Chapter 13 - Organic Chemistry & Modern Lifestyles

Question 0

How are polymers formed?

Answer 0

• By the reaction between small molecules known as monomers.
• These monomers combine in a process known as polymerization.

Question 1

What is addition polymerization?

Answer 1

• When Alkenes can join together to form polymers.
• In this reaction, each monomer molecule undergoes an addition reaction in which the double bond in the molecule is broken and new single carbon-carbon bonds form, in a stepwise fashion, as the backbone of carbon atoms grows larger.

Question 2

What do complex mechanisms of polymerization usually involve?

Answer 2

The use of a catalyst and a substance known as an initiator (or free radical initiator) to facilitate the reaction.

Question 3

How are polymers like spagetthi in a bowl?

Answer 3

• The polymer consists of many chains of varying length and hence molecular mass.
• These chains interact through dispersion forces and also tangle together in much the same way as a strands of spagetthi do in a bowl.

Question 4

What is the difference between HDPE and LDPE ?

Answer 4

HDPE - High density Polyethene

• Form in a predominantly linear fashion, with a relatively high molecular mass, and with little branching of the chain.

• It has high mechanical strength.
Eg. Bottles and pipes

LDPE - Low density Polyethene

• Composed of polymer molecules with a large amount of chain branching.

Eg. Plastic bags, cling wrap, soft toys.

Question 6

What happens when a functional group on two adjacent monomer molecules react?

Answer 6

A larger molecule is formed and a small, stable molecule such as water is eliminated; hence, the name condensation.

Question 7

What group does Nylon belong to?

Answer 7

Polyamides; these polymers are formed from the reaction between a dicarboxylic acid and a diamine.

Question 8

How do amino acids form condensation polymers?

Answer 8

• They have Atleast two reactive functional groups in each molecule.
• As such, these molecules can also form condensation polymers.

Question 9

How are proteins formed?

Answer 9

Polymerization of amino acids.

Question 10

Why is LDPE stronger than HDPE?

Answer 10

• Because the arrangement of branches chains in LDPE tend to be further apart.
• Whereas the arrangement of unbranched chains in HDPE allows approach of polymer chains so the chains are held together by strong dispersion forces.

Question 11

List out all the commercially important addition polymers.

Answer 11

• Poly (vinyl chloride), PVC
- pipes, cable, insulation, water tanks.

• Propylene (propene)
- rope, carpet, plastic parts for cars.

• Poly (methyl mehtacrylate)
- plexiglass, paints.

• Polystyrene
- insulation, packaging.

Question 12

What are polypeptides?

Answer 12

It combines the amino acids and ultimately when the molecular mass is high enough, proteins.

Question 13

What are Silicones?

Answer 13

Silicones are a group of polymers that are built on a backbone of silicon and oxygen atoms bonded into long chain.

Question 14

How are silicone polymers made?

Answer 14

They are made by reacting chlorosilanes with water to form silanols.

Question 15

What are some useful properties of Silicones?

Answer 15

• excellent electrical insulators
• good lubricants
• very stable to extremes of temperature
• water repellent
• non-toxic
• chemically unreactive
• flexible
• non-stick

Question 16

What is the major difference between carbon polymers and the silicones?

Answer 16

• The latter are more often liquids and retain these liquid properties over a wide range of temperatures.
• Both the carbon polymers and silicones consist of long linear chains but hydrogen bonding is not possible between most silicone chains so only dispersion forces and dipole-dipole forces are present.
• The instantaneous dipole that exists in the silicone will be weaker than the instantaneous dipole in the carbon-based polymer.

Question 17

Why are the attractive forces between silicone chains weaker than those between carbon polymer chains?

Answer 17

Because the silicon-oxygen bond is much longer than the carbon-carbon bond, so the electron in the backbone of the silicone chain are spread over a much greater volume.

Question 18

How can certain physical properties (liquids, greases, resins, rubbers) be controlled ?

Answer 18

By the appropriate use of different chlorosilanes in the polymerization reaction.

Question 19

What are cross-linked silicones?

Answer 19

They are more rigid and often used as resins or rubbers that are better insulators and have greater thermal stability that carbon-based alternatives.

Question 20

Why are animal fats and plant (vegetable) oils ?

Answer 20

They are esters.

Question 21

Why are some fat molecules called Triglycerides?

Answer 21

Because they usually contain three ester groups formed from the three alcohol groups in glycerols.

Question 22

List the several characteristics the fatty acids have in common.

Answer 22

• unbranched chains of
• 10-20 carbon atoms in the chain and almost invariably consist of an even number of carbon atoms.
• Only carboxylic acid group

Question 23

List the Types of bonds in animal and vegetable fats.

Answer 23

• Animal fats - saturated; single bonds

* Vegetable Oils - unsaturated; double bonds

Question 24

What does the strength of the dispersion forces depend on?

Answer 24

• They depend on how close the molecules can get to one another.
• When a double bond is present in one or more of the chains, the symmetrical shape of the molecule is disrupted and neighboring molecules cannot get as close as they would have if all the hydrocarbon chains were saturated.

Question 25

How does the presence of double bonds affect the hydrocarbon chains of vegetable oils?

Answer 25

• More reactive.
• The vegetable oils can undergo oxidation at the double bond and the oils becomes rancid (the double bond is broken and molecules with a foul taste and odour are produced).

Question 26

What is hydrogenation?

Answer 26

• When a hydrocarbon undergoes a reaction with a suitable catalyst, the hydrogen bond adds across the double bond and produces saturated carbon atoms.
• As a results of this hydrogenation, the oil is converted into a ‘soft solid’ with a consistency better suited to spreading and cooking than butter.

Question 27

What happens during the hydrogenation process?

Answer 27

• A carefully controlled amount of hydrogen is used as a limiting reagent.
• Not every double bond is saturated in the process, but the conditions that are used for the partial hydrogenation also result in the conversion of cis double bonds to trans double bonds when the double bond interacts with the metal catalyst during the reaction.

Question 28

How is soap formed?

Answer 28

• By hydrolyzing the water links in the triglycerides of either animal fats or vegetable oils with a strong base such as sodium hydroxide of potassium hydroxide makes soap.
• The produces of this hydrolysis reaction are glycerol and the salt of the long chain fatty acid (the soap).

Question 29

What is the general name given to this hydrolysis of triglyceride to produce glycerol and salts of fatty acids?

Answer 29

Saponification

Question 30

Explain the process d Saponification.

Answer 30

1. Boil the animal or vegetable fat with a solution or Sodium Hydroxide.
2. Add salt and the sodium salt of the fatty acid precipitates from the solution.
3. Soap is filtered and carefully purified by further washing with water.

Question 31

What is the filtrate from saponification?

Answer 31

• It is the water later from the hydrolysis that contains the glycerol (glycerol is much more polar than fatty acid).
• Glycerol is a valuable produce of the reaction and can be recovered by careful distillation under reduced pressure.

Question 32

What is an Emulsifying agent/ surfactant?

Answer 32

• It is a substance that can keep two normally immiscible substances together in the same phase.
• In simple terms, a soap is capable of keeping oil dissolved in water.

Question 33

Explain the structure of a soap molecule.

Answer 33

The polar part of the soap molecule is often referred to as the hydrophilic ‘end’ because it is soluble in water.

The non-polar part of the molecule is referred to as the hydrophobic end.

Question 34

How do soaps form the cloudy suspension?

Answer 34

When the non-polar hydrocarbon chains of the soap molecules are attracted to one another by dispersion forces while the negatively charged carboxylate ends are hydrogen bonded to the surrounding water molecules.

Question 35

How does washing dishes work?

Answer 35

• Since most grease, oil and stains that are commonly referred to as ‘dirt’ are non-polar and insoluble in water, the soap micelles are able to rearrange so that the non-polar hydrocarbon tails bury themselves in the ‘dirt’.
• With the dirt now captured in the inner region of the micelle, this dirt will behave as a polar substance and mix more readily with the polar water.
• The soap has there effectively “dissolved” the dirt.
• When the soapy water is rinsed away it takes the dirt trapped in the micelles with it, leaving a clean surface.

Question 36

Is it possible to increase the rate if the washing process?

Answer 36

Yes.

• Vigorous agitation - micelles break apart
• Warm water - soften fats & oils

Question 37

What is scum?

Answer 37

An insoluble precipitate that forms in the presence of ions such as Calcium, magnesium and iron. (Hard water)

Question 38

How is detergent different from soap?

Answer 38

• The carboxylate COO- is replaced with a sulfonate, SO3-.

* This makes it an effective surfactant ion that would not produce a scum in hard water.

Question 39

How can the manufacture of a detergent be achieved?

Answer 39

By reacting an alkyl benzene with concentrated sulfuric acid, followed by sodium hydroxide.

Question 40

What is biodiesel?

Answer 40

It is a fuel generally made by converting the fatty acids obtained from animal fats or vegetable oils into esters.

Question 41

What is the reaction with sodium hydroxide in the presence of methanol called?

Answer 41

Transesterification.