acids and bases. section 19.1 acid-base theories objectives: –define the properties of acids and...
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Section 19.1Acid-Base Theories
• OBJECTIVES:
–Compare and contrast acids and bases as defined by the theories of: a) Arrhenius, b) Brønsted-Lowry, and c) Lewis.
Class question• Where can acids
be found?– Sodas– Stomach– Vinegar– Citrus fruits
• Where can bases be found?– Soap– Drano– Antacid tablets– Windex– detergent
Properties of Acids• Taste sour• React with bases • Litmus paper test – turn blue
litmus paper red• Electrolytic – conduct electricity
–Can be strong or weak electrolytes in aqueous solution
Properties of Acids• They have a pH of less than 7 (more
on this concept of pH in a later lesson)
• How do you know if a chemical is an acid?– It usually starts with Hydrogen.– HCl, H2SO4, HNO3, etc. (but not water!)
Acids Affect Indicators, by changing their color
Blue litmus paper turns red in contact with an acid (and red paper stays red).
Properties of Bases• Taste bitter• Feels slippery• React with acids• Litmus paper test – turn red litmus
paper blue• electrolytic
Bases Affect Indicators
Red litmus paper turns blue in contact with a base (and blue paper stays blue).
Phenolphthalein turns purple in a base.
Nomenclature of Acids• Acids are composed of a(n)
________________ followed by a(n) _______
Hydrogen ion (H+)
anion
Ex: H+ + Cl1-
H+ + SO42-
HCl
H2SO4
Binary AcidsH+ + anion
• H+ + anion with –ide ending acid name is __________________
HCl anion? _______
acid name ________________
Hydro _____ic acid
Hydrochloric acid
chloride
Binary Acids H+ + anion
• H+ + anion with –ide ending acid name is __________________
HF anion? _______
acid name ________________
Hydro _____ic acid
Hydrofluoric acid
fluoride
OxyacidsH+ + anion
• H+ + anion with –ate ending acid name is __________________
HNO3 anion? _______
acid name ________________
_____ic acid
nitric acid
nitrate
Oxyacids H+ + anion
• H+ + anion with –ate ending acid name is __________________
H2SO4 anion? _______
acid name ________________
_____ic acid
sulfuric acid
sulfate
Oxyacids H+ + anion
• H+ + anion with –ite ending acid name is __________________
HNO2 anion? _______
acid name ________________
_____ous acid
nitrous acid
nitrite
Oxyacids H+ + anion
• H+ + anion with –ite ending acid name is __________________
HClO2 anion? _______
acid name ________________
_____ous acid
chlorous acid
chlorite
Writing acid formulas• Hydrobromic acid
anion? ___________ formula ______• Acetic acid
anion? ___________ formula ______• Nitrous acid
anion? ___________ formula ______
HBr
HC2H3O2
HNO2
Bromide (Br1-)
acetate(C2H3O21-)
nitrite (NO21-)
Nomenclature of Bases• Bases are composed of a(n)
_______ followed by
a(n) ________________
cation
hydroxide (OH1-)
Writing Base Names• Rule: name the cation and add
“hydroxide”
• NaOH
• Mg(OH)2
• Fe(OH)3
sodium hydroxide
magnesium hydroxide
Iron (III) hydroxide
Memorize: NH3 = ammonia
Writing base formulas• potassium hydroxide
cation? ______ formula ______• Calcium hydroxide
cation? ______ formula ______• Aluminum hydroxide
cation? ______ formula ______
KOH
Ca(OH)2
Al(OH)3
K+
Ca2+
Al3+
Ions In Solution• Why are some solutions acidic,
basic, or neutral?
It depends on number of H+ and OH- ions present.
Ions In Solution• Acidic solution – contain more H+
ions than OH- ions
4000 H+ and 0 OH- is acidic1000 H+ and 500 OH- is acidic5 H+ and 3 OH- is acidic
Ions In Solution• Basic Solution – contain more OH-
ions than H+ ions
4000 OH- and 0 H+ is basic1000 OH- and 500 H+ is basic5 OH- and 3 H+ is basic
Ions In Solution• Neutral Solution – equal amounts
of H+ and OH- ions
4000 OH- and 4000 H+ is neutral1000 OH- and 1000 H+ is neutral5 OH- and 5 H+ is neutral
Self Ionization of Water• Proper ionization
H2O + H2O hydronium ion
O
H H
H
H
O
H H O
H H
O++
H3O+ + OH-
Svante Arrhenius• He was a Swedish chemist (1859-1927),
and a Nobel prize winner in chemistry (1903)
• one of the first chemists to explain the chemical theory of the behavior of acids and bases
• Dr. Hubert Alyea (professor emeritus at Princeton University) was the last graduate student of Arrhenius.
Arrhenius Model of Acids and Bases
• Arrhenius Acids– Defn: contain H+ and ionizes to form H+
– ExamplesHCl
HNO3
H+ + Cl-
H+ + NO3-
makes solutionACIDIC
Arrhenius Model of Acids and Bases
• Arrhenius Bases– Defn: – contain OH- and ionizes to produce OH- ions– Examples
NaOH
Ca(OH)2
Na+ + OH-
Ca2+ + 2 OH-
makessolutionBASIC
Flaw with Arrhenius model
• Not all bases contain hydroxide• Ex: ammonia (NH3) is basic
– According to Arrhenius, since ammonia can NOT produce OH- it is NOT a base
• Therefore a new type of acid/base must be determined
Lewis Acids and Bases
• Gilbert Lewis focused on the donation or acceptance of a pair of electrons during a reaction
• Most general of all 3 definitions; acids don’t even need hydrogen!
Lewis Model• Lewis acid
– an atom, ion, or molecule that accepts an electron pair to form a covalent bond
• Lewis base– An atom, ion, or molecule that donates
an electron pair to form a covalent bond
Lewis Model• Lewis acid-base reaction
– The formation of one or more covalent bonds between an electron-pair donor and an electron-pair acceptor
Example– AcidsAcids are electron pair acceptors. – BasesBases are electron pair donors.
Lewis base
Lewis acid
Bronsted-Lowry Model
• Bronsted-Lowry Acid– Defn: proton/H+ donor
• can give H+ to another species
• Bronsted-Lowry Base– Defn: proton/H+ acceptor
• can take H+ from another species
**Acids and bases always come in **Acids and bases always come in pairs.**pairs.**
Bronsted-Lowry Model• REMEMBER!!!! REMEMBER!!!!
acids donate, bases accept protons
Ashley does boys always
Bronsted-Lowry Model
• Examples
HCl + H2O Cl- + H3O+
What is happening here?
Acid (donate
s proton)
Base (accepts proton)
Which is the acid? base?
HCl is an acidHCl is an acid — — wwhen it dissolves in water, it gives it’s proton to water.
Water is a base—when the HCl gives up the proton, water accepts it to form the hydronium ion
Bronsted-Lowry Model• Examples
NH3 + H2O NH4+ + OH-
What is happening here?
Acid (donates proton)
Base (accepts proton)
Which is the acid? base?
Why Ammonia is a Base• Ammonia can be explained as a
base by using Brønsted-Lowry:
NH3(aq) + H2O(l) ↔ NH41+
(aq) + OH1-(aq)
Ammonia is the hydrogen ion acceptor (base), and water is the hydrogen ion donor (acid).
Conjugate Acid/Base Pairs
• Conjugate acid – new species produced when base gains H+ ion
• Conjugate base – new species produced when acid donates H+ ion
Thus, a conjugate acid-base Thus, a conjugate acid-base pair is related by the pair is related by the loss or loss or gaingain of a of a single hydrogen ionsingle hydrogen ion..
Conjugate Acid/Base Pairs
• general Bronsted-Lowry reaction
acid + base conj. acid + conj. base
conj. acid/base pair
conj. acid/base pair
Every acid has a conjugate base.Every base has a conjugate acid.
Conjugate Acid/Base Pairs
• Examples
HNO3 + H2O H3O+ + NO3-
What is the acid? base?
acid base What is the conjugate acid/base?
C.A. C.B.
conj. acid/base pair
conj. acid/base pair
Conjugate Acid/Base Pairs
• Examples
NH3 + H2O NH4+ + OH-
What is the acid? base?
acidbaseWhat is the conjugate acid/base?
C.B.C.A.
conj. acid/base pair
conj. acid/base pair
Conjugate acid-base pairs
• What is the conjugate base of:H2SO4 _________ H3O+ ________
• What is the conjugate acid of:HPO4
2- _________ OH1- ________
HSO41-
H2PO41-
H2O
H2O
How can H2O be both acid and base?
What is the conjugate base?
Acid Conjugate BaseH2SO4
HPO42-
NH41+
H3O1+
H2O
HSO41-
PO43-
NH3
H2O
OH-
How can H2O be both acid and base?
Amphoteric• Defn – substance that can act as
both acids and bases
HNO3 + H2O H3O+ + NO3-
NH3 + H2O NH4+ + OH-
base
acid
Water is amphoteric b/c it acts as a base in one reaction and acts as an acid in the second
Is H2O abase or acid?
Is H2O abase or acid?
Mono-, Di-, Triprotic Acids• Defns
– monoprotic (HA) – one ionizable protonex: HF, HCl, HBr (= normality is 1)
– diprotic (H2A) – two ionizable protons
ex: H2SO4, H2CO3 (= normality is 2)
– triprotic (H3A) – three ionizable protons ex: H3PO4, H3BO3 (= normality is 3)
Polyprotic Acid Ionization
• Always forms ONE H+
H3PO4
H2PO41-
HPO42-
H2PO41- + H+
HPO42- + H+
PO43- + H+
Strength of Acids and Bases
• Acid/base strength is based on the degree to which they ionize
1) strong ()
2) weak ()
Strong Acid/Base• Defn – acid or base that
completely ionizes
HA H+ + A-
XOH X+ + OH-
100%
ionization
every single HA molecule ionizes into H+ and A-
100%
ionization
Strength• Strong Acid/BaseStrong Acid/Base
– 100% ionized in water– strong electrolyte
- +
HCl
HNO3
H2SO4
HBr
HI
HClO4
NaOH
KOH
Ca(OH)2
Ba(OH)2
6 Strong Acids• HCl – hydrochloric acid• HBr – hydrobromic acid• HI – hydroiodic acid
• HClO4 – perchloric acid
• H2SO4 – sulfuric acid
• HNO3 – nitric acid
Strong Bases• Group I and II metal hydroxides
LiOH
NaOH
KOH
RbOH
Mg(OH)2
Ca(OH)2
Sr(OH)2
Ba(OH)2
No need tomemorizeexact ones
Weak Acid/Base• Defn – acid or base that partially
ionizes
HA H+ + A-
XOH X+ + OH-
partial
ionization
not all will ionize; the weaker it isthe less it ionizes
Strength
• Weak Acid/BaseWeak Acid/Base– does not ionize completely– weak electrolyte– Dissociates into both ions and molecules
- +
HF
CH3COOH
H3PO4
H2CO3
HCN
NH3
Strong or weak, concentrated or diluted• For acids and bases, it is important
to distinguish between concentrated and dilute from strong and weak. The words _________ and __________have different meanings. Similarly, ___________ and ___________ are not the same either.
strong
weak
concentrated
dilute
Strong or weak, concentrated or diluted• Strong and weak refer to
____________________________
• Concentrated and dilute refer to____________________________
how much substance ionizes
how much solute is present
Example• 1 M HCl
• 12 M HCl
• 1 M H2CO3
• 12 M H2CO3
Strong and dilute
Strong and concentrated
weak and dilute
weak and concentrated
Ion Product Constant for Water (Kw)
• Defn: equilibrium value for self ionization of water (H2O H+ + OH-)
• Formula Kw = [H+][OH-] = 1 x 10-14
ALWAYSALWAYSALWAYS
Ion Product Constant for Water (Kw)
• in pure water [H+] = [OH-] = 1 x 10-7
• in non pure water (acidic/basic conditions), value of [H+] and [OH-] differ
Remember pure water is neutral
But still [H+][OH-] = 1 x 10-14
Is solution acidic, basic, or neutral?
• Acidic
• Basic
• neutral
[H+] > [OH-]
[H+] < [OH-]
[H+] = [OH-]
pH = -log[ H+]
The pH Scale
0
7INCREASING
ACIDITY NEUTRALINCREASING
BASICITY
14
pouvoir hydrogène (Fr.)“hydrogen power”
The pH Scale
pH of Common SubstancespH of Common SubstancespH of Common SubstancespH of Common Substances
pHc) change one pH unit
represents a ten fold change in strength- ex: pH = 3 vs pH = 4
pH 3 is 101 or 10 times more acidic- ex: pH = 7 vs pH = 10
pH 7 is 103 or 1000 times more acidic
The pH Scale
• What is the pH of 0.050 M HNO3?
pH = -log[H+]
pH = -log[0.050]
pH = 1.3
Acidic or basic?Acidic
Calculating [H+] and [OH-]
• Find the hydroxide ion concentration of 3.0 10-2 M HCl.
[H+][OH-] = 1.0 10-14
[3.0 10-2][OH-] = 1.0 10-14
[OH-] = 3.3 10-13 M
Acidic or basic?Acidic
• What is the molarity of HBr in a solution that has a pOH of 9.6?
pH + pOH = 14
pH + 9.6 = 14
pH = 4.4
Acidic
pH = -log[H+]
4.4 = -log[H+]
-4.4 = log[H+]
[H+] = 4.0 10-5 M HBr
Calculating [H+] and [OH-]Calculating [H+] and [OH-]
• A Ca(OH)2 solution has a pH of 8.0. Determine the [H+], [OH-], and [Ca(OH)2] for the solution.
pH = - log [H+]
log [H+] = -pH
[H+] = antilog (-pH) = antilog (-8.0) = 1 x 10-8 M H3O+
Calculating [H+] and [OH-]Calculating [H+] and [OH-]
Antilog is the same thing as 10^(x)
[H+] [OH-] = 1 x 10-14 M2
[OH-] = 1 x 10-14 M2 = 1 x 10-14 M2
[H+] 1 x 10-8 M
[OH-] = 1 x 10-6 M
Calculating [H+] and [OH-]Calculating [H+] and [OH-]
• Ca(OH)2 Ca2+ + 2OH-
( 1 x 10-6 M)
1 x 10-6 mol OH- 1 mol Ca(OH)2 = 5 x 10-7 mol/L Ca(OH)2
Liter 2 mol OH-
[Ca(OH)2] = 5 x 10-7 M
Calculating [H+] and [OH-]Calculating [H+] and [OH-]
Sample problem #1• Calculate the pH of a solution with
[H+] = 3.0 x 10-6 M.
pH = -log [H+] = - log [3.0 x 10-6]
= 5.52
Sample problem #2• Calculate the pH of a solution with [OH-] =
8.2 x 10-6.
pOH = -log[OH-]= -log [8.2 x 10-6]= 5.09
pH + pOH = 14pH + 5.09 = 14
pH = 8.91
[OH-] pOH pH
Sample problem #2• Calculate the pH of a solution with
[OH-] = 8.2 x 10-6.
[H+][OH-] = 1 x 10-14
[H+][8.2 x 10-6] = 1 x 10-14
[H+] = 1.22 x 10-9
pH = -log[1.22 x 10-9] = 8.91
[OH-] [H+] pH
Sample problem #3• What is the [H+] of a solution with
pH = 2?pH = -log[H+][H+] = 10-pH
= 10-2
= 0.01 M
Sample problem #4• (i) What is the [OH-] of a solution
with pOH = 3.7?
[OH-] = 10-pOH
[OH-] = 10-3.7
= 2 x 10-4 M
Sample problem #4
pH + pOH = 14pH + 3.7 = 14
pH = 10.3
•(ii) What is the pH and the [H+] if the pOH is 3.7?
pOH pH [H+]
[H+] = 10-pH
= 10-10.3
= 5 x 10-11 M
Reaction between acids and bases
• Neutralization (defn) – reaction of acid and base to form a salt and water– The reaction is a double replacement
• Salt (defn) – ionic compound made of – cation from base and – anion from acid
Reaction between acids and bases
• Ex reaction
Mg(OH)2 + HCl MgCl2 + H2Obase acid salt water
Mg2+ + OH- H+ + Cl-Mg2+ - cation from base
Cl- - anion from acid
NeutralizationACID + BASE SALT + WATER
HCl + NaOH NaCl + H2O
HC2H3O2 + NaOH NaC2H3O2 + H2O
– Salts can be neutral, acidic, or basic.
– Neutralization does not mean pH = 7.
weak
strong strong
strong
neutral
basic
Ex problems• i) What is the salt formed from
sulfuric acid (H2SO4) and potassium hydroxide (KOH)?
base cation?acid anion?
K+
SO42-
What is salt? K2SO4
Ex problems• ii) What is the salt formed when
Al(OH)3 and HBr react?
base cation?acid anion?
Al3+
Br-
What is salt? AlBr3
Is salt solution acidic, basic, or neutral?
• a) strong acid + strong base
• b) strong acid + weak base
• c) weak acid + strong base
Neutral salt
acidic salt
basic salt
Ex problem• Determine if salt solution is
acidic, basic, or neutral.
a) LiBracid?base?
HBr
LiOH
(strong acid)(strong base)
Salt is ____________NEUTRAL
Li+ + Br-
Ex problem• Determine if salt solution is
acidic, basic, or neutral.
b) Fe(NO3)3
acid?base?
HNO3
Fe(OH)3
(strong acid)(weak base)
Salt is ____________ACIDIC
Fe3+ + NO3-
B. Titration• Titration
– Analytical method in which a standard solution is used to determine the concentration of an unknown solution.
standard solution
unknown solution
• Equivalence point (endpoint)– Point at which equal amounts
of H3O+ and OH- have been added.
– Determined by…• indicator color change
B. Titration
• dramatic change in pH
B. Titration
moles H3O+ = moles OH-
MV n = MV n
M: MolarityV: volumen: # of H+ ions in the acid
or OH- ions in the base