Science Experiments From Home: Make Learning Fun With Invisible Ink
Kids love writing secret messages to each other and while we sell spy pens (in the pocket money section of our website), we think it's a whole lot more educational to make your own invisible ink using lemon juice. It's also a great way to introduce your children to some fun chemistry experimentation, whilst practising their handwriting at the same time. Who knew handwriting practice could be so much fun! And if you want to get cute, get them to practice their foreign language learning with invisible ink too. Or their multiplication tables, division, you name it, the options to turn learning into some good old fun are endless.
Here is the background science information you'll need to answer your children's questions.
Why does the lemon juice turn brown when its heated by the light bulb or flame?
Lemon juice contains compounds which have carbon atoms in them. These compounds are largely much colorless at room temperature. But heat can break down these compounds, releasing the carbon. If you think of coal and other carbon rich compounds such as soot, you’ll note they are a very dark, almost black colour, because the carbon is dark.
When the compounds in the lemon juice are broken down, the carbon comes in direct contact with the air, and a process called oxidation occurs. When this happens the lemon juice on the paper (or more precisely the carbon containing molecules of the lemon juice), turn a darker brown colour.
Cut An Apple & Demonstrate the Same Colour Change By Oxidating Carbon
You can see oxidation without needing to apply heat. Some fruits can turn brown from oxidation when they’re cut, it is very obvious in apples when you cut them. Once the surface of a cut apple is exposed to the atmosphere, it will turn a reddy brown colour. This is due to the carbon containing molecules in the apple juice being oxidised by the air.
What is Oxidation?
Oxidation happens when a compound gains electrons (negatively charged sub atomic particles), via the gain of oxygen or the loss of hydrogen. It’s an interesting and important chemical reaction.
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