2.1 : testing for biological molecules

Question 1

testing for non reducing sugars: sucrose

Answer 1

1. add HCL
2. boil 2-3 min
3. neutralise with alkali until no bubbles form
4. add Benedict
5. heat to 60-80C for 5 minutes
   - glycosidic bond can’t react: acid breaks it

Question 2

testing for starch

Answer 2

• iodine solution : orange/brown to blue/black

Question 3

testing for reducing sugars

Answer 3

• Benedict: blue to red
• heat, 80C
• semi quantitative test
• green - yellow - orange - red

Question 4

biuret test: testing for proteins

Answer 4

1. add protein
2. add NaOH
3. drops of CuSO4
   - light blue to purple/violet

Question 5

cloudy emulsion: testing for lipids

Answer 5

1. mix with ethanol
2. add to water
   - white emulsion