Some tips for Science Sleuths:

Chemical Change.

How can you tell if a chemical change has taken place?

Scientifically if you have produced a new substance then you have witnessed a chemical change, but unless you know what to look for you can be unsure. Chemical changes can happen right before your eyes so Science Sleuths need to hone up their observation skills. Sometimes they might have to delve further and look at the properties and behavior of the new substance, and compare these to the old. That’s why a cunning Science Sleuth will often write down as much information as they can about their starting products before they begin to experiment (easier to compare that way!).

There are many ‘clues’ that young Science Sleuths can be aware of to help them decide whether or not they have found a chemical change:

Colour change: often an easy-to-recognize clue.

Gas bubbles escaping: if gas bubbles have escaped, then that means what you have left is different to what you started with. Remember gases are substances too, if they escape into the air then some of your starting products are no longer there!

Change in property: if your starting substance was attracted to a magnet, but your new product is not, chances are there has been a chemical change. Other properties to be aware of are:

Do your substances burn?

Do they react with acid (eg vinegar or lemon juice)?

Are they a solid at room temperature, and if so are they easily molded or are they brittle, etc? You wouldn’t use this observation on its own; it is not enough information to be sure there has been a chemical change. If your new substance is different at room temperature, chances are you have something new, but be careful here because often mixtures can have different properties, but they are not chemically different (that is, all of the substances you started with are still there in the same form that they were at the start, just mixed). I didn’t say this scientific detective work would be easy! That’s why the next point needs to be considered carefully:

Can you easily change your substance back to what you started with? This is the one I like because you can have fun testing this out. Here is a good example: if you heat butter just a little bit (like leaving it out in the sun, or heating gently just until it melts), can you change it back to a solid that is the same colour and taste as before? Try it. OK. Now heat the butter in a pan until it changes colour: Can you change it back to a solid that is the same colour and taste as before? Try it. Perhaps try what you did the first time. Did it work? Have you uncovered a chemical change?

Another good example for an adventurous Science Sleuth is using jelly. Mix it with cold water. What do you end up with? Can you get back the jelly crystals just like they were at the start? How? Try it.

Now mix them with boiling hot water. What do you end up with? Now can you get them back?

If you would like to email me your thoughts on any of these important matters I would be happy to comment on your findings.

Signing off now,

Your friendly science educator,

Jenny Arnold

Dept Science & Mathematics Education
The University of Melbourne
arnoldj@unimelb.edu.au