!! required practical 4, food tests

Question 1

why must goggles be worn during experiment

Answer 1

all chemicals used potentially hazardous

Question 2

3 steps to produce food solution

Answer 2

1. grind food solution with distilled water with a mortar and pestle, to make a paste
2. transfer paste to beaker and add more distilled water, stir so chemicals in the food dissolve into the water
3. filter solution to remove suspended food particles

Question 3

how to test for carbohydrates

Answer 3

test for starch then test for glucose

Question 4

method to test for starch

Answer 4

place 2cm cubed of food solution into a test tube

add a few drops of iodine solution (orange)

if starch is present, solution should turn from orange to blue-black

Question 5

method to test for glucose

Answer 5

place 2cm cubed of food solution into a test tube

add a few drops of benedict’s solution (blue)

place test tube into beaker half full with hot water from the kettle

leave for 5 minutes, if glucose present solution should have changed colour

colour of solution gives approx measurement of amount fo sugar in solution

green = small amount of sugar present

yellow = little more

brick red = lot more sugar present

Question 6

what type of sugar can benedict’s solution test

Answer 6

reducing sugars, e.g glucose

Question 7

method to test for protein

Answer 7

place 2cm cubed of food solution into a test tube

add a 2cm cubed of biuret solution (blue)

is protein present goes purple / lillac

Question 8

method to test for lipids

Answer 8

(don’t filter)

place 2cm cubed of food solution into a test tube

add a few drops of distilled water and ethanol.

gently shake solution

if lipids are present then white cloudy emulsion forms

Question 9

why do you not filter lipid solution

risk of lipid food test

Answer 9

lipid molecules can stick to filter paper

ethanol highly flammable, no naked flames should be present