Practical Flashcards
What is Biuret’s test for
Proteins
What is Benedict’s test for
Reducing sugar
What is Iodine test for
Starch
What is ethanol emulsion test for
Fats
How to carry out Biuret’s test
- Add 1cm^1 of sodium hydroxide solution to 2cm^3 of food solution
- Shake thoroughly
- Add 1% copper(II)sulfate solution drop by drop, shaking after each drop until colour change observed
How to carry out iodine test
- Place food substance or solid food onto white tile
- Add a few drops of iodine solution to substance and observe colour change
How to carry out Benedict’s test
- Add equal volume of Benedict’s solution to 2cm^3 of food solution in a test tube
- Shake mixture thoroughly
- Place test tube in a boiling water bath for 5 minutes
- Observe precipitate formation and colour changes
How to carry out ethanol emulsion test
- Add 2cm^3 of ethanol to 2cm^3 of food solution in a test tube
- Shake mixture thoroughly
- Decant ethanol mixture into another test tube containing 2cm^3 of water
Observations and conclusions if no reducing sugars present
- Solution remained blue
- No reducing sugars present
Observations and conclusions if little concentration of reducing sugars present
- Green precipitate formed
- Little concentration of reducing sugars present
Observations and conclusions if moderate concentration of reducing sugars present
- Yellow precipitate formed
- Moderate concentration of reducing sugars present
Observations and conclusions if large concentration of reducing sugars present
- Orange or brick-red precipitate formed
- Large concentration of reducing sugars present
Observations and conclusions if proteins present
- Violet colouration observed
- Proteins present
Observations and conclusions if proteins absent
- Solution remained blue
- Proteins absent
Observations and conclusions if starch present
- Blue black colouration observed
- Starch present
Observations and conclusions if starch absent
- Solution remained brown
- Starch absent
Observations and conclusions if fats present
- White emulsion formed
- Fats present
Observations and conclusions if fats absent
- Solution remained colourless
- Fats absent
How to increase reliability of an experiment
Repeat experiment a few more times and find the average values
How to increase accuracy of experiment
Use more accurate apparatus
Graph plotting is what against what
Plot a graph of y against x
Things to do for planning exercise
- Identify aim of experiment
- Identify independent, dependent, and constant variables
- Specify at least 5 different, regular intervals for independent variable
- Specify what graph to plot
Conclusions: - If what happens, then what happens (Relate back to aim of experiment)
