Whether you鈥檙e buying ingredients for an at home 鈥淐oke and Mentos鈥� demonstration, asking a flight attendant for a beverage, or just trying to pour a can of soda into a glass before hockey comes back on, you may have noticed something: Diet sugar-free sodas fizz more than regular sugar-rich sodas when opened.
The degree of carbonation or 鈥渇izziness鈥� of a soda is partly a function of how easily carbon dioxide bubbles can form in the sugary flavour water we call pop. When it鈥檚 easier for bubbles to form, you get more of them and therefore an increased 鈥渇izziness鈥�.
When a liquid has a high surface tension, it means that the bonds between the liquid鈥檚 molecules are very strong. Surface tension is why some spiders can walk on water鈥攖he spider鈥檚 weight isn鈥檛 enough to break apart the water molecules! In a substance with high surface tension, bubbles will not form very easily.
Surfactants are chemicals that decrease the surface tension of a liquid. They will therefore make it a bit easier for bubbles to form. Regarding Diet Coke, aspartame, and potassium benzoate (a preservative) ! Caffeine as well, but it has much less of an effect due to its low concentration.
Bubbles of gas will struggle to form in very viscous liquids, like maple syrup or waffle batter. Diet soda actually has a slightly higher viscosity than sugary soda, which slightly diminishes its fizzing potential. However, a slightly higher viscosity means that when bubbles do form, they鈥檙e a bit more stable. This why Diet Coke not only fizzes more than classic Coke, but the foam also lasts longer!
