Acids and Bases Dr. Ron Rusay Spring 2004 © Copyright 2001-2004 R.J. Rusay

Acids and BasesAcids and Bases

Dr. Ron RusayDr. Ron Rusay

Spring 2004Spring 2004

© Copyright 2001-2004 R.J. Rusay© Copyright 2001-2004 R.J. Rusay

Introduction to AqueousIntroduction to Aqueous Acids & Bases Acids & Bases

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

Bases: taste bitter, feel soapy and Bases: taste bitter, feel soapy and cause certain dyes to turn color.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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Solution Test ApparatusSolution Test Apparatusfor Electrolytes for Electrolytes

04_43 Power Source

(a)(b)(c)+−+++−−−− −++

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

compounds are strong electrolytes.compounds are strong electrolytes. Most Most molecular compoundsmolecular compounds are non-conductors. 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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0.00mol 0.10mol 0.10mol

Strong vs. Weak ElectrolytesStrong vs. Weak Electrolytes

Sugar is non-ionized in water and does not conduct. Sugar is non-ionized in water and does not conduct.

What is an acid and how strong is it?What is an acid and how strong is it?

Acids have a proton, Acids have a proton, H+, eg HCl(aq).eg HCl(aq). A strong acid is 100% ionized. For example nitric A strong acid is 100% ionized. For example nitric

acid, acid, HNOHNO3 3 , produces 100% H+ (aq). Other common . Other common

strong acids are sulfuric, Hstrong acids are sulfuric, H22SOSO44 (aq) and (aq) and

hydrochloric, HCl (aq) which also produce hydrochloric, HCl (aq) which also produce 100% H+ (aq). .

Acids & Strong Acids:Acids & Strong Acids:

Dissociation Dissociation of Strong and of Strong and Weak AcidsWeak Acids

A weak acid does A weak acid does not dissociate not dissociate

100%, eg. Acetic 100%, eg. Acetic acid in vinegar.acid in vinegar.

Acid StrengthAcid Strength(continued)(continued)

A weak acid is not 100% ionized. For A weak acid is not 100% ionized. For example acetic acid, example acetic acid, CHCH33COOH,COOH,

produces <100% H+ (aq). Most acids, . Most acids, particularly organic acids, are weak particularly organic acids, are weak acids.acids.

Weak AcidsWeak Acids::

Strong or weak acids? Strong or weak acids?

Strong or weak acids? Strong or weak acids?

A scale to relate acidities. A scale to relate acidities.

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 group IA & IIA metal The common bases are group IA & IIA 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 (or reaction with water), eg. methyl amine has <100% hydroxide with water), eg. methyl amine has <100% hydroxide ion in aqueous solution.ion in aqueous solution.

HH33CNHCNH22(aq) + H(aq) + H22O(l) O(l) H H33CNHCNH33++(aq) + OH(aq) + OH(aq)(aq)

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

Strong or weak bases? Strong or weak bases?

Water as an Acid and a BaseWater as an Acid and a Base

Water is Water is amphotericamphoteric (it can behave (it can behave either as an acid or a base).either as an acid or a base).

HH22O + HO + H22O O H H33OO++ + OH + OH

conj conjconj conj acid 1 base 1 acid 2 base 2acid 1 base 1 acid 2 base 2

KKww = 1 = 1 10 101414 at 25°C at 25°C

Water: Self-ionizationWater: Self-ionization

The pH ScaleThe pH Scale pH pH log[Hlog[H++] ] log[Hlog[H33OO++] ]

pH in water ranges from 0 to 14.pH in water ranges from 0 to 14.

KKww = 1.00 = 1.00 10 101414 = [H = [H++] [OH] [OH]]

pKpKww = = 14.00 = pH + pOH14.00 = pH + pOH As pH rises, pOH falls (sum = 14.00).As pH rises, pOH falls (sum = 14.00).There are no theoretical limits on the values of pH or pOH. (e.g. pH of 2.0 M HCl is -0.301, the pH at Iron Mountain is ~ -2 to -3)

The pH of Some Familiar

Aqueous Solutions

[H3O+]

[OH-]

[OH-] = KW

[H3O+]

neutralsolution

acidicsolution

basicsolution

[H3O+]> [OH-]

[H3O+]< [OH-]

[H3O+] = [OH-]

Natural IndicatorsNatural Indicators

The pH ScaleThe pH Scale

1 1

1 1

1.0 1.0

12.0 12.0

1 x 101 x 10-11-11 3 3

1 x 101 x 10-4-44 4

1 x 101 x 10-1-1

Neutralization ReactionsNeutralization Reactions

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) _______________________________________________________


H+(aq) + OH -

(aq) ---> H2O(l)

Acid-Base TitrationAcid-Base Titration

Acid-Base TitrationAcid-Base Titration

Stomach ChemistryStomach Chemistry

BuffersBuffers

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Acids and Bases Dr. Ron Rusay Spring 2004 © Copyright 2001-2004 R.J. Rusay