1.2-1.3Carbohydrates Flashcards
Large molecules often contain carbon. Explain why this is.
Carbon atoms readily form bond with other carbon atoms ( this allows a sequence of carbon atoms of various lengths to be built up. This forms a “backbone” which other molecules can be attached )
What is a Reducing Sugars
Reduction is a chemical reaction involving the gain of electrons or hydrogen. Therefore a reducing sugar is a sugar which donates electrons to another chemical ( it can reduce).
What is the test for reducing sugars
Add 2cm3 of the food sample to be tested in a test tubes, if the sample is not in liquid form, grind it up with water
Add an equal volume of Benedictus Reagent
Heat the mixture in a gently boiling water bath for five minutes
A positive presence of a r. Sugar will turn into he solution orange-brown
Why does Benedictus Reagent turn red/orange when heated with a reducing sugar?
Sugar donates electrons that reduce blue Copper (II) sulfate into orange copper (I) oxide
Suggest a different way in which difference conc. of reducing sugars could be estimated
Dry the precipitate in each sample and weight it.
The heavier the more reducing sugar is present
What is a condensation reaction?
It is when monosaccharides join where a molecule of water is removed, so there is a disaccharide and water.
A glycosidic bond is formed
What is hydrolysis
It is the addition of water which causes a the glycosidic bond of a disaccharide to break releasing it so it’s constituting monosaccharides.
What is the test for non-reducing sugars
If sample is not already in liquid form, first ground it up in water
Add 2cm^3 of the food sample being tested to 2cm^3 of Benedictus Reagent
Place test the in gently boiling water bath for five minutes, if it does not change colour a reducing sugar is not present.
Add 2cm^3 of food sample to dilute hydrochloric Acid ( HCl) and put in a gently boiling water bath. The NaCl will hydrolyse any disaccharide present
Add NaOH ( sodium hydrocarbonate) to the test tube to neutralise the HCL. Test with pH paper to ensure its alkaline
Re-test the resulting solution with b.reagent
It will ow turn orange brown
What is a polysaccharide
It is a polymer formed by combing together many monosaccharides molecules.
Very large insoluble molecules, making them suitable for storage.
What is the test for starch?
Place 2cm^3 of the sample being tested
Add 2 drops of iodine solution and shake or stir
Presence of starch is indicated by a blue-black coloration
To hydrolyse a disaccharide it can be boiled with HCl but if hydrolysis is carried out by an enzyme a much lower temperature is required, Why?
Enzymes denature at high temperatures and this stops them from functioning therefore a Lowe temperature is required
