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Flashcards in Testing for carbohydrates Deck (21)
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What happens during a reduction reaction?

An electron is gained


What are reducing sugars?

any sugar that is capable of acting as a reducing agent because it has a free aldehyde group or a free ketone group.


What is the name of the chemical that you would use to test for a reducing sugar?

Benedict's reagent


What is Benedict's reagent?

An alkaline solution of copper sulfate


What are the three steps to carrying out this experiment?

  1. Place the sample to be tested in a boiling tube. *If it is not in liquid form, grind it up or blend it in water
  2. Add an equal volume of Benedict's reagent
  3. Heat the mixture gently in a boiling water bath for five minutes


What happens when a reducing sugar reacts with the Benedict's reagent?

Tye reducing sugar would react with the copper ions in the Benedict's reagent. A reduction reaction would take place and so the copper ions gain electrons. This changes them from the blue Cu2+ ions to red Cu+ ions.


What is the colour of the participate formed when a reducing sugar reacts with the Benedict's reagent?



What kind of test results are produced with this type of experiment? (i.e quantitative or qualitative)



Draw out the spectrum of colours you could expect to find in your results, along with the volume of reducing sugars likely to be present, when undergoing this experiment.

  • None- blue
  • Very low- green
  • Low- yellow
  • Medium- orange
  • High- red


What is the name of the most common non-reducing sugar?



How could you manipulate sucrose so that it gives a positive test result for the presence of reducing sugars?

First sucrose must be boiled with dilute hydrochloric acid. This means that it has been hydrolysed by the acid to form glucose and fructose (which are both reducing sugars)


The iodine test is used to detect the presence of....`



How do you carry out the iodine test?

A few drops of iodine dissolved in a potassium iodide solution is mixed with the sample.


From the results of the iodine test, how would you know if starch is present in the sample?

If the solution changes colour from yellow/brown to purple/black then starch is present in the sample.


From the results of the iodine test, how would you know if starch is not present in the sample?

If the solution remains yellow/brown


What is a reagent strip?

They can be used to test for the presence of reducing sugars (most commonly glucose)


How do the use of reagent strips provide and advantage?

The use of the colour coded chart means that the concentration of the sugar can be determined.


What is a colorimeter?

A colorimeter is an instrument which compares the amount of light getting through a solution with the amount which can get through a sample of pure solvent. Substances absorb light for a variety of reasons. Pigments absorb light at different wavelengths.


What are biosensors?

The term “biosensor” is short for “biological sensor.” The device is made up of a transducer and a biological element that may be an enzyme, an antibody or a nucleic acid. The bioelement interacts with the analyte being tested and the biological response is converted into an electrical signal by the transducer.


video on experiment practical


Animated video on the benedict's test