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Flashcards in Food tests - practical Deck (16)
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1
Q

what is used to test for starch in food

A

iodine

2
Q

equipment for starch test

A

food sample
test tube
iodine solution (0.01 mol/dm3)
pipettes

3
Q

method for starch test

A
  1. put some of the food sample into a test tube
  2. add a few drops of iodine solution to the food sample using a pipette
  3. if starch is present, solution turns from brown to blue-black. note any colour change in a table of results
4
Q

used to test for reducing sugars in food

A

Benedict’s solution

5
Q

equipment for reducing sugars

A
food sample
test tube
benedict's solution
hot water bath
thermometer
pipettes
6
Q

method for reducing sugars

A
  1. add equal volume or excess of benedict’s solution to the food sample in a test tube
  2. place in a hot water bath for a few minutes
  3. if reducing sugar is present, a brick red precipitate is formed. if absent, solution remains blue
    note any colour change in a table of results
7
Q

what is used to test for protein in food

A

biuret solution

8
Q

equipment for protein test

A

test tube
10cm3 measuring cylinder
biuret solution

9
Q

method to test for protein

A
  1. add a few drops of biuret’s reagent (sodium hydroxide and copper (II) sulphate) to the food sample in a test tube
  2. shake the solution to mix and wait for a a few minutes
  3. if protein is present, the solution turns from blue to purple
10
Q

what is used to test for lipids in food

A

ethanol

11
Q

equipment for lipid testing

A

food sample
test tube
ethanol
distilled water

12
Q

method for lipid testing

A
  1. add a few cm3 of ethanol to the food sample
  2. pour this mixture into a test tube of equal volumes of distilled water
  3. if lipids are present, a white emulsion is formed on the surface of the mixture
  4. this is called the emulsion test
13
Q

sources of error in these tests

A

colour change of benedict’s test and biuret test may be subtle and difficult to judge if the concentration of the tested molecule is low

14
Q

safety precaution for benedict’s test

A

tie hair back and wear safety goggles when using a bunsen burner and hot water bath

15
Q

safety precaution for biuret test

A

contains copper sulphate which is poisonous and sodium hydroxide is corrosive

wash immediately if it comes into contact with skin and wipe any spills to surfaces

16
Q

safety precaution for enthanol

A

keep ethanol solution away from flames as ethanol is highly flammable