As I write this month’s Exhibition chemistry from the depths of a Covid-19 lockdown, I’m getting very used to the inside of my own flat. However, that doesn’t mean there aren’t plenty of interesting chemical phenomena worthy of exploration using only items around the kitchen – so many in fact that I decided to narrow it down and make use of the fruit we’re all hopefully eating to keep healthy. I have a good stock of citrus fruits and want to show a few little tricks you can do besides just turning them into clocks.
If you were to freshly peel a citrus fruit such as an orange, grapefruit, lemon or lime, and you squeeze the peel over a flame… it will react! Most of the peel is made up of oil that contains a chemical called D-limonene and it’s very flammable. When it comes into contact with the flame, the oil ignites!
Demo 2: Balloon burster
- Orange
- Knife
- Candle
- Inflated balloon
Following the same procedure as above, cut a piece of orange peel and heat briefly over a candle flame to warm the oil sacs. This time, rather than squeezing the contents at a candle flame, try spraying the ejected oils at a well-inflated balloon or water balloon which, if taut enough, will pop.
This demonstration shows how compounds with similar intermolecular forces are miscible. The balloon is made of latex, which is a polymer of isoprene, the base unit from which all terpenes are built. The terpene oils from the citrus peel therefore show similar intermolecular forces (in this case London dispersion forces) – so the oil can dissolve into the latex and disrupt the forces between polymer chains, causing the balloon’s structure to weaken. This is not a problem for water which, being dominated by hydrogen bonding interactions, does not degrade the latex.
Once you return to school, you can show some other dissolving polymer effects. While it can take a few goes with orange oil to burst a balloon, the far more aggressive cyclohexane produces instantaneous and dramatic results.
Once you return to school, you can show some other dissolving polymer effects (rsc.li/2yybbeC). While it can take a few goes with orange oil to burst a balloon, the far more aggressive cyclohexane produces instantaneous and dramatic results.
These demonstrations are based on a wider lab exploration of volatile fragrance molecules from Science in School. A microscale distillation set-up can allow students to extract a range of terpenes quickly and easily from plant matter, test for unsaturation, and assess the product’s purity with thin layer chromatography.
For more information on terpenes, use James Kennedy’s fantastic infographic, which illustrates the wide range of places in which they appear.
These demonstrations are based on a wider lab exploration of volatile fragrance molecules from Science in school (bit.ly/3grE6ly). A microscale distillation set-up can allow students to extract a range of terpenes quickly and easily from plant matter, test for unsaturation, and assess the product’s purity with thin layer chromatography.
For more information on terpenes, use James Kennedy’s fantastic infographic (bit.ly/2TBS5eU), which illustrates the wide range of places in which they appear.
Demo 1: Flame thrower
Cut off a piece of peel from an orange (3–5 cm in length and 2–3 cm wide is ideal), cutting as deep as possible without removing any juicy flesh. Heat the peel over a lit candle for a few seconds and then hold the warm peel, pointing the outer side of the peel towards the side of the flame, and firmly squeeze the top and bottom together to fold it in half. A burst of flame will shoot 5–10 cm from the candle and a puff of thick black soot will be released.
The peel consists of two layers: the colourless, spongy inner albedo layer and the outer, coloured flavedo layer, which is rich in oil sacs containing peel oils. A major component of this surprisingly flammable oil is D-limonene. The unsaturated monoterpene is produced from two isoprene units – the building blocks of a range of chemicals familiar to students including menthol and R-carvone (mint and spearmint), oestrogen and testosterone, and the carotenoids which give many plants their yellow or orange colouration.
The flavedo of an orange is rich in carotenoids (eg violaxanthin) which, with their extended delocalised pi-system, are able to absorb blue light and appear orange. A lemon’s paler yellow flavedo, meanwhile, has a lower concentration of carotenoids. In this mixture there is also a much higher proportion of phytoene which, with less extensive delocalisation than other carotenoids, absorbs in the UV rather than the visible part of the EM spectrum, appearing colourless.
These heavily unsaturated compounds burn with a characteristically smoky flame – the explanation is explored in the article Clearing the air around smoke formation.
These heavily unsaturated compounds burn with a characteristically smoky flame – the explanation is explored in the article, ‘Clearing the air around smoke formation’ (rsc.li/2M1DFjW).
Once you return to school, you can show the smoky and clean-burning flames of alkenes and alkanes with the cracking and hydrogenation demonstrations.
Once you return to school, you can show the smoky and clean-burning flames of alkenes and alkanes with the cracking and hydrogenation demonstrations (rsc.li/3d6kDox and rsc.li/2ZGikEO).
Portal 2 Combustible Lemon
FAQ
Are lemons combustible?
What happens when lemon is heated?
Why lemon should not be heated?
Why must you not squeeze lemons on hot food?
What foods are flammable?
Be Careful of the Most Common Flammable Items in Your Kitchen. Flour, sugar, oils, cooking alcohols, milk, and creamer all serve as base ingredients for several different dishes. Each ingredient is flammable in a different way and needs to be handled properly. 1878. Similar
Does Real Lemon have the same effect as a natural Lemon?
Real lemon is a type of acidic lime, derived from the original lemon. They have distinct characteristics and are used for different purposes. Therefore, the effect of each may vary depending on use.
Can you eat lemons whole?
Unlike other fruits, lemons aren’t typically eaten whole. Instead, you can use them to add flavor to water or foods, such as chicken, fish, pasta, or vegetables. You can also use lemons to make fresh lemon juice — just keep in mind that it takes about six lemons to get 1 cup of lemon juice.
Is cinnamon flammable?
Cinnamon contains cinnamaldehyde and eugenol. Aside from giving cinnamon its unique flavor and odor, these compounds are also flammable. Much like flour, cinnamon can cause an explosion if too much of it gets into the air and ignites. Garlic contains a lot of oil, so it burns very quickly when exposed to heat or fire.