test for reducing sugars Flashcards
what is the name of the test for reducing sugars?
benedict’s test
what do reducing sugars do?
give electrons
what does benedict’s solution contain?
Cu+2 ions which make the solution blue
what are examples of reducing sugars?
all monosaccharides and disaccharides except sucrose
explain the process of the benedict’s test
- add a small amount (2cm^3) of the sample into a test tube with 2cm^3 of benedict’s solution
- heat in a water bath for 5 minutes
- brick red or orange colour is a positive result and a reducing sugar is present
- if benedict’s solution remains blue , no reducing sugar is present and this is a negative result
what state must the sample be in before the benedict’s test is carried out?
it must be a liquid
what is the order of colours of the solution from highest concentration of reducing sugar to lowest concentration of reducing sugar?
red, orange, yellow, green
what are the controlled variables of this test?
- same volume of benedict’s solution and the same volume of test solutions
- samples must be heated for the same amount of time
- samples must be heated at the same temperature
how to accurately compare the colour intensity produced?
with a colorimeter
how do you use a colorimeter?
- set up colorimeter to absorb a particular wavelength of light
- calibrate the colorimeter (set the zero concentration mark by measuring the absorbance of a sample of distilled water)
- measure the absorbency of solutions with a known concentration
- produce a calibration curve
- place the solution of an unknown concentration of reducing sugar in the colorimeter
- measure the absorbency and use the calibration curve to determine the concentration