2.1.2d Testing for Glucose (PAG 9.3)

Question 1

What does the term qualitative test mean

Answer 1

Only gives us a positive or negative result to tell us whether a particular substance is present. It does not tell us how much of the substance is present (or at what concentration).

Question 2

What is the test for sugars (glucose and sucrose)

Answer 2

Benedict’s test

Question 3

Aim

Answer 3

To test qualitatively for the presence of glucose (a reducing sugar) and sucrose (a non-reducing sugar)

Question 4

Chemicals involved in the tests + hazard

Answer 4

• Benedicts reagent (low hazard but avoid contact w eyes)
• 2.0 mol dm^-3 hydrochloric acid (causes skin and eye irritation)
• Sodium hydrogen carbonate (low hazard)
• Samples (A-D)

Question 5

Equipment needed for the tests

Answer 5

• Benedicts reagent
• 2 dropping pipettes
• 8 boiling tubes
• 8 x 5cm^3 syringes
• Samples in beakers, labelled A, B, C
• Water bath set to 100dc
• 2.0 mol dm^-3 hydrochloric acid
• Sodium hydrogen carbonate
• Small spatula
• pH paper

Question 6

Health & safety of the tests

Answer 6

• Eye protection must be worn due to presence of boiling water & acid
• Benedicts reagent is low hazard but contact w eyes should be avoided
• Boiling water bath presents a scalding hazard
• 2.0 mol dm^-3 hydrochloric acid is an irritant

Question 7

What is method 1 of testing sugars

Answer 7

Testing for reducing sugars

Question 8

Method for testing reducing sugar (1)

Answer 8

1. Label 4 boiling tubes A-D & place 4cm^3 of the corresponding samples into each using a fresh syringe each time
2. Using dropping pipette, add 2cm^3 Benedicts reagent to each of 4 samples
3. Record observations of each sample immediately after adding Benedict’s reagent
4. Place all 4 boiling tubes into the water bath
   5.