Question

4. EXPERIMENT: 3ml of starch solution is placed into two test tubes (#1 and #2). Lugol's solution is

added to tube #1. Benedict's solution is added to tube #2 and the tube is incubated at 37 C degrees
for 30 minutes.
What color is seen in tube #1?
In tube #2?
Explain these results:​

Answer 1

Tube 1- blue-black colour

Tube 2- blue colour

Step-by-step explanation:

Lugol's solution was first prepared by a French Physician, Jean Guillaume August Lugol. It was formerly used as a tuberculosis therapy and it consists of iodine and potassium iodide. It is still used as medication for iodine deficiency and also as an antiseptic.

Benedict's solution is used to test for reducing sugars.

Starch is known to react with iodine to form a blue-black starch-iodide complex. Hence, when a solution of Lugol's reagent is added to the starch, a blue-black colouration is observed due to the formation of the starch iodide complex.

Starch does not react with Benedict's solution because the reducing moieties in starch are not free. When starch reacts with Benedict's solution, even at 37°C, the solution remains blue because the starch ahas not been hydrolysed in order to enable reaction with Benedict's solution.