1 Biological Molecules: Benedicts test and iodine test Flashcards
(11 cards)
1
Q
What is Benedict’s reagent ?
A
- blue solution used to test for reducing + non reducing sugars
2
Q
What is the non- reducing sugar test?
A
- following a negative reducing sugar test
- heat solution in a water bath with dilute HCl to hydrolyse the non -reducing sugar into its monosaccharides by breaking the bonds
- add an alkali ( NaOH) to neutralise
- perform Benedict’s test again
- if you get a positive result after hydrolysis , non- reducing sugars are present
3
Q
What is the reducing sugar test?
A
- add excess Benedict’s reagent to the sample
- heat in a water bath
4
Q
Examples of reducing sugars:
A
- all monosaccharides
- some disaccharides = maltose and lactose
5
Q
Examples of non- reducing sugars:
A
- disaccharides or polysaccharides like sucrose
6
Q
What is the colour of Benedict’s Reagent?
A
- pale blue
7
Q
What is a positive result for the Benedict’s test ?
A
- reducing sugar present= coloured precipitate will form
- the colour of the precipitate will indicate the amount of sugar present, brick red being the highest amount
8
Q
What is the negative result for the Benedict’s test?
A
- solution stays pale blue
9
Q
Hazards and precautions of the Benedict’s test?
A
- Benedicts reagent is an irritant = wear goggles and wash with water on contact with skin, wear lab coat
- hot water can cause burns = caution when pouring/ carrying
- dilute NaOH and HCl can be corrosive = wear goggles, wash hands on contact with skin
10
Q
What quantitative result measurements can be used in the Benedict’s test?
A
- comparing precipitate colour
- filter solution and weigh precipitate
- remove precipitate and use a colorimeter to measure the absorbance remaining Benedicts solution
11
Q
What is the test for starch?
A
- add iodine
- if starch present iodine will turn from brown to blue/ black
