2.1.2 q - CHEMICAL TESTS

q) Describe the Benedict’s test for reducing sugars.

• Add Benedict’s reagent to sample

• Benedict’s solution is blue

• Heat to 80’C using a water bath

• If reducing sugar is present, blue to brick red

q) Describe the Benedict’s test for non-reducing sugars.

• Add Benedict’s reagent to sample to confirm reducing sugars is not present

• Solution stayed orange

• Add dilute hydrochloric acid to another sample and heat solution in a water bath

• Neutralise the acidic solution with sodium hydroxide

• Add Benedict’s reagent to the solution

• Heat to 80’C with a water bath

• If reducing sugar is present - blue to brick red

q) Describe the iodine test for starch.

• Add iodine to sample

• If iodine is present - orange-brown to blue-black

q) Describe the emulsion test for lipids.

• Add ethanol to sample and shake

• Add sample-ethanol mix to water

• If lipid is present - solution will go from colourless to cloudy white emulsion

q) Define the term ‘qualitative test’.

Collecting data that cannot be expressed as a numerical value

Define the term ‘quantitative test’.

Collecting data that can that be expressed as a numerical value

Define the term ‘semi-quantitative’.

There is an indication of quantity, but it is not linked to a numerical value.

q) Explain how the Benedict’s test for reducing sugars can act as semi-quantitative test.

Because the solution can turn a different colour depending on the concentration of the glucose.

The colour could range from green, yellow, orange and brick red depending on the concentration.

q) List 5 examples of reducing sugars.

• glucose

• galactose

• fructose

• maltose

• lactose

q) State one example of a non-reducing sugar.

Sucrose