II. Properties of WaterO-Chem.pdfFig. 3.6: Five Critical Properties of Water 1. Ice and liquid water...
Transcript of II. Properties of WaterO-Chem.pdfFig. 3.6: Five Critical Properties of Water 1. Ice and liquid water...
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II. Propert ies of Water
1. Ice and Liquid water structure
2. Cohesion / Surface Tension
3. High Heat Capacity
4. Solvent Properties
5. Dissociation: Acids & Bases / pH
II. Organic Chemistry
A. Hydrocar bons--nonpolar
1. alkanes-only single bonds 2. alkenes- C=C double bonds 3. aromatic-cyclic based on benzene
B. Funct ional Groups: alcohol, aldehyde, ketone, carboxyl, amine, organophosphate, sulfhydral
1. polar bonds between C and more electronegative atoms (O and N) 2. Combine two functional groups ester = alcohol + acid 3. amide = amine + acid
C. Isomers
1. Same chemical formula but differ in arrangement of atoms in space 2. Enantiomers (Optical Isomers): C can be bonded to 4 different groups
in 2 ways producing molecules that are mirror images of one another that cannot be superimposed
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Water As A Solvent For Life
Water is essential for life on Earth
All living organisms require water more than any other substance
75% of the Earth’s surface is covered
with water
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104.5°
Fig. 3.2: Water: Structure and Properties
Water’s molecular structure and capacity to donate and accept hydrogen bonds give it unusual critical
properties that are significant for life
Hydrogen bond acceptors
Hydrogen bond donors
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Fig. 3.6: Five Critical Properties of Water 1. Ice and liquid water structure
Temperature ≤ 0°C Temperature > 0°C < 100°C • Ice is less dense than liquid water • Water is liquid at a relatively high temperature > 0°C
(Methane (CH4) is similar in size but liquid only below -161°C)
Hydrogen bond Liquid water
Hydrogen bonds break and re-form Ice
Hydrogen bonds are stable
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Hydrogen bonds hold water molecules
together in liquid
High Surface tension
Fig. 3.4
Fig. 3.3/3.4: Five Critical Properties of Water – 2. Cohesion
Water transport in plants
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Water has a high specific heat capacity specific heat capacity = amount of energy required to raise
temperature of 1 g of water by 1°C (1 calorie, 1 cal) Large bodies of water stabilize the air temperature.
Heat energy can be absorbed by breaking hydrogen bonds
Five Critical Properties of Water 3. Moderation of temperature
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Fig. 2.15 Fig. 3.7
A sphere of water molecules,
called a hydration shell, surrounds each solute ion
Fig. 2.15/3.7: Five Critical Properties of Water 4.Water as a solvent
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Fig. 3.8
Review solute concentration in aqueous solutions (Molarity) (page 51 – 52 of text)
Fig. 3.8: Five Critical Properties of Water 4. Water as a solvent (Cont’d)
(a) Lysozyme molecule in a nonaqueous environment
(b) Lysozyme molecule (purple) in an aqueous environment
(c) Ionic and polar regions on the protein’s surface attract water molecules.
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Five Critical Properties of Water 4. Water as a solvent (Cont’d)
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This reaction is frequently abbreviated as:
H2O H+ OH- +
The KW is the ion product of water,
Kw = [H+][OH-] = 1.0 x 10-14 M2 at 25°C
Thus, in pure water, [H+] = [OH-] = 1.0 x 10-7 M
Page 53
H3O+ (hydronium ion)
OH- (hydroxide ion)
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Fig. 3.9: pH SCALE - 1.0 x 10-7 M is a very small number and can change by orders of magnitude (powers of 10x) pH
“Physiological pH” (pH 6.5 – 8.0)
pH = -log[H+] = 7 in pure water at 25°C = neutral pH
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CH3-C O
O- CH3-C O
OH + H+
NH3 + H+ NH4+
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CH3COOH CH3COO- + H+
NH4+ NH3 + H+
HA A- + H+
Acid ionization constant, Ka = [H+][A-] [HA]
pKa = -log Ka
Ka pKa 1.8 x 10-5 M 4.7
5.8 x 10-10 M 9.2
pKa is a measure of propensity to dissociate: if pH < pKa the HA form predominates if pH > pKa the A- form predominates
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Buffers keep pH relatively constant in the range around pKa value by accepting or donating H+ from solution
Response to decrease [H+]
Response to increase [H+] CH3-C
O
O- CH3-C O
OH
[HA] >> [A-]
[A-] >> [HA]
[HA] = [A-]
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Organic Chemistry
The chemistry of molecules containing carbon bonded to other elements, principally: H, O, N, P, S …
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Hydrocarbons are Nonpolar (electrons are equally distributed) and do not mix freely with water
they are Hydrophobic.
109°
120°
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Fig. 4-3 Fig. 4.3: The Shapes of Three Simple Organic Molecules Name and Comment
Molecular Formula
(a) Methane
(b) Ethane
CH4
Ball-and- Stick Model
Space-Filling Model
(c) Ethene (ethylene)
C2H6
C2H4
Structural Formula
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Hydrocarbons -- organic compounds containing only carbon and hydrogen. These are the most reduced organic
compounds and react vigorously (i.e. burn) with oxygen.
CH4 + 2O2 CO2 + 2H2O + Heat
Heat
2 2 Methane
(natural gas) Oxygen Carbon Dioxide Water
+ + +
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Fig. 4.5: Various Hydrocarbons
Octane C8H18: A major component of gasoline.
(a) Length
Ethane 1-Butene
(c) Double bond position
2-Butene Propane
(b) Branching (d) Presence of rings
Butane 2-Methylpropane (isobutane)
Cyclohexane Benzene
H-C-C-C-C-C-C-C-C-H H H H H H H H H
H H H H H H H H
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Aromatic Hydrocarbons -- are a special class of hydrocarbons in which atoms are arranged in a ring structure and are connected by σ-bonds and a system of π-bonds around the ring. The simplest example is benzene, C6H6, and as shown below all atoms lie on a plane with bond angles of 120°
120°
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Fig. 4.4: Carbon also forms bonds with a variety of other Elements
O C O
Carbon dioxide (CO2) Urea
CO(NH2)
Hydrogen (valence = 1)
Oxygen (valence = 2)
Nitrogen (valence = 3)
Carbon (valence = 4)
H O N C
Urea
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Ethanol Acetone Acetic Acid
Functional Groups Here “R” represents the rest of the molecule
R–OH R–C H
O R–C
R’
O R–C
O
OH R–NH2 R–SH R–O–P–OH
O
OH Alcohol Aldehyde Ketone Carboxylic Acid Amine Sulfhydral Organic Phosphate
Carbonyls
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Fig. 5-2a Fig. 5.2a: The Synthesis of Polymers
(a) Dehydration reaction: synthesizing a polymer
Short polymer Unlinked monomer
Dehydration removes a water molecule, forming a new bond.
Longer polymer
1 2 3 4
1 2 3
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Organic molecules with certain functional groups can be joined by a covalent bond formed when a molecule of water is removed; this allows the creation of new types of organic molecules.
R-OH + HO-P-OH O
O- R-O-P-OH + H2O
O
O-
Linking Functional Groups Polymers
R–C O
OH + HO–R’ R–C
O
OH N-R’ H
+ H
Ester Amide
R–C O
O-R’ + H2O R–C
O
N-R’ H
+ H2O
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Fig. 4.6: Ester bonds link fatty acid carboxyl groups to OH- groups of Glycerol
Nucleus
Fat droplets
(b) A fat molecule a.k.a. Triglyceride
(a) Part of a human adipose cell
10 µm
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Isomers: Molecules that have the same chemical formula, i.e. the same number of each of the different kinds of atoms.
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Fig. 4.7: There are different classes of Isomers
cis isomer: The two X’s are on the same side.
trans isomer: The two X’s are on opposite sides.
L isomer D isomer
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Fig. 4-8 Fig. 4.8: Pharmacological Importance of Enantiomers
Drug
Ibuprofen
Albuterol
Condition Effective Enantiomer
Ineffective Enantiomer
Pain; inflammation
Asthma
S-Ibuprofen R-Ibuprofen
R-Albuterol S-Albuterol
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Thalidomide was first used as a sedative and anti-nausea medication, but was found to cause serious birth defects when pregnant women take it during their first trimester.