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Acids andBases
Acids andBases
RNA uses amino-acids to build proteins/enzymes
It is the acids in citrus fruits that give them the sour taste
and allows the fruit to stay in a state of preservation till
germination
Digestive Acids help to break down food into reusable molecular fragments
2
Properties of Acids
sour taste react with active metals (Al, Zn, Fe), but not Cu, Ag, or Au
2 Al(s) + 6 HCl(aq) 2 AlCl3(aq) + 3 H2(g)
Corrosive
react with carbonates, producing CO2
marble, baking soda, chalk, limestoneCaCO3(s) + 2 HCl(aq) CaCl2(aq) + CO2(g) + H2O(l)
change color of vegetable dyes blue litmus turns red
react with bases to form ionic salts
HCl(aq) + NaOH(aq)NaCl(aq) + H2O(l)
3
Common Acids
4
binary acids have acid hydrogens attached to a nonmetal atom
HCl, HF
binary acids have acid hydrogens attached to a nonmetal atom
HCl, HF
Structure of AcidsStructure of Acids
5
Structure of AcidsStructure of Acids
oxy acids have acid hydrogens attached to an oxygen atom
H2SO4, HNO3
oxy acids have acid hydrogens attached to an oxygen atom
H2SO4, HNO3
6
Structure of AcidsStructure of Acids
carboxylic acids have COOH group
HC2H3O2, H3C6H5O7
only the first H in the formula is acidic
the H is on the COOH
carboxylic acids have COOH group
HC2H3O2, H3C6H5O7
only the first H in the formula is acidic
the H is on the COOH
7
Properties of Bases
also known as alkalis taste bitter
alkaloids = plant product that is alkaline often poisonous
solutions feel slippery change color of vegetable dyes
different color than acid red litmus turns blue
react with acids to form ionic salts Neutralization
HCl(aq) + NaOH(aq)NaCl(aq) + H2O(l)
8
Common Bases
9
Structure of BasesStructure of Bases
most ionic bases contain OH- ions NaOH, Ca(OH)2
some contain CO32- ions
CaCO3 NaHCO3
molecular bases contain structures that react with H+
mostly amine groups
most ionic bases contain OH- ions NaOH, Ca(OH)2
some contain CO32- ions
CaCO3 NaHCO3
molecular bases contain structures that react with H+
mostly amine groups
Amino acids have a base at one end and an acid at the other, neighboring amino acids can neutralize to
form a polypeptide
10
Indicators chemicals which change color depending on the acidity/basicity many vegetable dyes are indicators
anthocyanins litmus
from Spanish moss red in acid, blue in base
phenolphthalein found in laxatives red in base, colorless in acid
Anthocyanins give these pansies their dark purple pigmentation and are the pigment in red cabbage that is so sensitive to acidity
11
acids and bases: Arrhenius Theoryacids and bases: Arrhenius Theory
bases dissociate in water to produce OH- ions and cations ionic substances dissociate in water
NaOH(aq) → Na+(aq) + OH–(aq)
acids ionize in water to produce H+ ions and anions
HCl(aq) → H+(aq) + Cl–(aq)
HC2H3O2(aq) H+(aq) + C2H3O2–(aq)
bases dissociate in water to produce OH- ions and cations ionic substances dissociate in water
NaOH(aq) → Na+(aq) + OH–(aq)
acids ionize in water to produce H+ ions and anions
HCl(aq) → H+(aq) + Cl–(aq)
HC2H3O2(aq) H+(aq) + C2H3O2–(aq)
12
Arrhenius TheoryArrhenius Theory
HCl ionizes in waterproducing H+ and Cl– ions
NaOH dissociates in waterproducing Na+ and OH– ions
13
Hydronium IonHydronium Ion
the H+ ions produced by the acid are so reactive they cannot exist in water H+ ions are protons
instead, they react with a water molecule(s) to produce complex ions, mainly hydronium ion, H3O+
H+ + H2O H3O+ ≅ H+(aq)
there are also minor amounts of H+ with multiple water molecules, H(H2O)n
+
the H+ ions produced by the acid are so reactive they cannot exist in water H+ ions are protons
instead, they react with a water molecule(s) to produce complex ions, mainly hydronium ion, H3O+
H+ + H2O H3O+ ≅ H+(aq)
there are also minor amounts of H+ with multiple water molecules, H(H2O)n
+
14
Arrhenius Acid-Base ReactionsArrhenius Acid-Base Reactions
the H+ from the acid combines with the OH- from the base to make a molecule of H2O
it is often helpful to think of H2O as H-OH
the cation from the base combines with the anion from the acid to make a salt
acid + base → salt + water
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
H+(aq)+Cl-(aq)+Na+
(aq)+OH-(aq)Na+
(aq)+Cl-(aq)+H2O(l)
H+(aq) + OH-
(aq) H2O(l)
All acid base reactions have this same net ionic equation in the Arrhenius idea of the acid and base
the H+ from the acid combines with the OH- from the base to make a molecule of H2O
it is often helpful to think of H2O as H-OH
the cation from the base combines with the anion from the acid to make a salt
acid + base → salt + water
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
H+(aq)+Cl-(aq)+Na+
(aq)+OH-(aq)Na+
(aq)+Cl-(aq)+H2O(l)
H+(aq) + OH-
(aq) H2O(l)
All acid base reactions have this same net ionic equation in the Arrhenius idea of the acid and base
15
Limitations of the Arrhenius TheoryLimitations of the Arrhenius Theory
does not explain why molecular substances, like NH3, dissolve in water to form basic solutions – even though they do not contain OH– ions
does not explain how some ionic compounds, like Na2CO3 or Na2O, dissolve in water to form basic solutions – even though they do not contain OH– ions
does not explain why molecular substances, like CO2, dissolve in water to form acidic solutions – even though they do not contain H+ ions
does not explain acid-base reactions that take place outside aqueous solution
does not explain why molecular substances, like NH3, dissolve in water to form basic solutions – even though they do not contain OH– ions
does not explain how some ionic compounds, like Na2CO3 or Na2O, dissolve in water to form basic solutions – even though they do not contain OH– ions
does not explain why molecular substances, like CO2, dissolve in water to form acidic solutions – even though they do not contain H+ ions
does not explain acid-base reactions that take place outside aqueous solution
16
Acids and bases: Brønsted-Lowry
in a Brønsted-Lowry Acid-Base reaction, an H+ is transferred does not have to take place in aqueous solution broader definition than Arrhenius
An acid is H+ donor, base is H+ acceptor base structure must contain an atom with an unshared pair of
electrons
in an acid-base reaction, the acid molecule gives an H+ to the base molecule
H–A + :B :A– + H–B+
17
Brønsted-Lowry AcidsBrønsted-Lowry Acids
Brønsted-Lowry acids are H+ donors any material that has H can potentially be a Brønsted-Lowry acid because of the molecular structure, often one H in the molecule is easier
to transfer than others
HCl(aq) is acidic because HCl transfers an H+ to H2O, forming H3O+ ions water acts as base, accepting H+
Brønsted-Lowry acids are H+ donors any material that has H can potentially be a Brønsted-Lowry acid because of the molecular structure, often one H in the molecule is easier
to transfer than others
HCl(aq) is acidic because HCl transfers an H+ to H2O, forming H3O+ ions water acts as base, accepting H+
HCl(aq) + H2O(l) → Cl–(aq) + H3O+
(aq)Acid base
Tro, Chemistry: A Molecular Approach
18
Brønsted-Lowry BasesBrønsted-Lowry Bases
Brønsted-Lowry bases are H+ acceptors any material that has atoms with lone pairs can potentially be a Brønsted-
Lowry base because of the molecular structure, often one atom in the molecule is
more willing to accept H+ transfer than others
NH3(aq) is basic because NH3 accepts an H+ from H2O, forming OH–
(aq) water acts as acid, donating H+
Brønsted-Lowry bases are H+ acceptors any material that has atoms with lone pairs can potentially be a Brønsted-
Lowry base because of the molecular structure, often one atom in the molecule is
more willing to accept H+ transfer than others
NH3(aq) is basic because NH3 accepts an H+ from H2O, forming OH–
(aq) water acts as acid, donating H+
NH3(aq) + H2O(l) NH4+(aq) + OH–(aq)
base acid
19
Amphoteric SubstancesAmphoteric Substances
amphoteric substances can act as either an acid or a base have both transferable H and atom with lone pair
Example water acts as base, accepting H+ from HCl
HCl(aq) + H2O(l) → Cl–(aq) + H3O+(aq)
water acts as acid, donating H+ to NH3
NH3(aq) + H2O(l) → NH4+
(aq) + OH–(aq)
amphoteric substances can act as either an acid or a base have both transferable H and atom with lone pair
Example water acts as base, accepting H+ from HCl
HCl(aq) + H2O(l) → Cl–(aq) + H3O+(aq)
water acts as acid, donating H+ to NH3
NH3(aq) + H2O(l) → NH4+
(aq) + OH–(aq)
20
Brønsted-Lowry: Acid-Base ReactionsBrønsted-Lowry: Acid-Base Reactions
one of the advantages of Brønsted-Lowry theory is that it allows reactions to be reversible
H–A + :B :A– + H–B+
the original base has an extra H+ after the reaction – so it will act as an acid in the reverse process
and the original acid has a lone pair of electrons after the reaction – so it will act as a base in the reverse process
:A– + H–B+ H–A + :B
one of the advantages of Brønsted-Lowry theory is that it allows reactions to be reversible
H–A + :B :A– + H–B+
the original base has an extra H+ after the reaction – so it will act as an acid in the reverse process
and the original acid has a lone pair of electrons after the reaction – so it will act as a base in the reverse process
:A– + H–B+ H–A + :B
21
Conjugate PairsConjugate Pairs
In a Brønsted-Lowry Acid-Base reaction, the original base becomes an acid in the reverse reaction, and the original acid becomes a base in
the reverse process
each reactant and the product it becomes is called a conjugate pair
the original base becomes the conjugate acid; and the original acid becomes the conjugate base
NH3(aq) + H2O(l) NH4+
(aq) + OH–(aq)
Base Acid Conjugate Acid Conjugate Base
In a Brønsted-Lowry Acid-Base reaction, the original base becomes an acid in the reverse reaction, and the original acid becomes a base in
the reverse process
each reactant and the product it becomes is called a conjugate pair
the original base becomes the conjugate acid; and the original acid becomes the conjugate base
NH3(aq) + H2O(l) NH4+
(aq) + OH–(aq)
Base Acid Conjugate Acid Conjugate Base
22
H–A + :B :A– + H–B+
acid base conjugate conjugate base acid
HCHO2 + H2O CHO2– + H3O+
acid base conjugate conjugate base acid
H2O + NH3 HO– + NH4+
acid base conjugate conjugate base acid
Brønsted-Lowry: Acid-Base ReactionsBrønsted-Lowry: Acid-Base Reactions
23
Conjugate PairsConjugate PairsIn the reaction H2O + NH3 HO– + NH4
+
H2O and HO– constitute an Acid/Conjugate Base pair
NH3 and NH4+ constitute a
Base/Conjugate Acid pair
24
Identify the Brønsted-Lowry Acids and Bases and Their Conjugates in the Reaction
Identify the Brønsted-Lowry Acids and Bases and Their Conjugates in the Reaction
H2SO4 + H2O HSO4– + H3O+
acid base conjugate conjugate
base acid
H2SO4 + H2O HSO4– + H3O+
When the H2SO4 becomes HSO4-, it lost an H+ so H2SO4 must be
the acid and HSO4- its conjugate base
When the H2O becomes H3O+, it accepted an H+ so H2O must be the base and H3O+ its conjugate acid
25
Identify the Brønsted-Lowry Acids and Bases and Their Conjugates in the Reaction
Identify the Brønsted-Lowry Acids and Bases and Their Conjugates in the Reaction
HCO3– + H2O H2CO3 + HO–
base acid conjugate conjugate acid base
HCO3– + H2O H2CO3 + HO–
When the HCO3 becomes H2CO3, it accepted an H+ so HCO3
- must be the base and H2CO3 its conjugate acid
When the H2O becomes OH-, it donated an H+ so H2O must be the acid and OH- its conjugate base
26
Practice – Write the formula for the conjugate acid of the following
Practice – Write the formula for the conjugate acid of the following
H2O
NH3
CO32−
H2PO4−
27
Practice – Write the formula for the conjugate acid of the following
Practice – Write the formula for the conjugate acid of the following
H2O H3O+
NH3 NH4+
CO32− HCO3
−
H2PO41− H3PO4
28
Practice – Write the formula for the conjugate base of the following
Practice – Write the formula for the conjugate base of the following
H2O
NH3
CO32−
H2PO4−
29
Practice – Write the formula for the conjugate base of the following
Practice – Write the formula for the conjugate base of the following
H2O HO−
NH3 NH2−
CO32− since CO3
2− does not have an H, it cannot be an acid
H2PO41− HPO4
2−
30
Arrow ConventionsArrow Conventions chemists commonly use two kinds of arrows
in reactions to indicate the degree of completion of the reactions
a single arrow indicates all the reactant molecules are converted to product
molecules at the end
a double arrow indicates the reaction stops when only some of the reactant molecules
have been converted into products
chemists commonly use two kinds of arrows in reactions to indicate the degree of
completion of the reactions
a single arrow indicates all the reactant molecules are converted to product
molecules at the end
a double arrow indicates the reaction stops when only some of the reactant molecules
have been converted into products
31
Strong or WeakStrong or Weak a strong acid is a strong electrolyte
practically all the acid molecules ionize, →
a strong base is a strong electrolyte practically all the base molecules form OH– ions, either through dissociation
or reaction with water, →
a weak acid is a weak electrolyte only a small percentage of the molecules ionize,
a weak base is a weak electrolyte only a small percentage of the base molecules form OH– ions, either
through dissociation or reaction with water,
a strong acid is a strong electrolyte practically all the acid molecules ionize, →
a strong base is a strong electrolyte practically all the base molecules form OH– ions, either through dissociation
or reaction with water, →
a weak acid is a weak electrolyte only a small percentage of the molecules ionize,
a weak base is a weak electrolyte only a small percentage of the base molecules form OH– ions, either
through dissociation or reaction with water,
32
Strong AcidsStrong Acids
The stronger the acid, the more willing it is to donate H
use water as the standard base
strong acids donate practically all their H’s
100% ionized in water
strong electrolyte
[H3O+] = [strong acid]
The stronger the acid, the more willing it is to donate H
use water as the standard base
strong acids donate practically all their H’s
100% ionized in water
strong electrolyte
[H3O+] = [strong acid]
HCl(aq) H+(aq) + Cl-(aq)
HCl(aq) + H2O(l) H3O+(aq)+ Cl-(aq)
33
Weak AcidsWeak Acids
weak acids donate a small fraction of their H’s
most of the weak acid molecules do not donate H to water
much less than 1% ionized in water
[H3O+] << [weak acid]
weak acids donate a small fraction of their H’s
most of the weak acid molecules do not donate H to water
much less than 1% ionized in water
[H3O+] << [weak acid]
HF(aq) H+(aq) + F-
(aq)
HF(aq) + H2O(l) H3O+(aq) + F-
(aq)
34
Polyprotic AcidsPolyprotic Acids
often acid molecules have more than one ionizable H – these are called polyprotic acids
the ionizable H’s may have different acid strengths or be equal
1 H = monoprotic, 2 H = diprotic, 3 H = triprotic
HCl = monoprotic, H2SO4 = diprotic, H3PO4 = triprotic
often acid molecules have more than one ionizable H – these are called polyprotic acids
the ionizable H’s may have different acid strengths or be equal
1 H = monoprotic, 2 H = diprotic, 3 H = triprotic
HCl = monoprotic, H2SO4 = diprotic, H3PO4 = triprotic
35
Polyprotic AcidsPolyprotic Acids
polyprotic acids ionize in steps
each ionizable H removed sequentially
removing of the first H automatically makes removal of the second H harder
H2SO4 is a stronger acid than HSO4
-
polyprotic acids ionize in steps
each ionizable H removed sequentially
removing of the first H automatically makes removal of the second H harder
H2SO4 is a stronger acid than HSO4
-
36
Incr
easi
ng A
cidi
tyIncreasing B
asicity
37
Strengths : Acids and Bases
commonly, Acid or Base strength is measured by determining the equilibrium constant of a substance’s reaction with water
HA + H2O A-1 + H3O+1
B: + H2O HB+1 + OH-1
the farther the equilibrium position lies to the products, the stronger the acid or base
the position of equilibrium depends on the strength of attraction between the base form and the H+
stronger attraction means stronger base or weaker acid