Biochemistry Laboratory Experiment - Student Answer Sheet (Middle School
Level)
1. Molisch Test Reaction Steps:
- When sugar is mixed with strong acid, it changes into furfural.
- Furfural reacts with alpha-naphthol (Molisch reagent).
- A purple ring shows up, meaning carbohydrates are present.
2. Example of protein structure giving positive Molisch test:
- Glycoproteins, because they have sugar parts attached to them.
3a. Fehling's Test Reaction:
- Reducing sugars like glucose change blue copper ions (Cu2+) into red copper oxide (Cu2O).
- Reaction: Sugar with aldehyde group + Cu2+ -> acid + Cu2O (red solid).
3b. Function of tartrate in Fehling's test:
- Tartrate keeps copper ions dissolved in the alkaline solution so they don't form unwanted solids.
5. Barfoed's Test Reaction:
- Monosaccharides (simple sugars) reduce copper ions in acidic solution to red Cu2O quickly.
- Disaccharides react slower.
6a. Seliwanoff's Test Reaction:
- Ketose sugars (like fructose) dehydrate faster in strong acid.
- They react with resorcinol to make a red color.
6b. Function of resorcinol:
- It reacts with the dehydrated sugar to make the red color.
6c. Aim of strong acid:
- The acid helps remove water from the sugar to form furfural, which then reacts with resorcinol.
