[Part 3]- Required practicals 🔬

Question 1

Describe how to prepare a food sample [3]

Answer 1

• take the food sample and grind this with distilled water, using a mortar and pestle- [we want to make a paste]
• transfer the paste to a beaker, and add more distilled water- then stir this so the chemicals in the food, dissolve in the water.
• filter the solution [using a funnel lines with filter paper] to remove suspended food particles.

Question 2

What are the safety features for all food tests ?

Answer 2

• all chemicals in the food tests are potentially hazardous, therefore goggles must be worn.

Question 3

What is the food test for starch?

Hint: iodine

Answer 3

• place 2cm^3 of food solution into a test tube, and add a few drops of iodine solution.
• If starch is present, then the iodine solution will turn from orange to blue-black.
• ; if starch isn’t present, the iodine solution will stay orange.

Question 4

What is test for proteins? [Full steps]

Hint: biuret reagant

Answer 4

• take 2cm^3 of food solution and add into a test tube.
• then add 2cm^3 of biuret solution [reagant], into the test tube
• if proteins are present the biuret [reagant] solution will change from blue, to a purple or lilac colour.

Question 5

What is the test for sugars (reducing) ?

Hint: Benedict is a fat guy that loves sugar, he has so much sugar that he goes brick red, also he likes it hot.

Hint #2: Mix with water.

Answer 5

• place 2cm^3 of food solution into a test tube, then adding ten drops of Benedict’s solution.
• place the test tube containing the solution, into a beaker and half-fill the beaker, with water from a kettle- [Heat mixture/solution to 65c/75c in a water bath.]
• leave this for five minutes, and if sugars are present, the Benedict’s solution will change from blue to green/yellow/brick red

Question 5

What can you tell me about the colour of Benedict’s solution ?

Answer 5

• if sugars are present, the Benedict’s solution will change colour
• ; the colour of the Benedict’s solution gives us an approximate idea, of the amount of sugar present. [it can’t tell us the exact amount]

Question 6

What does the colour of the Benedict’s solution, tells us about the concentration of sugar ? [3]

Answer 6

• a green colour, tells us that there’s a small amount of sugar
• a yellow colour, tells us there is more sugar present
• ; a brick-red colour, tells us that there is a lot of sugar present.

Question 7

What is a key fact about the Benedict’s solution ? [3]

Answer 7

• the Benedict’s test, only works for certain sugars. For example, glucose.
• These are called reducing sugars. [they donate their electrons to other molecules]
• ; the Benedict’s test doesn’t work for non-reducing sugars such as sucrose.

Question 8

What are the safety features for the sugars food test?

Hint: test tube holder.

Answer 8

• Use a test tube holder to place in the water bath, (+ for 5 minutes leave it in the water bath.)
• Also remember to point the test tube away from you + anyone else.

Question 9

What is the test for lipids?

Hint: turns cloudy white.

Answer 9

• transfer 2cm^3 of our food solution to a test tube.
• then add a few drops of ethanol and distilled water and gently shake the solution.
• if lipids are present, then a white cloudy emulsion will form.

Question 10

What don’t we do when testing for lipids?

Answer 10

• when testing for lipids, we take the food sample and grind it with distilled water, using a mortar and pestle ; we don’t filter the solution when testing for lipids.
• That is because lipid molecules, can stick to filter paper.

Question 11

When testing for lipids, why is it important that no naked flames are present ?

Answer 11

• since ethanol is highly flammable, it’s very important that no naked flames are present.