Polymers

Question 1

Addition Polymerisation

Answer 1

Question 2

Condensation Polymerisation

Answer 2

Question 3

Terylene

Answer 3

Question 4

Nylon 6,6 - a common polyamide

Answer 4

Question 5

Kevlar- a common polyamide

Answer 5

Question 6

Hydrolysis

Answer 6

Polyesters and polyamides can be hydrolysed by acid and alkali The hydrolysis will result in the original monomers forming- although the carboxylic acid or amine group will be in salt form depending on whether the conditions are alkaline or acidic

Question 7

Intermolecular bonding between condensation polymers chains

Answer 7

Polyesters have permanent dipole forces between the Cδ+=Oδ- groups in the different chains in addition to the van der Waals forces between the chains.

Polyamides (and proteins) have hydrogen bonding between the oxygen in Cδ+=Oδ- groups and the H in the Nδ- —Hδ+ groups in the different chains in addition to the van der waals forces.

Polyamides will therefore have higher melting points than polyesters

Question 8

Disposal of Polymers Landfill

Answer 8

The most common method of disposal of waste in UK Many are now reaching capacity. European regulations will mean councils are charged much more for using landfill. Most polymers (polyalkenes) are non-biodegradable and take many years to break down. Could use more biodegradable plastics, e.g. Polyamides and cellulose and starch based polymers to improve rates of decomposition

Question 9

Disposal of Polymers

Incineration

Answer 9

Rubbish is burnt and energy produced is used to generate electricity. Some toxins can be released on incineration. Modern incinerators can burn more efficiently and most toxins and pollutants can be removed. Greenhouse gases will still be emitted though. Volume of rubbish is greatly reduced.

Question 10

Disposal of Polymers

Recycling

Answer 10

Saves raw materials- nearly all polymers are formed from compounds sourced/produced from crude oil. Saves precious resources. Polymers need collecting/ sorting- expensive process in terms of energy and manpower. Polymers can only be recycled into the same type – so careful separation needs to be done. Thermoplastic polymers can be melted down and reshaped

Question 11

General structure of an α amino acid

Answer 11

Question 12

Optical Activity of amino acids

Answer 12

All amino acids, except glycine, are chiral because there are four different groups around the C

They rotate plane polarised light.

Question 13

Zwitterions

Answer 13

The no-charge form of an amino acid never occurs. The amino acid exists as a dipolar zwitterion.

Amino acids are often solids

The ionic interaction between zwitterions explains the relatively high melting points of amino acids as opposed to the weaker hydrogen bonding that would occur in the no-charge form.

Question 14

Dipeptides

Answer 14

Dipeptides are simple combination molecules of two amino acids with one amide (peptide) link.

For any two different amino acids there are two possible combinations of the amino acids in the dipeptide.

Question 15

Hydrolysis of di-peptides/proteins

Answer 15

If proteins are heated with concentrated hydrochloric acid or concentrated strong alkalis they can be hydrolysed and split back into their constituent amino acids.

The composition of the protein molecule may then be deduced by using TLC chromatography

Question 16

: Thin-layer chromatography

Amino acids

Answer 16

a) Wearing gloves, draw a pencil line 1 cm above the bottom of a TLC plate and mark spots for each sample, equally spaced along line.
b) Use a capillary tube to add a tiny drop of each solution to a different spot and allow the plate to air dry.
c) Add solvent to a chamber or large beaker with a lid so that is no more than 1cm in depth
d) Place the TLC plate into the chamber, making sure that the level of the solvent is below the pencil line. Replace the lid to get a tight seal.
e) When the level of the solvent reaches about 1 cm from the top of the plate, remove the plate and mark the solvent level with a pencil. Allow the plate to dry in the fume cupboard.
f) Spray paper with ninhydrin and put in oven Draw around them lightly in pencil.
g) Calculate the Rf values of the observed spots

Question 17

Primary Structure of Proteins

Answer 17

Proteins are polymers made from combinations of amino acids. The amino acids are linked by peptide links, which are the amide functional group

Question 18

Secondary Structure of a Protein

Answer 18

Question 19

Tertiary Structures of Proteins

Answer 19

The tertiary structure is the folding of the secondary structure into more complex shapes. It is held in place by interactions between the R- side groups in more distant amino acids .

These can be a variety of interactions including hydrogen bonding, sulfur-sulfur bonds and ionic interactions

Hydrogen bonds could form between two serine side chains in different parts of the folded chain. (Other amino acids chains can also hydrogen bond)Ionic interactions could form between acidic amino acids such as aspartic acid and basic amino acids such as lysine.

There is a transfer of a hydrogen ion from the -COOH to the - NH2 group to form zwitterions just as in simple amino acids

Question 20

Enzymes

Answer 20

Enzymes are proteins. The active site of an enzyme is usually a hollow in the globular protein structure into which a substrate molecule can bond to the amino acid side chains through a variety of interactions including

• Hydrogen bonding
• Van der Waals forces
• Permanent dipole forces
• Ionic interactions

Only substrate molecules with the right shape and correct positions of functional groups will fit and bind to the active site- called the lock and key hypothesis

Stereospecific active site If the substrate is chiral then its likely that only one enantiomer will fit in the enzyme and so only one isomer will be catalysed

Question 21

Drugs as Enzyme Inhibitors

Answer 21

Many drugs act as an enzyme inhibitor by blocking the active site. The inhibitor will often bind to the active site strongly so stopping the substrate attaching to the enzyme. (Some Inhibitors can also attach elsewhere on the enzyme but in doing so can change the shape of the active site which also stops its effectiveness) Computers can be used to help design such drugs

Question 22

Nucleotides

Answer 22

A nucleotide is made up from a phosphate ion bonded to 2-deoxyribose which is in turn bonded to one of the four bases adenine, cytosine, guanine and thymine

Question 23

Cisplatin

Answer 23

Cisplatin can also prevent the replication of healthy cells by bonding on to healthy DNA which may lead to unwanted side effects like hair loss. Unwanted side effects can be minimised by giving cis-platin in small doses. Society needs to assess the balance between the benefits and the adverse effects of drugs, such as the anticancer drug cisplatin