Testing for biological molecules

What solution is used to identify reducing sugars?

Benedict’s Reagent

What colour is Benedict’s Reagent?

blue

How do you carry out the test for reducing sugars?

1. add Benedict’s Reagent to a sample

2. heat the solution in a water bath that is set to a temp of 75 degrees celcius

What will be physically present if the test for reducing sugars is positive?

A coloured precipitate

What colour would the precipitate be in a positive test for reducing sugars?

The higher the concentration of reducing sugar the further the colour cahnge goes from blue - green - yellow - orange - brick red

What is used to identify starch?

Iodine

What indicates a positive test for starch?

A colour change from brown-orange to blue-black

What is the test called to test for lipids?

The emulsion test

How is the emulsion test carried out?

shaking the test sample with ethanol until it dissolves, then pouring the substance into water

How to tell if there is lipids present during the emulsion test?

the lipids will precipitate out of the liquid and how up as a milky emulsion

What test do you carry out to test if a substance contains protein?

Biuret test

How do you carry out a Biuret test?

1. add a few drops of potassium hydroxide solution to the sample to make it alkaline

2. then add copper (II) sulfate solution (which is bright blue)

How to tell if protein i present whilst carrying out the test for it?

If there is protein the solution will turn purple, if tehre is no protein then the solution will remain blue