Acids and Bases IAcids and Bases I

Dr. Ron RusayDr. Ron Rusay

Summer 2004Summer 2004

© Copyright 2004 R.J. Rusay© Copyright 2004 R.J. Rusay

Introduction to Aqueous AcidsIntroduction to Aqueous Acids

Acids: taste sour and cause certain dyes Acids: taste sour and cause certain dyes to change color.to change color.

Introduction to Aqueous BasesIntroduction to Aqueous Bases

Bases: taste bitter, feel soapy and cause certain dyes to turn color.Bases: taste bitter, feel soapy and cause certain dyes to turn color.

ElectrolytesElectrolytes Aqueous solutions can be categorized into 3 Aqueous solutions can be categorized into 3

types: non-electrolytes, strong electrolytes or types: non-electrolytes, strong electrolytes or weak electrolytes based on their ability to conduct weak electrolytes based on their ability to conduct electricity.electricity.

A solution must have A solution must have ions ions to conduct.to conduct. Pure Water Pure Water does not conduct.does not conduct. Aqueous solutions can be tested for conductivity Aqueous solutions can be tested for conductivity

which will determine the degree of ionization of which will determine the degree of ionization of the solutes.the solutes.

It is possible to have full or partial ionization.It is possible to have full or partial ionization.

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© Copyright 1995-2004 R.J. Rusay© Copyright 1995-2004 R.J. Rusay

Solution Test ApparatusSolution Test Apparatusfor Electrolytes for Electrolytes

04_43 Power Source

(a)(b)(c)+−+++−−−− −++

ConductivityConductivity

Electrolytes / IonizationElectrolytes / Ionization

ElectrolytesElectrolytes Almost all ionic compounds and a few molecular Almost all ionic compounds and a few molecular

compounds are strong electrolytes.compounds are strong electrolytes. Several molecular compounds are weak conductors, Several molecular compounds are weak conductors,

most are non-conductors.most are non-conductors. Conductivity is directly related to the amount of Conductivity is directly related to the amount of

ionization, i.e. ions in solution. Table salt, sodium ionization, i.e. ions in solution. Table salt, sodium chloride, is completely ionized:chloride, is completely ionized:

NaCl(s) + H2O(l) ---> NaCl(aq) ---> 0.10mol Na

+(aq) + Cl -

(aq)

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© Copyright 1995-2004 R.J. Rusay© Copyright 1995-2004 R.J. Rusay

Strong vs. Weak ElectrolytesStrong vs. Weak Electrolytes

Models of Acids and BasesModels of Acids and Bases

Arrhenius ConceptArrhenius Concept: Acids produce H: Acids produce H++ in in solution, bases produce OHsolution, bases produce OH ion. ion. Brønsted-LowryBrønsted-Lowry: Acids are H: Acids are H++ donors, donors, bases are proton acceptors.bases are proton acceptors.

HCl + HHCl + H22O O Cl Cl + H + H33OO++

Lewis Acids and BasesLewis Acids and Bases

Lewis AcidLewis Acid: electron pair : electron pair acceptoracceptor Lewis BaseLewis Base: electron pair : electron pair donordonorAl3+ + 6HOHAlOHH63+

Conjugate Acid/Base PairsConjugate Acid/Base Pairs

HA(aq) + HHA(aq) + H22O(l) O(l) H H33OO++(aq) + A(aq) + A(aq)(aq) conj conjconj conj

conjugate baseconjugate base: everything that remains : everything that remains of the acid molecule after a proton is lost.of the acid molecule after a proton is lost. conjugate acidconjugate acid: formed when the proton : formed when the proton is transferred to the base.is transferred to the base.

Conjugate Acid/Base PairsConjugate Acid/Base Pairs

conjugate baseconjugate base: everything that remains of the acid : everything that remains of the acid molecule after a proton is lost.molecule after a proton is lost.conjugate acidconjugate acid: formed when the proton is transferred : formed when the proton is transferred to the base.to the base.

Acid StrengthAcid Strength

100% of the acid is ionized. For example nitric acid, 100% of the acid is ionized. For example nitric acid, HNOHNO3 3 , produces 100% H+ (aq). Other common . Other common

strong acids are _______ and ___________.strong acids are _______ and ___________. Stong acids produce very weak Stong acids produce very weak

_________________, eg. _________________, eg. (NO(NO33))

Strong Acids:Strong Acids:

Structure and Acid StrengthStructure and Acid Strength

Bond polarity & bond strength affects acidity. In Bond polarity & bond strength affects acidity. In binary compounds:binary compounds:

Bond Polarity Bond Polarity (The higher the bond polarity, the (The higher the bond polarity, the stronger the bond, the weaker the acid) eg. ____stronger the bond, the weaker the acid) eg. ____

Bond Strength Bond Strength (The lower the bond strength, the (The lower the bond strength, the higher the resulting Hhigher the resulting H++ ionization and the ionization and the stronger the acid. ) eg. ____stronger the acid. ) eg. ____

Dissociation Dissociation of Strong and of Strong and Weak AcidsWeak Acids

Acid StrengthAcid Strength(continued)(continued)

A weak acid is not 100% ionized. For example A weak acid is not 100% ionized. For example acetic acid, acetic acid, CHCH33COOH,COOH, produces <100% H+ (aq). Most acids, particularly organic acids, are . Most acids, particularly organic acids, are weak acids.weak acids.

Weak acids produce a much stronger conjugate Weak acids produce a much stronger conjugate base than water, eg. The acetate ion: base than water, eg. The acetate ion: (CH(CH33COOCOO))

Weak AcidsWeak Acids::

Multiprotic AcidsMultiprotic Acids Monoprotic acids have 1 acidic H, Monoprotic acids have 1 acidic H,

diprotic have 2, eg. Sulfuric acid diprotic have 2, eg. Sulfuric acid HH22SOSO44 etc. etc.

In a strong multiprotic acid, like In a strong multiprotic acid, like HH22SOSO44, only the first H is strong; , only the first H is strong;

transferring the second H is transferring the second H is usually weakusually weakHH22SOSO44 + H + H22O O H H33OO+1+1 + + HSOHSO44

-1-1

HSOHSO44-1-1 + H + H22O O H H33OO+1+1 + SO + SO44

-2-2

Aqueous BasesAqueous Bases Any compound that accepts a proton is a base.Any compound that accepts a proton is a base. The common bases are __________ metal The common bases are __________ metal

hydroxide compounds. “hydroxide compounds. “StrongStrong” and “” and “weakweak” are ” are used in the same sense for bases as for acids.used in the same sense for bases as for acids.

StrongStrong = = complete dissociation complete dissociation (100% (100% hydroxide ion is supplied to the solution) An hydroxide ion is supplied to the solution) An example of a weak base is ammonia.example of a weak base is ammonia.

NH3 (g) + H2O(l) NH3 (aq) NH4+

(aq)+ OH-

(aq)

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⇔ ⇔

BasesBases(continued)(continued)

WeakWeak bases have very bases have very little dissociation little dissociation (or reaction with (or reaction with water), eg. methyl amine like ammonia has <100% water), eg. methyl amine like ammonia has <100% hydroxide ion in aqueous solution.hydroxide ion in aqueous solution.HH33CNHCNH22(aq) + H(aq) + H22O(l) O(l) H H33CNHCNH33

++(aq) + ____(aq)(aq) + ____(aq) Organic bases are weak bases; for example, dopamine Organic bases are weak bases; for example, dopamine (neurotransmitter), cadaverine (product of cellular (neurotransmitter), cadaverine (product of cellular decomposition), morphine (narcotic pain killer) and decomposition), morphine (narcotic pain killer) and cocaine are weak bases.cocaine are weak bases.

Natural IndicatorsNatural Indicators

Reactions of Acids & BasesReactions of Acids & Bases

• A use for natural indicators: “Neutralization Reactions”• Titrations• Constipation?

Neutralization ReactionsNeutralization Reactions

How would indicator be used?How would indicator be used?

Aqueous Reactions:Aqueous Reactions: NeutralizationNeutralization Net Ionic EquationsNet Ionic Equations

HCl(aq) + NaOH (aq) ---> NaCl (aq) + H2O(l) ___________________________________________________

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

(aq)

NaOH (aq) ---> Na+(aq)+ OH-

(aq)

NaCl (aq) ---> Na+(aq)+ Cl-

(aq) ________________________________________________

Na+(aq)+ OH-

(aq) + H+(aq) + Cl -

(aq) ---> Na+(aq)+

Cl-(aq) + H2O(l) _______________________________________________________

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H+(aq) + OH -

(aq) ---> H2O(l)

Stomach ChemistryStomach Chemistry

Acid-Base TitrationAcid-Base Titration

•Acids have pH < 7, Bases > 7, and 7 is neutralAcids have pH < 7, Bases > 7, and 7 is neutral•Without a pH meter how can the progress of Without a pH meter how can the progress of

reaction be monitored?reaction be monitored?

Acid-Base TitrationAcid-Base Titration

http://www.dartmouth.edu/~chemlab/techniques/titration.htmlhttp://chemistry.fullerton.edu/~chemdev/director/titrate.html

pH & Water