organic materials

Question 1

amino acid ‘R-group’ properties

(side chain)

Answer 1

polar (OH) / non-polar (CH₃)

proton donor (COOH) / proton acceptor (NH₂)

Question 2

acid-base properties of amino acids

Answer 2

di-functional from NH₂ & COOH

∴ amphoteric depending on pH of the solution environment

NH₂ → NH₃⁺ & COOH → COO⁻

Question 3

zwitterion in solution

(dipolar ion)

Answer 3

overall neutral amino acid containing both positive & negative change

present at isoelectric point (pH)

Question 4

amino acid in low pH (pH < pI)

Answer 4

zwitterion + abundance of H₃O⁺ → cation + H₂O

Question 5

amino acid in high pH (pH > pI)

Answer 5

zwitterion + abundance of OH¯ → anion + H₂O

Question 6

condensation polymerization reaction of 2-amino acids (α-amino acids)

Answer 6

NH₂ & COOH react together to form a peptide (amide) link (CONH) + H₂O

Question 7

N-terminal amino acid

Answer 7

end of the polypeptide chain with a free amino group

Question 8

C-terminal amino acid

Answer 8

end of the polypeptide chain with a free carboxyl group

Question 9

primary structure of protein

Answer 9

sequence of amino acids joined by covalent peptide bonds

Question 10

secondary structure of protein

Answer 10

hydrogen bonding between N-H & C=O causes folding into α-helices (polypeptide coils into a spiral) or β-pleated sheets (polypeptide folds into parallel layers)

Question 11

tertiary structure of protein

Answer 11

3D shape formed through forces between R-groups of amino acids

e.g. covalent disulfide bridge (S-S) & ionic salt bridge (NH₃⁺/COO⁻)

(hydrogen bonding, dipole-dipole attraction, dispersion forces)

interial hydrophobic & exterial hydrophilic R-groups

Question 12

quarternary structure of protein

Answer 12

multiple polypeptide chains (& sometimes non-protein molecules) form large complex functional units held together by dispersion forces

(e.g. haemoglobin)

hydrogen bonding, dipole-dipole attraction & ionic interactions may also be present

Question 13

characteristics of biological enzymes

Answer 13

proteins that catalyze biochemical reactions by providing an alternate reaction pathway with lower activation energy

sensitive as changes in temperature or pH may disrupt the forces that determine their tertiary structure

active sites are substrate specific

Question 14

describe the effect of changing temperature/pH on an enzyme ?

Answer 14

enzymes are are temperature/pH specific

changes can disrupt the forces that determine their tertiary structure

active sites no longer binds to the substrate

Question 15

triglycerides

Answer 15

condensation reaction between glycerol (propane-1,2,3-triol) & 3 fatty acids

OH (glycerol) + COOH (fatty acid) → ester link (COO) + H₂O

Question 16

saturated fatty acids

Answer 16

hydrocarbon chains with only C-C bonds

Question 17

unsaturated fatty acids

Answer 17

monosaturated : hydrocarbon chains with one C=C bond

polysaturated : hydrocarbon chains with multiple C=C bonds

Question 18

omega & alpha carbons

Answer 18

omega : last carbon furthest away from COOH

alpha : first carbon within COOH

Question 19

melting point of triglycerides

Answer 19

↑chain length = ↑melting point

∵ ↑dispersion forces

↑C=C bonds = ↓melting point

∵ cis-arrangement bends the hydrocarbon chain

∴ ↓dispersion forces (fatty acids cannot pack tightly)

Question 20

saponification (hydrolysis)

Answer 20

triglyceride + 3NaOH → glycerol + 3 fatty acid-COO⁻Na⁺ (soap)

Question 21

soap as a medium between water & oil

Answer 21

charged COO⁻Na⁺ (hydrophilic) forms ion-dipole bonding with H₂O

non-polar hydrocarbon tail (hydrophobic) forms weak dispersion forces with oil

Question 22

soap in water

Answer 22

soap clumps together to form a spherical micelle

hydrophilic ends (charged carboxylate group) face outwards & hydrophobic ends (non-polar hydrocarbon tail) face inwards

Question 23

cleaning action of soap

Answer 23

agitation (washing) breaks the micelle & non-polar ends attach to the oil

ion-dipole bonding with water lifts the oil particles & non-polar ends surround the oil molecules to trap them (forming a micelle again)

Question 24

soap in hard water

Answer 24

hard water contains metal ions (e.g. Mg²⁺, Ca²⁺) which react with soap (sodium stearate)

this creates magnesium/calcium stearates, which are insoluble in water

∴ poorly washed clothes & soap scum

Question 25

glucose in solution

Answer 25

α-glucose (cyclic) : OH group on C₁ points down β-glucose (cyclic) : OH group on C₁ points up

Question 26

aldose vs ketose

Answer 26

glucose : aldose (terminal C=O) fructose : ketose (non-terminal C=O)

Question 27

disaccharides

Answer 27

condensation reaction between two monosaccharides' OH groups (C₁ - C₄) glycosidic bond (C₁-O-H + H-O-C₄ → C₁-O-C₄ + H₂O) e. g. glucose + glucose → maltose + H₂O e. g. glucose + fructose → sucrose + H₂O e. g. glucose + galactose → lactose + H₂O | (C₁ loses H & C₄ loses OH)

Question 28

starch (amylose)

Answer 28

linear glucose polymer with α-1,4-glycosidic bonds

Question 29

starch (amylopectin)

Answer 29

branched glucose polymer with α-1,4-glycosidic bonds & α-1,6-glycosidic bonds

Question 30

cellulose

Answer 30

linear glucose polymer with β-1,4-glycosidic bonds

Question 31

amorphous regions

Answer 31

tangled arrangement of polymer chains ∴ weaker intermolecular forces

Question 32

crystalline regions

Answer 32

ordered arrangement of polymer chains ∴ stronger intermolecular forces

Question 33

low-density polyethene

Answer 33

created under high pressure & temperature; contains many disordered branches ∴ amorphous ∵ molecules cannot pack tightly (weak dispersion forces) | (low melting point, low density, soft)

Question 34

high-density polyethene

Answer 34

created under low pressure & a transition metal catalyst; contains few ordered branches ∴ crystalline ∵ molecules pack tightly (strong dispersion forces) | (high melting point, high density, hard)

Question 35

isotactic polypropene

Answer 35

regularly arranged methyl side groups all on one side of the polymer chain ∴ semi-crystalline

Question 36

atactic polypropene

Answer 36

randomly arranged methyl side groups on either side of the polymer chain ∴ amorphous

Question 37

syndiotactic polypropene

Answer 37

regularly arranged methyl side groups on alternating sides of the polymer chain ∴ crystalline

Question 38

polytetrafluoroethene

Answer 38

↑melting point from strong C-C & C-F bonds non-polar from symmetrical nature (although dipoles are present) chemically inert from fluorine atom coating | (insoluble & non-stick)

Question 39

polyester

Answer 39

condensation reaction between a di-ol & di-oic acid ester link + H₂O | (e.g. PET) ## Footnote co-polymer

Question 40

advantages & disadvantages of polymers

Answer 40

advantages : mechanical strength; low density; generally chemically resistant disadvantages : derived from non-renewables; not biodegradable; toxic when burnt