Carbohydrates - monosaccharides and disaccharides Flashcards
What three elements are found in monosaccharide?
carbon, hydrogen and oxygen
Name the two isomers of glucose.
alpha glucose and beta glucose
Name two monosaccharides other than glucose
fructose and galactose
Describe the test for reducing sugars, including positive and negative results.
Add Benedict’s reagent (blue) and heat.
Negative result = stays blue. Positive result = coloured precipitate formed, red, orange, yellow or green.
Describe how you can find out how much reducing sugar is present (quantitative).
Dry and weigh the precipitate, use a colourimeter.
What are the advantages of using a colourimeter to measuring concentration of reducing sugar?
Standardised method, not subjective, quantitative.
What is a disaccharide and describe how one is formed?
A disaccharide is formed when two monosaccharides are joined together in a condensation reaction.
Name the chemical bond that is present in a disaccharide.
Glycosidic bond
Which monosaccharides are found in maltose?
alpha glucose
Write a word equation for the formation of maltose, sucrose and lactose.
alpha glucose + alpha glucose => maltose + water. glucose + fructose => sucrose + water glucose + galactose => lactose + water
Name the two disaccharides that are reducing sugars.
Maltose and lactose
Describe the test for non-reducing sugars.
Add Benedict’s reagent (blue) and heat. Negative result = stays blue. Get a new sample and add dilute HCl and boil, then neutralise it with sodium hydrogen carbonate. Then add Benedict’s reagent and heat. Negative result = stays blue. Positive result = coloured precipitate formed, red, orange, yellow or green.
