Question

question 7
why can the benedicts test not detect disaccharides?
because there is no acid present in disaccharides
because disaccharides do not taste sweet enough
because disaccharides do not contain a carbonyl group with a double bond
because disaccharides do not contain any water

question 8
0.25 pts
think of the procedure for the hydrolysis of sucrose, answer the following question: after the hydrolysis process, which of the tubes, a, b or c, will contain molecules that can turn the benedicts solution red?
a = sucrose + hcl
b = sucrose + water
c = water + hcl
c
a
b
a and c

question 9
0.2 pts
what molecule will test positive in the iodine assay?
starch
protein
glucose
sucrose

Explanation:

• Question 7: Benedict's test detects reducing sugars which have a free - aldehyde or ketone (carbonyl) group. Most disaccharides lack a free carbonyl group with a double bond in their structure, so they don't react with Benedict's solution.
• Question 8: Sucrose hydrolyzes in the presence of an acid (HCl in tube A) to form glucose and fructose, both of which are reducing sugars and can turn Benedict's solution red. Tubes B and C do not have the necessary reaction to produce reducing sugars.
• Question 9: Iodine assay is used to detect starch. Starch forms a blue - black complex with iodine, while proteins, glucose, and sucrose do not give this positive reaction with iodine.

Answer:

Question 7: because disaccharides do not contain a carbonyl group with a double bond
Question 8: A
Question 9: starch