## Wednesday, 15 July 2015

### Science experiment: Diffusion

In short, diffusion, involves molecules moving from higher concentration to lower concentration.  This movement is known as the concentration gradient.

This happens with liquids and in gases.  As gases are more difficult in an experiment to show children how diffusion works I will use this experiment which involves liquid, in this case water.

We will also experiment with temperatures in the experiment and talk about how temperature effects the rate of diffusion.

First the experiment...

Equipment needed:

• Hot water
• Cold Water
• 2 clear cups
• 2 pipettes
• 2 food colours  (I choose purple and blue)

STEP ONE

500ml of water to one large clear cup and 500ml of hot water to the other clear cup.

You will need a responsible adult present as you are dealing with hot water.

STEP TWO

Now get your pipettes.  Add 2ml of one colour to the centre of the top of your cold water.

The colder the water the better, so long as it is still in liquid state.

STEP THREE

Now add 2ml of the second colour in the centre of the top of the hot water.

 cold
 hot

Which diffuse quicker?

The hot water right?

As I said, in this experiment we will look at how temperatures effect the rate of diffusion.

The diffusion of food colouring in hot and cold water showed us clearly how temperature effects the rate of diffusion, with the process being much faster in hot water than in cold water.

This is because heat provides energy and the energy from the heat makes the molecules up and makes the move faster so the diffusion process works quicker.

The cold can take a lot longer however it will eventually completely diffusion into the water, which is of lower concentration (as it has no food colouring in to start with) until the whole cup is full of equal amount of concentration.

In Nature!

Diffusion is something that happens in the body, at the alveoli.  As we breath in air, the air that arrives has a higher concentration of oxygen than the air in the alveoli sacs.

This increase in concentration creates a concentration gradient for oxygen what causes the oxygen to diffuse through the thin walls of the alveoli and enter the blood in the capillaries that surround the alveoli, that's being pumped around the body by the heart.

Not all the oxygen goes through the wall, the oxygen in the alveoli and the oxygen through the wall is just balanced out: we do still breath a bit of oxygen out when we exhale.

At the same time the air arriving into the alveoli effects the concentration of the carbon dioxide, as when new air comes in the carbondioxide (CO2) in the alveoli decreases as air is low in CO2 concentration.

This causes the carbon dioxide in the blood to diffuse into the alveoli, which is why there is more carbon dioxide present when we breathe out.

This experiment helps us understand how and why the exchange of these gases happen and is one of the experiments I use to demonstrate to kids how this happens.