Benedict's Test is used for
sugar is the general term for
monosaccharides and disaccharides
Test for Reducing Sugars e.g maltose
1.Add Benedicts reagent to a sample and heat it (making sure it doesnt boil)
2.If the test is positive it will form a coloured precipitate (blue-green-yellow-orange-brick red)
3.A more accurate way of comparing the amount of reducing sugar in different solutions is to filter the solution and then weigh the precipitate.
Test for Non-Reducing Sugars e.g sucrose
1. break down into monosaccharides
2. do this by boiling the solution with dilute hydrochloric acid and then neutralisng it with sodium hydrogencarbonate.
3.Then carry out Benedicts test as you would with reducing sugars
4.If the test is positive this could mean the sugar could be reducing or non-reducing, so the reducing sugar test must also be carried out to rule out it being a reducing sugar
Iodine Test is used for
Add Iodine dissolved in potassium iodide solution to the test sample
starch present- colour changes to blue/black colour
No starch present- colour remains browny/orange
Biuret Test is used for
1. The test solution needs to be alkaline, so first a few drops of sodium hydroxide solution need to be added
2. Then copper(II) sulfate solution.
If protein is present- a purple layer forms
If no protein is present- colour remains blue
Emulsion Test is used for
1. Shake the test substance with ethanol then pour into water
If lipid is present the the solution will turn cloudy/milky
The more lipid there is the more noticeable the change will be
No Lipid- The colour will stay clear
Colorimetry is used to
determine the the concentration of a glucose solution
A device that measures the absorbance (the amount of light absorbed by the solution). The more concentrated the colour of the solution the higher the absorbance is.
A calibration curve for glucose
1.Make up several glucose solutions of different known concentrations, same volume in each
2. Benedicts test on each, use same amount of benedicts in each, enough to react with all solutions with some reagent still left over
3.remove any precipitate from solutions
4. use colorimeter to measure absorbance of the benedicts solution remaining in each tube
5. use results to make calibration curve
Then any unknown solutions concentration of glucose can be worked by the curve.