biochemical tests

Question 1

Describe the test for lipids

Answer 1

(Crush)
Add ethanol and mix
Then add water and mix
- Positive result: cloudy white emulsion

Question 2

Describe the test for proteins

Answer 2

Add Biuret reagent (copper sulfate & sodium hydroxide)
- Positive result: turns purple
- Negative result: stays blue

Question 3

Describe the reducing sugar test

Answer 3

Add Benedicts solution (copper sulfate and sodium hydroxide)
Add heat
- Positive result: turns red
- Negative result: stays blue

Question 4

Describe the test for non reducing sugars

Answer 4

• Add Benedicts solution and if negative result (stays blue)
• Add hydrochloric acid and BOIL (/heat)
• Then add sodium hydrogen carbonate until it stops bubbling (CO2) to neutralise
• Re-test with Benedicts reagent and heat
• Positive result: turns red/orange/yellow/green
• Negative result: stays blue

Question 5

Describe the test for starch

Answer 5

Add iodine solution / potassium iodide
- Positive result: turns blue black
- Negative result: stays yellow/brown

Question 6

The Benedicts reducing/non reducing sugar test is ____- q_______

Answer 6

Semi-quantitative