Australian Science Illustrated – Issue 51 2017

scienceillustrated.com.au | 79

Salt water reveals

colouring agents

Are the colouring agents in your lollies composite products? Thanks to a little

salt water, this simple experiment can reveal the true make-up of the colours.

W

hen chemists to try to find out

whether a substance is a

composite, they use a method known as

chromatography. The simple method

distinguishes between different chemicals.

To carry out chromatography, you

must have a test object and two phases: a

stationary phase and a mobile phase,

which can pass through the stationary

phase. In this experiment, the salt water

is the mobile phase. The filter is in the

stationary phase.

The salt water contains ions with

major positive and negative charges from

the dissolved salt, making charged

colours bind to the salt water and follow

it up through the coffee filter. Colours

with little or no charge do not bind to the

salt water, and they are left at the bottom

of the coffee filter.

Charge pulls up colours

Blue colour

The blue colour is

charged and binds to

the sodium and

chlorine ions of the

salt. The colour follows

the water up the filter.

Green colour

Green is a mixture of

yellow and blue. The

charged blue colour

moves upwards, but

the neutral yellow

colour does not.

Yellow colour

When the colour is

not charged (yellow

in this experiment),

it will not bind to

the salt water,

remaining at the

bottom.

SALT WATER

COFFEE FILTER

Only some of the colours of your
sweets bind to salt water, passing
up through the coffee filter.