Transcript Basic Chemistry IV - Univerzita Karlova v Praze

Basic Chemistry IV
Vladimíra 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+ increases
the concentration of OH- decreases
and vice versa
Dissociation of water:
H2O ↔ H+ + OHH2O + H+ + OH- ↔ H3O+ + OH-
H2O + H2O ↔ H3O+ + OHKdis = [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 water
Kw = [H3O+] x [OH-]
Kw = [H3O+] x [OH-] = 10-14
pKW = pH + pOH = 14
pOH = - log [OH-]
pK = - log K
pH = - log [H3O+]
10-14
log 10-14
log 10-14
-14
14
↓
pKW
14
[H3O+] x [OH-]
/ log
log ([H3O+] x [OH-] )
log [H3O+] + log [OH-]
log [H3O+] + log [OH-]
/ x (-1)
- log [H3O+] - log [OH-]
↓
↓
=
pH
+
pOH
=
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+]
acidic
neutral
pH
= negative logarithm
of activity of
oxonium cations
basic
pH scale is a logarithmic scale
for expressing the acidity or
alkalinity of a solution
http://www2.bc.cc.ca.us/bio16/images/02-14_ph_scale_1.jpg
pH = - log a(H3O+)
a=γxc
a = activity
γ = 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
If [OH-] decreases, [H+] increases
KW is 10-14
(= constant !)
strong acids (HA)
HA → H+ + A-
[HA] = [H+]
pH = - log c(H+) = - log cHA
strong bases (BOH) [BOH] = [OH-]
BOH → B+ + OHpOH = - log cBOH
pH = 14 - pOH
weak acids (HA)
HA ↔ H+ + AKdis = [H+] [A-]
[HA]
[HA] ≠ [H+]
[H+] = [A-]
Ka
[HA] = cHA
Kdis ≤ 10–2
Kdis = Ka
= [H+]2
cHA
pH = ½ pKa - ½ log cHA
- log Ka = pKa
weak acids (HA)
HA ↔ H+ + AKdis = [H+] [A-]
[HA]
[HA] ≠ [H+]
[H+] = [A-]
[HA] = cHA
Ka
Kdis ≤ 10–2
Kdis = 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+ + A-
[HA] ≠ [H+]
Kdis ≤ 10–2
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
Exercises
calculate the pH of
• 0.1 M HCl
• 0.001 M HCl
• 0.05 M H2SO4
• pH = 1
• pH = 3
• pH = 1
• 0.1 M NaOH
• 0.001 M NaOH
• 0.05 M Ba(OH)2
• pOH = 1 → pH = 13
• pOH = 3 → pH = 11
• pOH = 1 → pH = 13
Dilution 100x  pH is changed by 2 units!
Exercises
calculate the pH of
• 0.1 M acetic acid, pKa = 4.76 • pH = 2.88
• pH = 3.88
• 0.001 M acetic acid
• 0.001 M H2CO3, pKa1 = 6,35 • pH = 4.68
pKa2 = 10.25
• 0.1 M NH3, pKb = 4.74
• 0.001 M NH3
• pOH = 2.87
• pOH = 3.87
→ pH = 11.13
→ 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 molecules
σ-bond
C-C
π-bond
C=C
C≡C
Alkanes
– hybridization sp3 – tetrahedral
shape
(4  bonds)
ethane
Alkenes
– hybridization sp2 – trigon (3  and 1 )
Alkynes
ethene
– hybridization sp – linear (2  and 2 )
ethyne
Aromatic compounds
• delocalization of π-elektrons
• more resonance structures
• planar molecules
• Hűckel rule:
n = 1, 2, 3,...
4n + 2 = number of -electrons
met-
et-
1
2
prop- but- pent- hex- hept- oct- non- dec3
4
5
inorganic compounds
6
7
8
9
organic compounds
high melting points
low melting points
most inorganic compounds are
soluble in water
most organic compounds are
insoluble in water
not soluble in organic liquids
are soluble in organic liquids
most inorganic compounds conduct
an electric current
don´t conduct electricity
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
Isomerism
isomers = compounds having the same molecular formula but
different molecular structures (costitution) or
different 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
1.
hydrocarbon –oic acid
(propanoic acid)
2.
common names
(propionic acid)
reactions:
/ - carboxylic acid
dissociation → carboxylate (= anion)
reduction → aldehyde
Hydrocarbon derivatives
sulfonic acid
R-SO3H
•
sulfo- / sulfonic acid
1.
hydrocarbon sulfonic acid
reactions:
(methane sulfonic acid)
dissociation → sulfonate (= anion)
reduction → thiol
Hydrocarbon derivatives
aldehyde
R-CHO
•
aliphatic
•
cyclic
1.
hydrocarbon –al
(methanal)
2.
common names
(formaldehyde)
reactions:
formyl- / -al
- carbaldehyde
oxidation → carboxylic acid
reduction → primary alcohol
Hydrocarbon derivatives
ketone
R1-CO-R2
•
aliphatic
•
cyclic unsaturated diketones = quinones
1.
hydrocarbon –one
(propanone)
2.
hydrocarbon rests ketone
(dimethyl ketone)
3.
common names
(acetone)
reactions:
oxo- or keto- / -one
reduction → secondary alcohol
Hydrocarbon derivatives
alcohol
R-OH
•
aliphatic
hydroxy- / -ol
•
aromatic = phenols
common names
•
sulfur-containing = thiols
sulfanyl- / -thiol
1.
hydrocarbon –ol
(methanol)
2.
hydrocarbon rest alcohol
(methyl alcohol)
reactions:
(-diol, -triol)
oxidation → aldehyde or ketone
dehydration → 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 compound
protonation → ammonium cation
Hydrocarbon derivatives
ether
R1-O-R2
•
alk(yl)oxy- / -ether
•
sulfur-containing = sulfide
R1-S-R2
1.
hydrocarbon rests ether
/ - sulfide
(ethyl propyl ether)
Hydrocarbon derivatives
halogen derivative
R-X
X = F, Cl, Br, I
halogeno- /
(fluoro-, chloro-, bromo-, iodo-)
1.
halogeno- hydrocarbon
nitro derivative
(chloromethane)
R-NO2
nitro- /
1.
nitro- hydrocarbon
(nitromethane)