger weaker the O-H bond, and the stronger the acid.the acid.

Acids and Bases. Acids & Bases The Bronsted-Lowry model defines an acid as a proton donor. A base is...

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Transcript of Acids and Bases. Acids & Bases The Bronsted-Lowry model defines an acid as a proton donor. A base is...