Sugars

• What is the general term for monosaccharides and disaccharides?


  Sugars
• What are monosaccharides?


  The simplest sugars and building blocks of carbohydrates
• What elements do all carbohydrates contain?


  C, H, and O
• What are examples of monosaccharides?


  Glucose, fructose, and galactose
• What type of sugar is glucose classified as?


  A hexose sugar
• How many carbon atoms are in a glucose molecule?


  Six
• What are the two types of glucose?

  Alpha (α) and beta (β) glucose
• What are isomers?


  Molecules with the same molecular formula but different structures
• What forms a disaccharide?


  Two monosaccharides joining together
• How are monosaccharides joined together?


  By condensation reactions
• What type of bond forms between two monosaccharides?


  A glycosidic bond
• What is released during the formation of a disaccharide?


  A molecule of water
• What disaccharide is formed from two glucose molecules?


  Maltose
• What is sucrose formed from?


  A glucose molecule and a fructose molecule
• What is lactose formed from?


  A glucose molecule and a galactose molecule
• What is the Benedict's test used for?


  To test for reducing and non-reducing sugars
• What are the two classifications of sugars?

  Reducing sugars and non-reducing sugars
• What is the appearance of Benedict's reagent before testing?


  Blue
• What happens to the sample if a reducing sugar is present during the Benedict's test?


  It forms a coloured precipitate
• How does the color change in the Benedict's test indicate the concentration of reducing sugar?


  The higher the concentration, the further the color change goes
• What is the first step to test for non-reducing sugars?


  Break them down into monosaccharides
• What is added to the sample to break down non-reducing sugars?

  Dilute hydrochloric acid
• What must be done after heating the sample with dilute hydrochloric acid?


  Neutralise it by adding sodium hydrogencarbonate
• What is the final step in testing for non-reducing sugars?

  Carry out the Benedict's test
• What are the steps in the Benedict's test for reducing sugars?


  1. Heat sample with Benedict’s reagent.
  2. Observe color change:

  • Blue: no reducing sugar present
  • Green → Yellow → Orange → Brick Red: reducing sugar present
• What are the steps in the Benedict's test for non-reducing sugars?


  1. Heat a new sample with dilute hydrochloric acid.
  2. Neutralise with sodium hydrogencarbonate.
  3. Heat sample with Benedict’s reagent.
  4. Observe color change:

  • Blue: no non-reducing or reducing sugar present
  • Green → Yellow → Orange → Brick Red: non-reducing sugar present
• What color indicates a positive result in the Benedict's test?


  Brick red
• What color indicates a negative result in the Benedict's test?


  Blue
• What should you do if the substance to be tested is a solid?


  Prepare a solution of it before heating
• Why should you always use an excess of Benedict's solution?


  To ensure that all the sugar reacts
• What is indicated by a brick red color in the Benedict's test?


  A positive result for reducing sugars
• What does a blue color indicate in the Benedict's test?


  No reducing sugar present
• What is the significance of the color change in the Benedict's test?


  It indicates the presence and concentration of reducing sugars
• How can the amount of reducing sugar in different solutions be compared?


  By observing the extent of the color change
• What is the purpose of using a colorimeter in the Benedict's test?


  To measure the absorbance of the remaining Benedict's reagent