Basic Chemistry IV

Basic Chemistry IVVladimíra Kvasnicová

Water, solutions, and solubility• amphiprotic properties of water:

H2O + H2O H3O+ + OH-

• aqueous solutions (aq)HCl, NaOH, H2CO3, NH3

K = [H3O+] x [OH-] [H2O]2

• the equilibrium constant is CONSTANT:if concentration of H3O+ increasesthe concentration of OH- decreasesand vice versa

Dissociation of water:H2O ↔ H+ + OH- H2O + H+ + OH- ↔ H3O+ + OH-

H2O + H2O ↔ H3O+ + OH-

Kdis = [H3O+] x [OH-] [H2O]2

Kdis x [H2O]2 = [H3O+] x [OH-]Kdis x [H2O]2 = constant, because [H2O] is manifold higher than [H3O+] or [OH-]

Kw = constant = ionic product of waterKw = [H3O+] x [OH-]

Kw = [H3O+] x [OH-] = 10-14

pKW = pH + pOH = 14

pK = - log K pH = - log [H3O+] pOH = - log [OH-]

10-14 = [H3O+] x [OH-] / loglog 10-14 = log ([H3O+] x [OH-] ) log 10-14 = log [H3O+] + log [OH-] -14 = log [H3O+] + log [OH-] / x (-1) 14 = - log [H3O+] - log [OH-]

↓ ↓ ↓ pKW = pH + pOH 14 = 7 + 7 in pure water

Water, solutions, and solubility

H2O + H2O H3O+ + OH-

ionic product of water

Kw = [H3O+] x [OH-] = 10-14

pKw = pH + pOH = 14

pH = -log [H3O+]

http://www2.bc.cc.ca.us/bio16/images/02-14_ph_scale_1.jpg

pH= negative

logarithm of activity of

oxonium cations

acidic

neutral

basicpH scale is a logarithmic scale for expressing the acidity or alkalinity of a

solution

pH = - log a(H3O+)a = γ x ca = activityγ = activity coefficient c = concentration (mol /L) in diluted (mM) solutions: γ = 1 a = c

pH = - log c(H3O+)c(H3O+) = [H3O+] = molar concentration

simplification: c(H3O+) = cH+

pKW = pH + pOH = 14

=> water: [H3O+] = 10–7 (pH = 7) [OH-] = 10–7 (pOH = 7)

simplification: [H3O+] = [H+] = c(H+)=> pH = – log c(H+) pH = 0 – 14

pH 0 -------------- 7 --------------14 acidic neutral basic If [H+] decreases, [OH-] increases KW is 10-14

If [OH-] decreases, [H+] increases (= constant !)

strong acids (HA) [HA] = [H+]HA → H+ + A-

pH = - log c(H+) = - log cHA

strong bases (BOH) [BOH] = [OH-]BOH → B+ + OH-

pOH = - log cBOH

pH = 14 - pOH

weak acids (HA) [HA] ≠ [H+] Kdis ≤ 10–2

HA ↔ H+ + A-

Kdis = [H+] [A-] [H+] = [A-] [HA] = cHA Kdis = Ka

[HA] Ka = [H+]2

cHA

pH = ½ pKa - ½ log cHA

- log Ka = pKa

weak acids (HA) [HA] ≠ [H+] Kdis ≤ 10–

2

HA ↔ H+ + A-

Kdis = [H+] [A-] [H+] = [A-] [HA] = cHA Kdis = Ka

[HA] Ka = [H+]2

cHA Ka x cHA = [H+]2 / log log (Ka x cHA ) = 2 x log [H+] log Ka + log cHA = 2 x log [H+] / ½ ½ log Ka + ½ log cHA = log [H+] / x (-1) -½ log Ka - ½ log cHA = - log [H+] - log Ka = pKa

½ pKa - ½ log cHA = pH => pH = ½ pKa - ½ log cHA

weak acids (HA) [HA] ≠ [H+] Kdis ≤ 10–2

HA ↔ H+ + A-

pH = ½ pKa - ½ log cHA

weak bases (BOH) [BOH] ≠ [OH-] Kdis = [B+] [OH-]BOH ↔ B+ + OH- [BOH]

pOH = ½ pKb - ½ log cBOH

=> pH of basic solutions: pH + pOH = 14 pH = 14 - pOH

Important equations

pH = - log c(H+) pK = - log K pH + pOH = 14

ACIDS: pH = - log cHA

pH = ½ pKa - ½ log cHA

BASES: pOH = - log cBOH

pOH = ½ pKb - ½ log cBOH

pH = 14 – pOH

Exercisescalculate the pH of

• 0.1 M HCl• 0.001 M HCl• 0.05 M H2SO4

• 0.1 M NaOH• 0.001 M NaOH• 0.05 M Ba(OH)2

• pH = 1• pH = 3• pH = 1

• pOH = 1 → pH = 13• pOH = 3 → pH = 11• pOH = 1 → pH = 13

Dilution 100x pH is changed by 2 units!

Exercisescalculate the pH of

• 0.1 M acetic acid, pKa = 4.76

• 0.001 M acetic acid• 0.001 M H2CO3, pKa1 =

6,35 pKa2 =

10.25

• 0.1 M NH3, pKb = 4.74

• 0.001 M NH3

• pH = 2.88• pH = 3.88• pH = 4.68

• pOH = 2.87 → pH = 11.13

• pOH = 3.87 → pH = 10.13

Dilution 100x pH is changed by 1 unit!

Organic compounds

• „compounds of carbon“• hydrocarbon skeleton: C, H

saturated: CH3-(CH2)n-CH3

unsaturated: -CH=CH- or –C=C-• heteroatoms: O, N, S, halogens

heterocyclic compounds hydrocarbon derivatives (in functional groups)

• aliphatic or aromatic compounds

Shape of moleculesσ-bond C-C

π-bond C=CC≡C

Alkanes– hybridization sp3 – tetrahedral

shape (4 bonds)

ethane

Alkenes– hybridization sp2 – trigon (3 and 1 )

Alkynes– hybridization sp – linear (2 and 2 )

ethene

ethyne

Aromatic compounds

• delocalization of π-elektrons

• more resonance structures

• planar molecules

• Hűckel rule: 4n + 2 = number of -electronsn = 1, 2, 3,...

inorganic compounds organic compoundshigh melting points low melting pointsmost inorganic compounds are soluble in water

most organic compounds are insoluble in water

not soluble in organic liquids are soluble in organic liquidsmost inorganic compounds conduct an electric current

don´t conduct electricity

met- et- prop- but- pent- hex-

hept- oct- non- dec-

1 2 3 4 5 6 7 8 9 10

Chemical properties

• hydrocarbons are hydrophobic (= lipophilic) because are nonpolar

• hydrocarbon derivatives:polar functional group + nonpolar tail

• reactivity: multiple bonds functional groups

• complete oxidation (= burning) of a hydrocarbon skeleton → CO2 + H2O

Important chemical reactions of organic compounds

1. substitution (= replacement)CH4 + Cl2 → CH3Cl + HCl

2. addition (multiplicity of chemical bond is lowered)CH2=CH2 + H2O → CH3-CH2-OH

3. elimination (new multiple bond is often formed,small molecule is released)

CH3-CH2-OH → CH2=CH2 + H2O 4. rearrangement (= formation of an isomer)

CH2=C(OH)-COOH → CH3-C(O)-COOH

Isomerismisomers = compounds having the same molecular formula

but different molecular structures (costitution) ordifferent arrangements of atoms in space (configuration)

a) constitutional (structural) isomers different type of a hydrocarbon chain different position of a substituent or a multiple bond different functional groups keto-enol isomers (= tautomers)

b) configurational isomers (stereoisomers) optical isomers (= enantiomers) are „mirror images“ cis-trans isomers (= geometrical isomers)

Hydrocarbon derivatives

carboxylic acid R-COOH• aliphatic / -oic acid (-dioic acid)

/ - tricarboxylic acid• cyclic / - carboxylic acid

1. hydrocarbon –oic acid (propanoic acid)2. common names (propionic acid)

reactions:dissociation → carboxylate (= anion) reduction → aldehyde

Hydrocarbon derivatives

sulfonic acid R-SO3H

• sulfo- / sulfonic acid

1. hydrocarbon sulfonic acid (methane sulfonic acid)

reactions: dissociation → sulfonate (= anion) reduction → thiol

Hydrocarbon derivatives

aldehyde R-CHO• aliphatic formyl- / -al• cyclic - carbaldehyde

1. hydrocarbon –al (methanal)2. common names (formaldehyde)

reactions:oxidation → carboxylic acidreduction → primary alcohol

Hydrocarbon derivatives

ketone R1-CO-R2

• aliphatic oxo- or keto- / -one• cyclic unsaturated diketones = quinones

1. hydrocarbon –one (propanone)2. hydrocarbon rests ketone (dimethyl ketone)3. common names (acetone)

reactions:reduction → secondary alcohol

Hydrocarbon derivatives

alcohol R-OH• aliphatic hydroxy- / -ol (-diol, -triol)• aromatic = phenols common names• sulfur-containing = thiols sulfanyl- / -thiol

1. hydrocarbon –ol (methanol)2. hydrocarbon rest alcohol (methyl alcohol)

reactions:oxidation → aldehyde or ketonedehydration → unsaturated hydrocarbon

Hydrocarbon derivatives

amine R-NH2 R1-NH-R2 R1-N(R2)-R3

• amino- / -amine (-diamine)

1. hydrocarbon rest(s) –amine (propylamine)2. hydrocarbon -amine (propaneamine)

reactions:oxidation → nitro compoundprotonation → ammonium cation

Hydrocarbon derivatives

ether R1-O-R2

• alk(yl)oxy- / -ether• sulfur-containing = sulfide / - sulfide

R1-S-R2

1. hydrocarbon rests ether (ethyl propyl ether)

Hydrocarbon derivatives

halogen derivative R-X X = F, Cl, Br, Ihalogeno- /

(fluoro-, chloro-, bromo-, iodo-)

1. halogeno- hydrocarbon (chloromethane)

nitro derivative R-NO2

nitro- /1. nitro- hydrocarbon (nitromethane)