CD 6, 7, 8

Question 1

describe acid dyes and their bonding

Answer 1

• they have a negative charge when dissolved in water due to the presence of sulfonate groups
• applied in acid conditions to fibres, so polyamide and protein fibres will have a positive NH3 + groups

Question 2

describe the two strategies for covalent bonding in dye molecules and fibres

Answer 2

• mordanting

males a metal ion join the dye to fabric, groups on the fabric and dye make dative covalent bonds to central metal to form a chelate complex ion
metal ions used at morants Al3+ / Cr3+

• Fibre-reactive dyes

make use of a reactive group attached to the dye molecule to form a bridge between the dye and fibre

Question 3

define chelate

Answer 3

a complex ion in which the metal ion is bonded to two or more atoms in the same molecule

Question 4

describe hydrogen bonding in dyes

Answer 4

• cotton / cellulose contain a large amount of OH- groups
• dye molecule would contain amine groups or alcohol groups
• hydrogen bonding is not broken in the presence of water
• dye molecules usually linear, attaches in several places

Question 5

Describe instantaneous dipole - induced dipole bonding in dyes

Answer 5

• known as disperse dyes
• have very few polar groups, so NOT soluble in water
• dyes are suspended in water, small dye molecules diffuse into fabric and are held by ID-ID bonds between dye and fabric

Question 6

fabric dyes that make ionic bonds

Answer 6

nylon, wool, silk

Question 7

fabric that makes hydrogen bonds

Answer 7

cotton

Question 8

fabric that makes ID-ID bonds

Answer 8

polyester

Question 9

define triglyceride

Answer 9

an ester molecule formed by the reaction of one molecule of glycerol (propan 1, 2, 3-triol) and three fatty acids molecules

Question 10

difference between oils and fats

Answer 10

• oils are liquid at room temperature
• fats are solid

Question 11

solubility of fats and oils

Answer 11

• the presence of long chain non-polar fatty acid chains in fats and oils ensures the substances do not mix with water

Question 12

how do you know if a triglyceride is saturated or unsaturated, which is E and which is Z

Answer 12

• saturated will only contain straight chain carboxylic acids E
• unsaturated will be bent all over the place and will have carbon-carbon double bonds Z

Question 13

By looking at two triglycerides, how do you know which is a fat and which one is an oil, explain why

Answer 13

• Saturated triglycerides are fats because the molecules can pack closely together, so the attractive bonds between the molecule will be stronger
• unsaturated triglycerides are oils because the C-C double bonds cause kinks in the molecule that do not allow them to pack together closely, so the attractive bonds within the molecule will be weaker, so the molecule is more likely to be a liquid

Question 14

how to convert oils to fats

Answer 14

hydrogenation
reduces the number of double bonds and allows it to become more saturated
partially hydrogenated because it will still contain one or two double bonds

Question 15

what are the stationary and mobile phases in GLC

Answer 15

• the mobile phase is an unreactive gas, such as nitrogen, the carrier gas
• the stationary phase is a small amount of liquid with a high boiling point, held on a finely divided inert porous solid

Question 16

what is the apparatus for GLC called

Answer 16

gas-liquid chromatograph

Question 17

how does GLC work

Answer 17

• you must calibrate GLC instrument using samples of known compounds and keep conditions constant throughout the analysis
• sample is injected into gas stream, components are carried through the mixture in a stream of gas
• each components distributes itself differently between the two phases (liquid and gas), so emerges from the column at different times
• compounds that favour mobile phase emerge first (volatile liquids)
  -compounds that favous stationary phase and dissolve in the liquid will emerge last and have a greater affinity for stationary phase

Question 18

how to calculate the partition coefficient

Answer 18

K pc = component in stationary phase / component in mobile phase
- the greater the partition coefficient, the greater affinity the sample has for the stationary phase

Question 19

how are the components detected

Answer 19

• detector on the outlet monitors the compounds coming out of the column, signals are plotted out by a recorder on a chromatogram.
• chromatogram is recorder response against time

Question 20

what is the retention time

Answer 20

• the time that a compound is held in a column, under given conditions is characteristic of a compound

Question 21

why does the area under each peak differ

Answer 21

• it depends on the amount of compound present
• gas chromatogram can be used to work out the relative amount of each compound in a mixture