3.4 Testing for carbohydrates

Question 1

what is Benedict’s reagent

Answer 1

copper (II) sulfate alkaline solution

Question 2

what are reducing sugars

Answer 2

all monosaccharides

some disaccharides (lactose/maltose)

Question 3

Benedict’s test for reducing sugars

Answer 3

1) place sample in boiling tube (l)
2) add equal volume of Benedict’s reagent
3) heat for 5 minutes

reducing sugars react with copper ions (reduce them) and form brick red precipitate

Question 4

Benedict’s test for non-reducing sugars

Answer 4

1. boil with dilute HCl (will get hydrolysed to 2 monosaccharides)
2. do Benedict’s test for reducing sugars

Question 5

Iodine test for starch

Answer 5

1. few drops of iodine dissolved in potassium iodide solution are mixed with sample

if starch is present = yellow brown —> purple/black

Question 6

Reagent strips

Answer 6

• used to test for reducing sugars

- can determine concentration due to colour-coded chart

Question 7

why is colorimetry used

Answer 7

• allows you to estimate glucose in solution by measuring absorbance/ transmission of light
• more concentrated solution = higher absorbance/less transmission

Question 8

how does a colorimeter work

Answer 8

1. place filter in colorimeter
2. calibrate with distilled water
3. Benedict’s test done on solution
4. filter to remove precipitate
5. % transmission is measured
6. used to plot calibration curve

Question 9

why are biosensors used

Answer 9

to find the presence and concentration of molecules like glucose

Question 10

how do biosensors work

Answer 10

1. molecular recognition = protein/strand of DNA is immobilised to surface which will interact or bind to molecule
2. transduction = transducer detects changes and produces response
3. display = produces visible signal