Carbohydrates - Disaccharides and Polysaccharides

Question 1

What makes maltose, sucrose and lactose

Answer 1

Maltose - glucose and glucose

Sucrose - glucose and fructose

Lactose - glucose and galactose

Question 2

What reactions joins monosaccharides. What’s removed

Answer 2

Condensation

Water molecule

Question 3

What’s the bond formed between two monosaccharides

Answer 3

Glycosidic

Question 4

What happens when water is added to a disaccharide under suitable conditions

Answer 4

If breaks the glycosidic bond releasing the constituent monosaccharides. This is hydrolysis

Question 5

What’s the test for non reducing sugars

Answer 5

Benedicts rest

Heat with benedict’s solution and get no change ( carry out reducing sugar test)

Take a fresh sample and heat with dilute hydrochloric acid- place test tube in water bath for 5 mins

then neutralise the acid with sodium hydrogen carbonate

Retest soliton by heating 2cm in water bath for 5 mins

Observe colour change (brick red)

Remember that is test can also be semi quantitative if you link colour to amount of
glucose or measure absorbance using a calorimeter

Question 6

Polysaccharides are very large molecules and insoluble. Why’s this good

Answer 6

Makes them suitable for storage

Question 7

What’s the starch test

Answer 7

Add 2 Cm of sample being tested in test tube

Add 2 drops of iodine solution and shake

If starch is presence, it will turn blue / black