[Part 3]- Required practicals 🔬 Flashcards
Describe how to prepare a food sample [3]
- 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.
What are the safety features for all food tests ?
- all chemicals in the food tests are potentially hazardous, therefore goggles must be worn.
What is the food test for starch?
Hint: iodine
- 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.
What is test for proteins? [Full steps]
Hint: biuret reagant
- 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.
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.
- 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
What can you tell me about the colour of Benedict’s solution ?
- 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]
What does the colour of the Benedict’s solution, tells us about the concentration of sugar ? [3]
- 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.
What is a key fact about the Benedict’s solution ? [3]
- 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.
What are the safety features for the sugars food test?
Hint: test tube holder.
- 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.
What is the test for lipids?
Hint: turns cloudy white.
- 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.
What don’t we do when testing for lipids?
- 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.
When testing for lipids, why is it important that no naked flames are present ?
- since ethanol is highly flammable, it’s very important that no naked flames are present.
