Carbohydrates - Disaccharides

Question 1

How are disaccharides formed

Answer 1

Formed by the condensation of two monosaccharides

Question 2

Maltose

Answer 2

Formed by the condensation of two glucose molecules

Question 3

Sucrose

Answer 3

Formed by condensation of alpha glucose and fructose molecule

Question 4

Lactose

Answer 4

Formed by condensation of alpha glucose molecule and galactose molecule

Question 5

Function of disaccharides

Answer 5

• sugar found in germinating seeds
• mammal milk sugar (lactose)
• sugar stored in sugar cane (sucrose)

Question 6

Test for reducing sugars

Answer 6

• 2cm3 of Benedict’s reagent
• heat in water bath
• blue to brick red

Question 7

How does the reducing sugar test work?

Answer 7

• all monosaccharides and some disaccharides are reducing sugars
• reducing sugar donates electrons to another chemical (Benedict’s reagent)
• Benedict’s reagent is an alkaline solution made up if copper (II) sulfate
• a carbon atom on sugar is bound to O and to an OH group
• reduces Cu2+ in the CuSo4 in Benedict’s reagent to Cu+
• causes colour change from blue to red as Cu+ PPTS out of solution.

Question 8

Test for non-reducing sugars

Answer 8

• need to hydrolyse it into its monosaccharides first
• use dilute hydrochloric acid to hydrolyse sugar
• neutralise using sodium hydrogen carbonate solution
• retest using Benedict’s reagent
• if non reducing sugar is present, it turns brick red.