Tuesday, 26 March 2013

Hot Chocolate for science: Insulators

This has to be up there on my tastiest experiments! It involves chocolate and lots of science so is pretty cool or in Chiara's words (when she was age 10) -  this is the best science lesson ever!
 

What you will need for this experiment is:
  • 2 identical cups
  • Hot chocolate drink powder
  • Marshmallows
  • A thermometer
  • boiling water
  • A science journal or some other piece of  paper
  • Pens or pencils
  • A ruler

STEP ONE
 
Make a table that looks a bit like this...
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
(If you click on any word on the above table it will lead you to a free PDf file to make it easy for you to print out)
 
or this...

 
This is Honi's table I helped with the tiny writing but she done the rest.

Now you can set up the experiment... 

STEP TWO

Decide how you are going to make this a fair test!
We must only change one thing and in this experiment it is marshmallows! Yum!  This does mean it is important to make sure both your mugs are identical, both mugs have exactly the same measured out amount of Chocolate drinking powder (in our case 25ml in each cup).  And when you add the water it is from a freshly boiled kettle each time.
 
If you have 2 thermometers you can do this experiment simultaneously but we didn't so we done them separately and in a way it made it even more exciting for the girls.  They talked so much about what they were finding out and what they were discovering.  It really is a fun experiment. 
 
STEP THREE

Ask the children about what they think will happen in this experiment. 
 
  • Will there be any difference between the mug with marshmallows and the mug without? 
  • What sort of difference? 

Remember they don't need to be right, it's a hypothesis.  I love when they hypothesise things that seem to us a little ridiculous because it means they are thinking for themselves, they are also thinking outside the box and one day that thinking may be how they discover something new!
 
STEP FOUR
 
Prepare both identical mugs  with 25ml of your Chocolate drinking powder. 

STEP FIVE

Boil your water up and as soon as the kettle has finished boiling, pour the hot water into the first cup with the thermometer in the cup and put the kettle aside away from the children. 

Wait for the temperature on the thermometer to settle and when it has that is your starting point, ours was around the 90 degree C mark.



Write this down under the 0 minutes time row under the without marshmallows column.  This is your starting point 

STEP SIX

Wait 2 minutes.  Check the temperature again and write in under 2 and then wait another 2 minutes and write the temperature after 4 minutes and keep doing this until you've completed 6, 8 and 10.

STEP SEVEN

Now you will need to do the same again but this time, after the just boiled water has been added, you need to put a layer of marshmallows on top. 

Again wait until the temperature of the thermometer has settled and this will be your starting point for the hot chocolate with marshmallows test so write this under the with Marshmallows column and the 0 time row.  Again every 2 minutes write down the temperature.

You are finished and your table should look something like this...




I found my girls, without prompting, were talking about:

  • How quickly the hot chocolate was cooling down
  • What point it cooled down the quickest.
  • Were comparing how the quickly the temperature changed with marshmallows to without. 
  • Discussed why this might be.
Taking this experiment further...

You can make graphs using the computer or by hand which is maths and will help to visualise the results too.

So which did cool the quickest?

The one without marshmallows. 

Why?  
 
What happened?

The mug with marshmallows cooled slower because the marshmallows acted as an insulator stopping the heat from the hot chocolate reaching the air quicker.  Heat will always flow from warmer to cooler.  There are three ways in which is does this:

  1. Conduction - Which is the way heat moves through materials.  It is the way a mug and the thermometer heats up when you add the hot water in this experiment.
  2. Radiation - this travels in a straight line and is the type of heat that comes to earth from the sun.  It is also heat that warms your hand when you put it near the mug.
  3. Convection - This is the movement of heat through liquids and gases.  Warmer fluids move upwards and this heats the air at the top of the hot chocolate and because hot air rises it is then replaced by cooler air.  what happens  when we added the marshmallows is it reduced the air movement over the hot chocolate slowing down the process of convection, the transfer of heat.  You would have noticed that there was more steam coming from the hot chocolate without marshmallows than the one with.
Another place you will find insulation:

In houses you will find insulation, it will help a house stay warmer through the colder months and cooler through the heat of summer. 
 
House insulation is made up of foam in a similar way to the marshmallows.  This is because they are filled with pockets of air; air doesn't conduct heat very well and the air trapped in the pockets of the foam are trapped, they can not flow which retains the heat of a house on a cold day or, on a hot day, keeps the heat from outside getting into the house.

Thermos flasks work in a different way.  In a thermos flask there are two chambers, it reduces airflow but instead of using pockets of air, it removes air from the equation.  You pour your hot chocolate into a thermos flask and it fills a central chamber.  There is a vacuum layer between the inside chamber and the outside chamber this means there is no air that the heat can use to transfer the heat from inside the flask to outside of the flask therefore keeping you hot chocolate toasty warm. 

So the Vacuum is a more effective barrier.  So now the question is how do you like your hot chocolate best?  With or without marshmallows?

What else we can learn from this
 
  • We learnt how to make a test fair.  To make a test fair you must only change one factor.  You can use this to discuss why.
  • Collecting Data - yes a bit of maths!
  • Making graphs - yes some more maths

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