Question

question 5
2 pts
in the starch - acid hydrolysis experiment:
a. which reagent should test positive before starch undergoes hydrolysis (that is, with the unhydrolyzed starch solution)?
b. which reagent should test positive after starch undergoes hydrolysis (that is, with the hydrolyzed starch solution)?
a. sudan iv...b. benedicts
a. iki...b. benedicts
a. iki...b. biuret
a. orange...b. dark purple/black
a. dark purple/black...b. orange

Explanation:

Starch reacts with iodine - potassium iodide (IKI) solution to give a dark purple/black color before hydrolysis. After starch is hydrolyzed into reducing sugars (such as maltose, glucose), Benedict's reagent gives a positive test (color change from blue to orange - red depending on sugar concentration). Sudan IV is for testing lipids, Biuret is for proteins.

Answer:

A. IKI
B. Benedict's