Our Year 10 students have recently spent a term investigating some of the chemical and physical properties of alcohol. At Shearwater, Year 10 chemistry is about demystifying this substance that many teenagers are rightfully intrigued by.
We began with grapes! The students spent a morning feeling what it might have been like in a rural village at grape harvest time. How many of us have the opportunity to feel grapes between our toes? The strong inner structure of the grape demands a lot of force to crush it. How much sugar do you think is in a litre of grape juice and how can you tell? To find out the students measured the density of the juice with a hydrometer and were surprised to find that their juice contained as much as 250g of sugar per litre. That’s a lot of sugar!
They added the fungus that we know as yeast and waited patiently for the fermentation to happen. Those little dry granules of yeast really didn’t look like mushrooms but they certainly transformed the sugar into alcohol.
No one was particularly impressed with the wine but then we weren’t stopping there, that was just a means to obtain a much purer sample. After understanding that alcohol and water have different boiling points they were able to fractionally distil a much purer alcohol sample. How pure? Well, to determine this they went back to density – that had worked for sugar. This time though they first needed to make an instrument that could float in the alcohol and calibrate it with solutions of known percentages.
Glass blowing the hydrometer was a challenge but fun regardless and they soon recognised their samples were between 80% and 90%.
What to do with this precious material? Burn a little of course! It burns with a beautiful ghostly blue flame – hard to see in the light. It was way too precious to waste it all like this though the thought of that did appeal to some students. We used the remainder to extract the essence from calendula flowers, exploiting the solvent and preservative properties of the material we were now calling ethanol, to make a tincture.
A project was beginning to take shape. What else do plants have to offer besides sugars? A walk around the farm took us to the herb and fragrance gardens and we came back with lavender, lemon myrtle and tea tree.
Using a steam distillation method we were now able to extract fragrant essential oils and hydrosols from the plants that might be useful in making a product.
Using some of the remaining ethanol and butyric acid (found in breast milk, parmesan cheese, body odour and vomit) we synthetically produced a chemical that smells like pineapple but in a ‘fake pineapple lolly kind of way’, according to one student. This really brought home why those little bottles of essential oils cost so much – ‘so many leaves distilled and so few drops of oil gained’ according to another. It also reinforced why cheap food and cosmetics used artificial flavours and fragrances. It was so easy and cheap to make so much.
After purifying some bees wax and learning about emulsions, we combined a high quality carrier oil with our wax, hydrosol, essential oils and calendula tincture to make a hand cream of the finest quality ingredients.
As for me, I love teaching this unit. It’s fun and it really looks like you imagine chemistry to look – lots of glass tubes with exotic liquids dripping from them. The students thought so too. We are slowly perfecting the hand cream, perhaps you’ll be the lucky recipient of a bottle sometime.
Gerard Braithwaite
Science Teacher