Acids and Bases 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.

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


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


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+


H2O + NH3 HO– + NH4+


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


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



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


H2O

NH3

CO32−

H2PO4−

27



H2O H3O+

NH3 NH4+

CO32− HCO3

−

H2PO41− H3PO4

28

Practice – Write the formula for the conjugate base of the following


H2O

NH3

CO32−

H2PO4−

29



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

Acids and Bases 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.

Documents

binary acids

hfstructure of acids

germinationdigestive

acids andbasesrna

structure of acidsoxy

neighboring amino acids

amine groupsamino acids

acidicthe h