5 Minute STEM Activity 16 - Scared of soap

This is a great little activity which takes seconds and, like the Gluten activity earlier, it helps children understand what it is that really makes up the foods they eat. We are going to scare colour into running away...

Scaring away the colour in milk - with soap

EQUIPMENT:
A breakfast bowl
About 2oz milk - enough to cover the bottom of the bowl. Any milk should work, although I've not tried them all!
A tiny amount of food colouring
2 drops of washing up liquid

Instructions:

1. Put the milk into the bowl. You just need enough to cover the bottom, not very much.

2. Add a couple of drops of liquid food colouring, or if you have gel colours, get a tiny blob on a teaspoon handle and dab it in the milk or draw a shape. Don't 'mix' the milk and the colour.

3. Very carefully drop 1 drop of washing up liquid into the milk. The centre is a good place. If you don't trust yourself to be careful, use an old medicine syringe (throw it away afterwards) or pipette for your drop. Never use anything you use for insect or fishkeeping, as washing up liquid is very dangerous to them.

4. The colour should immediately run away from the washing up liquid - it's a dramatic effect.

If you have a lot of food colouring in one place, you can try another drop. Why do you think the food colouring ran away?

It's a trick. The food colouring is just there so that you can see everything properly. In fact it is the fat in the milk which runs away, causing ripples in the water and dragging some of the food colouring with it.

Soap has two types of special molecules called hydrophobic and hydrophilic - the hydrophobic particles hate water. They grab onto the dirt and grease to try and get away from it. This is why your plates become shiny and clean when you rub soapy water onto them and then rinse it away. The hydrophilic particles like water, they mix with it and make the bubbles.

You can find all of the 5 Minute STEM Activities here...  None cost more than pennies or need anything you won't find in most homes (save your cereal boxes).

Hands on STEM is learning that is fun!