B3 food tests practical

Question 1

describe each test:

lipids

Answer 1

• use sudan III
• transfer sample to a boiling tube add a few drops od Sudan III
• posive reult is a red stain formed at surface like a ring of fat
• negative result is just acloudy mix of all reactants

Question 2

describe each test:

starch

Answer 2

• use iodine
• add sample then two drops of iodine
• looking for a colour change from brown to blue black

Question 3

describe each test;

glucose

Answer 3

• use benedicts solution
• grind food and water filter into boiling tube add 3cm cubed of benedicts solution, heat mixture above 80 degrees celcius for 3 mins
• positive result is blue to brick red

Question 4

describe each test:

protein

Answer 4

• use biuret solution
• filter mixture into a boiling tube, add 3cm cubed of buiret solution leave for 3 mins
• look for colour change from blue to purple

Question 5

a student wanted to test a sample for the presence of protein, wrte a risk assessment for this activity

Answer 5

general safety practices in labs:

• wear goggles to protect your eyes
• wash hands at the end of every practical
• clear up any spills quickly
• do not eat any of the food

what could hurt uoi in practical:
biuret reagent, irritant
glass, can break
pipette, can poke you in the eyes

prevention:

• wash hands after touching biuret reagent, do not eat in lab, and if ingested or gets into the eyes inform the teacher immediately
• if glass broken inform a teacher immediately
• point pipette downwards

Question 6

a tudent picked up solution A and added it to a sample of food, solution A was blue and turned purple after adding to the food. name solution A and identify the food present in the sample

Answer 6

solution A = biuret solution

food present = protein

Question 7

benedics test for sugar requires the solution to be heated. one way to do this is heating the test tube in a beaker of water using a bunsen burner, give an alternative method to heating the solution

Answer 7

water bath

Question 8

when testing a sample for protein in a test tube, a student found tht the top of the sample tested positive wheras the bottom did not, give a reason for this result.