PAG 9.2 qualitative test for lipids

Question 1

method for liquid samples

Answer 1

1) add 2cm3 of ethanol to each sample and shake throughly
2) add 2cm3 of distilled water to each sample and shake gently to mix
3) observe the appearance of each sample

Question 2

method for solid samples

Answer 2

1) add 2cm3 to each sample
2) using the glass rod, gently mash each sample
3) shake each tube throughly
4) allow the solid to settle at the bottom of the tube
5) pipette the ethanol from each sample into a fresh tube leaving the solid sediment behind
6) add 2cm3 distilled water and shake gently to mix
7) observe appearance

Question 3

explain in terms of their solubility to different solvents why you do not see false positives due to monosaccharides and disaccharides?

Answer 3

they dissolve in water so will not form an emulsion

Question 4

explain in terms of their solubility to different solvents why you do not see false positives due to starch?

Answer 4

it’s not soluble in ethanol

Question 5

explain in terms of their solubility to different solvents why you do not see false positives due to nucleic acid?

Answer 5

insoluble in ethanol and soluble in water

Question 6

explain in terms of their solubility to different solvents why you do not see false positives due to proteins?

Answer 6

insoluble in ethanol

Question 7

how could the test be made into a semi-quantitive test?

Answer 7

equal mass of each solid sample and then measure the height of each emulsion and compare

Question 8

how could the test be made into a fully quantitative test?

Answer 8

use a colorimeter