ch 3 Biological molecule testing PAG9

Question 1

What is the two test for sugars? and what is interpreted as positive and negative?

Answer 1

Benedict’s test for reducing and
non-reducing sugars:

non reducing
1. Add dilute HCl.
2. Put in a water bath
brought to a boil.
3. Neutralise with
sodium hydrogen
carbonate.
4. Do Benedict’s Test
for reducing sugars.

Positive:Sample goes from blue (to
green to yellow to orange)
to brick red precipitate,
depending on the
concentration

Reducing:
1. Add Benedict’s
reagent to a sample and
heart in a water bath
that’s brought to a boil.

positive: Sample goes from blue (to
green to yellow to orange)
to brick red precipitate,
depending on the
concentration.

Question 2

What is the test for proteins? and what is interpreted as positive and negative?

Answer 2

Biuret test:
1. Add sodium
hydroxide solution.
2. Add copper (II)
sulphate solution.

Positive: blue-> purple

Question 3

What is the test for starch

Answer 3

Iodine test:
Add iodine in
potassium iodide
solution.

positive: brow/orange->blue-black

Question 4

What is the test for lipids?

Answer 4

Emulsions test:
1. Add ethanol.
2. Pour solution into
water.

positive: solution goes milky