Mini Practicals Flashcards
What is the Biochemical food test for reducing sugars:
(Give positive and negative result)
• place 1cm^3 of sample in a test tube
• add 1cm^3 of Benedict’s solution
• heat at 80C in a water bath
Positive = brick red precipitate
Negative = blue
What is the Biochemical food test for non- reducing sugars:
(Give positive and negative result)
Do reducing sugar test first - if negative then test for non reducing sugar:
• place 1cm^3 of sample in a test tube
• add 5 drops of HCL (acid)
• Boilfor 3 mins in a water bath
• Neutralise with 5 drops of NaOH
• Add 1cm^3 Benedict’s solution
• heat at 80C for 5 mins in a water bath
Positive = brick red precipitate
Negative = blue
What is the Biochemical food test for starch:
(Give positive and negative result)
• place 1cm^3 of sample in a test tube
• Add 3 drops of iodine and shake gently
Positive = blue-black
Negative = orange/brown
What is the Biochemical food test for protein:
(Give positive and negative result)
• place 1cm^3 of sample in a test tube
• Add 1cm^3 of Biuret solution
Positive = Purple
Negative = Pale blue
What is the Biochemical food test for Lipids:
(Give positive and negative result)
• place 1cm^3 of sample in a test tube
• Add 1cm^3 of ethanol
• Shake
• Add a few drops of water
• Shake
Positive = white emulsion
Negative = colourless
What is the method for determining glucose concentration quantitatively?
What are 2 alternative methods for measuring glucose concentration?
Method 1 - filtering and weighing
After filtering collect the precipitate, dry it and weigh. The more mass the precipitate has, the more glucose in the solution. You would need to zero the scales with the weighing paper before weighing it
Method 2 - filtering and colorimeter
After filtering , colorimeter the solutions. If more precipitate had been made in the reaction, more of the Benedict’s has been reacted and removed, leaving behind a paler solution. If this was put in a colorimeter, you would get a lower absorbance reading. Lower absorbance = more glucose
(Would give a negative correlation on a graph)
CHROMATOGRAPHY
What is the method for chromatography of amino acids?
How do you calculate an Rf value?
What is capillary action of amino acids?
How the amino acids move up the stationary phase (chromatography paper). Those with the least mass move further up - those with greater mass are deposited closer to the origin.
What are the precautions for chromatography?
• Wear eye protection
• use plastic gloves and work on a clean surface as chromatography paper must not be touched with hands
Why do we spray ninhydrin on the paper?
Amino acids have no colour. Therefore all of the procedures need to be carried out “blind” and the results can only be seen when a revealing agent (ninhydrin) is sprayed on the results
Can you have an Rf value greater than 1?
No because the solvent is what moves the solute
Why was it important to keep the lid on the tank?
Solvent is volatile and therefore evaporates very quickly. The atmosphere in the tank is saturated with the solvent do that the solvent can rise up through the stationary phase.
