Tests for starch, glucose, protein and lipids

Question 1

what is used to test for starch?

Answer 1

iodine

Question 2

describe the procedure of test for starch

Answer 2

• add drop of starch to depression in spotting tile using pipette
• add drop of iodine

Question 3

what colour change occurs in test for starch?

Answer 3

orangey-brown to blue-black (starch-polyiodide complex)

Question 4

what is used to test for reducing sugars?

Answer 4

benedict’s solution

Question 5

describe procedure of test for reducing sugar

Answer 5

• add 10cm3 of glucose solution to test tube
• add few drops of benedict’s
• heat in water bath for 5m

Question 6

what colour change occurs in test for reducing sugars?

Answer 6

bright blue to brick red

Question 7

why will the solution turn brick red in reducing sugars test?

Answer 7

• cu 2+ions reduced to cu+ ions

- cu+ ions form copper oxide in presence of sodium hydroxide

Question 8

what is done first to a non-reducing sugar before it is tested using benedict’s?

Answer 8

• boiled in hydrochloric acid for 15mins to break glycosidic bonds - ACID HYDROLYSIS
• neutralised with sodium hydroxide because benedict’s requires alkaline medium

Question 9

what is the name for the test for lipids?

Answer 9

emulsion test

Question 10

describe the procedure of test for lipids

Answer 10

• add drop of oil to test tube
• add 5cm3 of ethanol and shake to dissolve oil
• pour mixture into test tube filled 3/4 with water

Question 11

what is observed during emulsion test

Answer 11

milky white emulsion formed on surface of water

Question 12

what is used to test for proteins?

Answer 12

biuret reagent

Question 13

describe the procedure of test for proteins

Answer 13

• add 5cm3 of protein solution to test tube

- add equal volume of biuret

Question 14

what colour change occurs in test for proteins?

Answer 14

pale blue to lilac (mauve) solution