Module 7 Flashcards
1
Q
Bond angle of 4 VSEPR groups?
A
109.5 - tetrahedral
2
Q
Bond angle of 3 VSEPR groups?
A
120 - trigonal planar
3
Q
Bond angle of 2 VSEPR groups?
A
180 - linear
4
Q
Formula of Alkanes
A
CnH2n+2
5
Q
Formula of Alkenes
A
CnH2n
6
Q
Formula of Alkynes
A
CnH2n-2
7
Q
Which intermolecular force occurs between hydrocarbon molecules (and affects the strength of the IMF)
A
Dispersion forces
8
Q
What is packing?
A
How the molecules fit together
The closer molecules pack, the higher the IMF are
9
Q
What makes molecules pack better
A
Smaller molecules of unbranched molecules
10
Q
Order of boiling points for alkenes, alkanes, and alkynes
A
Alkenes<Alkanes<Alkynes
11
Q
Why do alkynes have the highest boiling point?
A
Linear geometry around the triple bond allows for closer packing
12
Q
Forces acting within dissolution
A
- Solute - solute cohesive forces
- Solvent - solvent cohesive forces
- Solute - solvent adhesive forces
13
Q
Forces when a substance is soluble
A
Adhesive forces are strong enough to break cohesive forces (causing mixing at molecular level)
14
Q
Forces when substance is insoluble
A
Cohesive forces are too strong to be broken by adhesive forces
15
Q
Forces within hydrocarbons
A
Dispersion
16
Q
Forces within water (solvent)
A
Dispersion, H-bonding, dipole-dipole
17
Q
Adhesive forces between hydrocarbons and water
A
Dispersion forces (but not strong enough to strong cohesive bonding)
18
Q
Why does density increase with increasing molar mass
A
Increase in molar mass –> increase in dispersion forces –> allows molecules to attract closer –> density increases
19
Q
What would happen if you mix water and an alkane?
A
Would not mix
Alkane would be at the top as it is at a lower density
(forms two phases)
20
Q
What is volatility?
A
Ability of a liquid to form a vapour
21
Q
Relationship between volatility and boiling point
A
The lower boiling point the higher the volatility
22
Q
Why do hydrocarbons have a relatively low volatility?
A
IMF are weak
Hydrocarbons are non-polar so the only IMF are weak dispersion forces
23
Q
What is viscosity?
A
Resistance to fluid flow
24
Q
Why do hydrocarbons generally have a low viscosity?
A
Weak IMF - dispersion forces between the molecules
25
What is a homologous series?
Compounds with the same functional group, but differ in the number of repeating units (CH2)
26
Halo-
(Halides)
F, Cl, Br, I
27
Hydroxyl (Alcohols)
- OH
'-ol'
28
Amino (Amine)
-N- -
'-amine'
29
Amide (Amide)
- - N-C=O
'-amide'
30
Carbonyl (Aldehyde)
H-C=O
'-al'
(at the end)
31
Carbonyl (Ketone)
-C=O
'-one'
(always in middle)
32
Carboxyl (Carboxylic Acid)
HO-C=O
'-oic acid'
33
Primary Alcohols
Have one other C bonded to C bearing the -OH
34
Secondary Alcohols
Have two other C bonded to C bearing the -OH
35
Tertiary Alcohols
Have three other C bonded to C bearing the -OH
36
Primary Amine
Directly bonded to one alkyl group
37
Secondary Amino
Directly bonded to two alkyl group
38
Alkyl group connected to N (prefix)
N
39
What are structural isomers?
Same molecular formula, but arranged differently
Different structural formula
CANNOT BE IDENTICAL EITHER
40
Three types of structural isomers:
- Chain
- Position
- Functional group
41
Chain isomers
Rearrangement of carbons in the backbone
E.g. different number of carbons in the longest chain, or different branching
E.g. hexane and 2-methylpentane
42
Position Isomers
Molecules have the same carbon skeleton and functional group, but the functional group is in a different location
E.g. alkenes but-1-ene, and but-2-ene
43
Functional Group Isomers
Result when atoms in the molecules are arranged to form different functional groups
Functional group isomers belong to different homologous series
e.g. propanoic acid and 1-hydroxypropan-2-one (look it up to visualise)
44
Combustion Reactions
Fuel + O2(g) --> CO2(g) + water (l)
45
Incomplete Combustion products
Soot - C (s)
Carbon Monoxide - CO (g)
46
What is bond energy?
The average energy required to break 1 mol of a bond in the gas phase
47
Addition Reactions of Alkenes (4)
1. Hydrogenation
2. Halogenation
3. Hydrohalogenation
4. Hydration
48
Hydrogenation
Alkene to alkane
Reagent: H2
Catalyst: Metal catalyst
49
Halogenation
Alkene to alkane (with 2 halogens)
Only with Br2, Cl2 (Bromination and chlorination)
Reagent/s: Br2/Cl2
F2 and I2 are too reactive or too slow
50
Hydrohalogenation
Alkene to alkane (with 1 halogen)
Reagent/s: hydrogen halides
Forms two products (major and minor)
51
Markovnikov's Rule
The hydrogen atom will go to the carbon with the most hydrogens (to form the major product)
52
Hydration
Alkene to alcohol
Reagent: H2O
Conditions: dil. H2SO4
Markovnikov's Rule applies
53
Substitution reactions of Alkanes
Carried out with bromine and chlorine
Requires UV light
Produces a haloalkane AND a hydrogen halid
There can be haloalkane isomers as well
54
Substitution reactions of alkanes with excess Cl2/Br2
The reaction can occur until all of the hydrogen atoms have been replaced
e.g. could produce CH3Cl or CCl4
55
Bromine test for unsaturation (Procedure)
1. Place 3.0ml of the unknown organic liquids (cyclohexane and cyclohexene) in each test tube labelled A and B
2. Add o.5mL of bromine to each test tube
3. Record observations
56
Bromine test for unsaturation (safety - bromine)
Hazard:
Skin/eye irritant, lung sensitiser
Risk: Can cause severe eye damage and skin rashes. If inhaled, can lead to breathing difficulties
Safety Precaution:
PPE (gloves, labcoat, goggles)
Under fumehood, highly ventilated area
57
Bromine test for unsaturation (safety - cyclohexane/ene)
Hazard:
Skin/eye irritant, flammable, toxic by inhalation or ingestion
Risk: Can lead to headaches, dizziness, nausea, and vomiting
Safety Precaution:
PPE (gloves, labcoat, goggles)
Under fumehood, highly ventilated area
Avoid ignition sources, e.g. powerpoints
58
Bromine test for unsaturation (observations)
Deep red solution: cyclohexane --> none of the Br2 has reacted
Colourless: cyclohexene: the Br2 has reacted and red colour has faded
59
Bromine test for unsaturation (why cyclos?)
They are liquids at room temperature, whereas hexane/ene are gaseous at rt
60
Bromine test for unsaturation (special conditions)
No exposure to UV light as the cyclohexane would react with the Br2!
61
Bromine test for unsaturation (phases)
Hexane: hexane on tip with reddish water on bottom
Hexene: Organic phase on top, colourless water phase
62
Non-polar and polar regions of alcohols
Non-polar: carbon chain
Polar: O: - H
63
Intermolecular forces that polar region forms
H-bonding, dipole-dipole, dispersion forces (in the chain) (that are stronger that water)
64
Chain length and dispersion forces (alcohols)
Dispersion force strength increases as the chain length increases
65
Boiling Point trend (alcohols)
Increases as chain length increases because the additional 'CH2' bond added increases the mass --> increases dispersion forces --> more thermal energy is needed
66
Methanol and ethanol's 'high' melting points
Packing
They can pack more densely, therefore, the effective IMF force between the molecules are greater
--> more thermal energy needed to break the IMF
67
Pos. of Hydroxyl groups (alcohols) and boiling point
Primary: highest
Secondary
Tertiary: lowest
Why?
Secondary and tertiary have alkyl groups adjacent to the OH, therefore stop the OH group from getting close together and restricts the FORMATION OF STRONG H-BONDS
68
Solubility of Primary Alcohols (in water)
Meth to Prop is miscible in water
Why?
The short HC chains do not disrupt solvation
The OH group forms H-bonds with water
However, longer HC chains have many strong cohesive bonds and cannot be broken by weak adhesive dispersion forces
69
Solubility of Primary Alcohols (in non-polar substances)
More soluble in non-polar organic substances, e.g. hexane, benzene as the length of the HC chain increases
Why?
The alkyl chain can form strong dispersion forces with other non-polar substances.
These are strong enough to disrupt the cohesive hydrogen bonds in the alcohol --> they can be solvated
70
Why are small alcohols good solvents for dissolving polar and non-polar substances?
Polar hydroxyl group can form polar interactions e.g. ion-dipole forces, H-bonding, and dipole-dipole forces with polar and ionic substances
Non-polar HC chain can form dispersion forces with non-polar substances
Example: ethanol: commonly used in pharmacy as medicines can be non-polar
71
Dehydration of Alcohols (Elimination)
Alcohol to alkene
Reagent: Concentration H2SO4
or even Al2O3 as a catalyst
Conditions: Heat
Products: Alkene and water
72
Zaitsev's Rule
If multiple alkenes can be formed then the major product will the the double bond connected to the carbons connected to the most carbons
73
Type of alcohol (dehydration)
Tertiary are the most reactive, then secondary, then primary
74
Substitution Reactions (w/ alcohols)
Alcohol to haloalkane (+ water)
Reagent: Hydrogen halide
Same trend for dehydration (tertiary react rapidly at room temp while the others may need higher temps)
75
Strongest hydrogen halide to use for substitution of alcohol
HI, then HBr, then HCl
76
Lucas Reagent
To increase the reactivity of HCl: use Lucas Reagent: ZnCl2
77
Oxidation (of alcohols)
Reagents: Cr2O7^-2 or MnO4-
Conditions: H+
78
Oxidation of Primary Alcohols
Oxidises to a carboxylic acid
79
PCC?
Milder oxidising agent to get to the middle step and get an aldehyde from an alcohol
80
Oxidation of Secondary Alcohol
Oxidised to a ketone
81
Oxidation of Tertiary Alcohols
Cannot be oxidised as the alcohol carbon has no H atoms
82
Dichromate colours
Orange to Green
83
Permanganate colours
Purple to colourless
84
Reactivity times
Quick colour change? Primary
Slow colour change? Secondary
No colour change? Tertiary
85
Production of alcohols in the industry
Hydration of alkenes or substitution of haloalkanes
86
Production of alcohols (to consume or to be used as fuel (e.g. ethanol)
Fermentation (glucose)
87
Reason for primary alcohols reacting the fastest and tertiary alcohols the slowest
Alkyl groups hinder the approach of the OH- to the carbon
There is more room for the OH- group in a primary alcohol
88
Most reactive halogen as a leaving group
Iodine: weakest bond energy between a C-I, so this halogen would react the fastest
89
Fermentation Equation
(Glucose to Ethanol)
C6H12O6(aq) --> 2C2H5OH(aq) + 2CO2(g)
90
Conditions for fermentation
1. Zymase (found in yeast)
2. Temp. (30-40degC) (may depend on yeast strain)
3. Anaerobic environment
4. Aqueous solution of sugar
91
Why anaerobic?
In the presence of oxygen the yeast will respire will causes the oxidation of ethanol to acetic acid, CO2 or H2)
92
Why aqueous?
1. Yeast produce ethanol concentrations up to about 15%v/v otherwise the yeast suffer at a concentration higher
2. An aqueous solution allows for a larger amount of ethanol to be produced without exceeding the 15% concentration
93
Source of hydrocarbons from Earth
Petroleum
94
Problems with petroleum?
Finite and non-renewable
95
Factors to be considered when selecting alternatives to petroleum
1. Fuel efficiency
2. Renewable
3. Widely available
4. Cost effective
5. Environmentally friendly
96
What are biofuels derived from?
Biomass
97
What is biomass?
Biological material from living or recently living organisms
98
Examples of biomass?
Corn grain
Dead animals
Food waste
99
Types of biofuel
1. Bioethanol
2. Biogas
3. Biodiesel
100
Production of bioethanol
Produced from the fermentation of monosaccharides e.g. glucose and fructose
101
What is biogas?
A mixture of gases, such as methane, carbon monoxide, and hydrogen released by natural breakdown of organic matter by anaerobic bacteria
102
Production of biogas (to be used)
Waste is placed in a digester which contains anaerobic bacteria. The gas released in the decay process is collected by gas outlets.
103
How is biogas used?
Combusted as fuel to generate electricity or heat boilers for industrial processes and in households for cooking and heating water
104
What is biodiesel?
Liquid mixture of long hydrocarbon chain esters
105
Production of biodiesel?
Produced from animal fats or vegetable oils
Oils from commercial cooking such as coconut, soybean, sunflower, canola and palm oil is used
Production is called transesterification
106
Advantages of Biofuels (as alternative fuels)
1. Renewable
2. Reduced CO2 production (but not carbon neutral)
3. Less toxic and environment
4. harming gases are produced
5. Less toxic if spilled
6. Reduced SO2, CO, and C
107
Advantages of lower carbon dioxide emissions?
Reduces greenhouse effect
108
Disadvantages of Biogas (as alternative fuels)
1. Need for large scale crop produce (get a sufficient amount of starch to make a replacement sufficient enough to replace petroleum fuels)
2. Some negative environmental impacts: large amounts of fertile land is needed
3. Larger amount of ethanol is needed to deliver the same energy
4. Engines may require technological modifications
109
Polarity of O-H bond in a carboxylic acid
Highly polar
110
KA and Carboxylic Acids
The higher the KA, the stronger the acid (the smaller pKA)
111
Chain length and carboxylic acid strength
Acid strength decreases with increasing chain length
112
Chain length and carboxylic acid strength (explanation)
Alkyl groups are capable of donating electron density: C is more e-neg, so it pulls e- density away from the H
113
Halogens and carboxylic acids strength)
Acid strength increases with electronegative substituents (halogens)
114
Which halogen would produce the strongest acid?
F (3 optimal)
115
Amines (basicity)
Weak bases
116
Chain length and amine strength
Base strength increases with increasing chain length
117
Chain length and carboxylic acid strength (explanation)
1. Alkyl groups donate electron density to the electronegative nitrogen atom (making it more negatively charged)
2. The longer the chain the greater the negative charge on the N
3. Therefore, it accepts H+ more readily and stabilities the +ive charge - making it a stronger base
118
Substitution (of halogens) and carboxylic acid strength
Base strength decreases with e-neg substituents on the C chain because they pull electrons away from the N
119
Amides (basicity)
Neutral!
120
Why are amides neutral?
The oxygen atom pulls electron density away from the N, making difficult to accept H+
121
Reactions of Carboxylic Acids
MASH2, BASH2O, CASH2OCO2
122
Reactions of amines
Amine + acid --> ammonia salt
123
Polarity of amines, amides, and carboxylic acids
Polar
124
IMF in amines, amides, and carboxylic acids
Dispersion, H-bonding, dipole-dipole
125
Why do amides have the highest boiling point (out of amines, amides, and carboxylic acids)
Number of H-bongs each functional group can form
126
Solubility of SMALL amines, amides, and carboxylic acids in water
Soluble: they dissolve completely in water
127
Longer HC chains of amines, amides, and carboxylic acids and solubility
Solubility decreases as the chain becomes longer
128
Solubility of SMALL amines, amides, and carboxylic acids in non-polar organic solvents
Immiscible
129
Solubility of SMALL amines, amides, and carboxylic acids in non-polar organic solvents (explanation)
Adhesive bonds (IMF of H-bonding) between water and the compound replace the similar cohesive IMF forces of water and the similar cohesive IMF forces of the organic compound
130
Longer HC chains of amines, amides, and carboxylic acids and solubility (explanation)
Relatively strong cohesive dispersion forces between the non-polar HC chain cannot be replaced by the weak dispersion forces between water and the weak adhesive dispersion forces between water and the organic compound
131
What are esters made from
Alcohol + carboxylic acid
132
What type of reaction is esterification?
Condensation
EXISTS IN EQUILIBRIUM
133
Catalyst for esterification + why
H2SO4
Catalyst results in a different reaction path for the reaction to follow --> ideally with a lower activation energy
134
Why is H2SO4 also used as a dehydrating agent?
When you remove water, the reaction shifts in the forward direction (acc. LCP), thus more product is formed
135
Conditions for esterification:
Catalyst: H2SO4
Reflux: Reaction mixture is heated with a condenser so that volatile reactants and products are returned to the reaction without any loss
136
Apparatus for esterification:
1. Condensing tube (condenser)
Prevents volatile substances from escaping by cooling to condense escaping vapours
2. Boiling chips (in reaction mixture)
Provides a surface for bubbles to form, promoting even boiling
3. Water bath
Non-ignition heat source
4. Open top (with cotton)
Prevents pressure build up
137
Safety precautions for production of esters
Avoid ignition sources
138
Procedure for Esterification
1. Place 10mL of carboxylic acid and 10mL alcohol in a round bottomed flask with boiling chips
2. Add 3mL concentrated sulfuric acid to the mixture
3. Attach a reflux condenser and heat mixture under reflux for 1 hour
4. Allow mixture to cool and transfer contents to a separating funnel with a large volume of distilled water
5. Shake the mixture and then allow it to separate into two layers. Discard the aqueous layer
6. Add a small amount of saturated sodium carbonate solution to the organic layer until bubbling (CO2) ceases. Add water and shake the mixture. Allow the mixture to separate into two layers. Discard the aqueous layer.
7. Add a drying agent to the organic layer (e.g. MgSO4, any salt as it attracts water). Filter off drying agent
8. Distill for further purification
*separate using a separating funnel
139
What are soaps
The salts of fatty acids
140
Structure of soaps
Consist of a carboxylate anion with a long hydrocarbon chain, and a positively charged sodium or potassium cation (don't play a part in the cleaning action of soaps)
Hydrophilic carboxylate head group
Hydrophobic chain
141
Soaps are surfactants
Surface active agent
142
How do surfactants work?
Reduce the surface tension of water to allow grease and dirt to be solubilised
143
How do soaps work?
Polar anionic head is hydrophilic and allows soap to interact with the water
Non-polar hydrocarbon tail is hydrophobic and allows soap to bind to grease and dirt
144
Steps of the cleaning action of soaps (3)
1. Dissolution
2. Adsorption
3. Emulsification
145
Dissolution (of soaps in water)
Hydrophilic head of a soap ion interacts with water molecules via ion-dipole forces and H-bonding
The non-polar HC chain is hydrophobic and strongly repelled by water molecules
They self-assemble into the most stable arrangement, a micelle (draw picture)
146
Adsorption
Grease and oil consist of non-polar molecule
Hydrophobic tails of the soap molecules dissolve in the grease via dispersion forces and orient themselves as such (draw picture)
147
Emulsification
With agitation, the grease layer breaks up into smaller spherical emulsion droplets with the hydrophilic surfactant head groups interacting with the water via ion-dipole forces, and the hydrophobic surfactant tails adsorbed into the grease.
Emulsion droplets are dispersed in the water and can be washed away (draw picture)
148
Issues with soap
Soap ions must be dissolved in order to have a cleaning effect.
Soaps can also form insoluble salts (scum) in hard water, which contains a high concentration of divalent metal ions such as Ca 2+ and Mg2+
149
Why are soaps ineffective and acidic or hard water
The carboxylate is removed as a free fatty acid at a low pH. In hard water insoluble Mg or Ca salts of the carbohydrates are formed and thus the soap is removed.
150
Types of synthetic detergents
Anionic
Cationic
Non-ionic
151
Anionic Detergents
Have a negatively-charged, polar head
Contains a sulfonate or sulfate group instead of a carboxylate head group
152
Anionic Detergents - effectiveness in hard or acidic water
They do not form scum (metal precipitates with metal ions
Still reduced in hard and acidic water as the metal ions and hydrogen ions will still react with them, decreasing the polarity of the head group
153
Uses of anionic detergents
Cleansers found in shampoos, dishwashing detergents and washing powders
154
Cationic Detergents
Positively charged, polar head
Known as fatty amine salts
155
Cationic Detergents - effectiveness in hard or acidic water
Do not form precipitates since they have a positive charged they are repelled from positively charged cations such as Ca2+ and Mg2+
156
Uses of Cationic Detergents
Fabric softeners - they form a waxy coating to reduce static and tangling and give a softer feel
Hair conditioners
Very low biodegradability
157
Non-ionic Detergents
Polar groups such as ethoxylates or sugars
Uncharged
158
Non-ionic Detergents - effectiveness in hard or acidic water
Do not form precipitates in water
Dishwashing powders, cosmetics
159
Environmental impact of surfactants
Detergents are generally less biodegradable
They can damaging mucus membranes in wildlife and cause excessive frothing of waterways which decreases sunlight penetration
(not done pg 277)
160
What is a polymer
A long chain molecule made up of repeating units (monomers) joined by covalent bonds
161
Addition polymers
Made by adding unsaturated monomers to each other without eliminating any atoms
162
Condensation Polymers
Difunctional monomers with the elimination of small molecule such as water or methanol
163
Properties of Polymers (3)
1. Melting point (softening)
2. Mechanical strength
3. Flexibility
164
Chain Branching
Polymers can form branched or unbranched chains
165
Unbranched
Closely packed in an orderly fashion to form a rigid crystalline solid
Unbranched polymer chains align so they lie parallel
166
Effect of close packing on the strength of IMF between chains (polymers)
The chains are able to come closer together. Therefore, the effective IMF is increasing
167
Branched polymer
They are unable to align closely to form an amorphous solid (crystalline solid) with weak IMF forces between the chains
168
Effect of side groups (bulkier)
Bulkier side groups: makes material more rigid and brittle
Bulkier side groups also increase the strength of IMF forces between polymer chains - giving a harder polymer
169
How do bulkier side groups lead to a more rigid polymer
Straighten up the strand of the polymer
170
Chain length (increasing) and the MP, rigidity and hardness of polymers
The molecular weight increases when the chain length increases therefore dispersion forces between these strands increases
171
Ethene (x2 polymers)
Structure (think or draw)
Name
Properties
Used for
1. Name - LD Polyethylene
Properties: flexible, low m.p., soft
Used for: Flexible food bags, disposable packaging
2. Name: HD Polyethylene
Properties: rigid, hard
Used for: Crinkly garbage bags, milk bottles
172
Chloroethene
Structure (think or draw)
Name
Properties
Used for
Name: Polyvinylchloride
Properties: Hard and rigid, flexible with plasticisers, flame and chemical resistant
Used for: Pipes, flooring, vinyl records
173
Ethenylbenzene
Structure (think or draw)
Name
Properties
Used for
Name: Polystyrene
Properties: Stiff, brittle, transparent, hard, high softening temperature
Used for: CD cases, heat insulation foams, floatation devices
174
Tetrafluoroethene
Structure (think or draw)
Name
Properties
Used for
Name: Polytetrafluoroethene
Properties: Hard, rigid, flame-resistant, low friction
Used for: non-stick coating for cooking pans
