Water is the most abundant molecule in cells, organism, and on earth and it is so vital to life due to a combination of its unique chemical and physical properties.
Let’s first take a closer look at the structure of this essential molecule; water is polar (meaning that it has small charges on the individual atoms in the molecule which let it bond to other water molecules). This is so important and influences all other properties of water. Because water is polar, it can interact with other substances (such as salt) to dissolve them. In our bodies, all the chemicals are dissolved in water in our cells (in the form of the cytoplasm): water allows us to exist at a cellular level.
The solid form of water (ice) demonstrates another cool property of water as ice is actually less dense than its liquid form. We probably all take this surprising physical property of water for granted, however, for all other substances, the opposite is true. Ice is less dense than water because when the liquid cools down and molecules lose energy, more hydrogen bonds form between the molecules- forcing the molecules into a more spread out lattice to accommodate for the maximum amount of hydrogen bonds.
This unique physical property ensures that, even when its really cold, bodies of water such as lakes and oceans freeze from top-down – insulating the water below the surface and protecting aquatic life. This special property of water might have prevent organisms from going extinct in the past.
Water is so important to life that it is no wonder that we are almost constantly told to remain hydrated, especially in the summer. Naturally, in order to transport water, the majority of us use plastic water bottles: they’re convenient, lightweight, and cheap. But their hidden cost comes in the form of the damage it does to our health and the health of the planet.
The fact that plastic poses a risk to the environment probably doesn’t come as a shock to you. Despite this, you would probably still be forced to use plastic bottles since there are virtually no other cheap, lightweight alternatives that can even hold a candle to plastic. Until now…
Introducing Ooho! A water bottle that is completely edible and 100% biodegradable. Developed by Skipping Rocks Lab and inspired by the natural membranes found in eggshells, these orbs of water are encased in a calcium alginate gel layer and formed through a fascinating process known as spherification which was developed, not by chemists, but by chefs.
The process of spherification was pioneered in the 1950s by Unilever and it involves the reaction of two common chemicals which can form a tough membrane on the outside of the water- essentially, the water became its own water bottle through polymerisation. The first ingredient of the edible ‘water bottle’ is Sodium Alginate, usually derived from seaweed. This is a long-chain carbohydrate that is soluble in water. In its original plant, it is used to store sugars created by photosynthesis. When Sodium Alginate is dissolved in water, these long-chain carbohydrates float around on their own but they don’t connect to each other. That’s because poking out from these long chains is a branch of carbon and oxygen atoms, which chemists call an anionic group which has a slight negative charge. The sodium ions are attracted to this, because they have a positive charge. But sodium is monovalent, meaning that it wants to bond to just one of these carbon and oxygen branches at a time.
However, if you add calcium ions to the solution, the structure changes. Calcium ions have two positive charges, so they want to bond onto two of these branches at a time, meaning that it can connect two alginate molecules together. So the calcium ions replace the sodium and create cross-linkages between the long-chain carbohydrates. When enough of these chains are connected together, this 3D matrix of connected alginate chains forms a semi-solid impermeable membrane that the water can’t pass through -creating a sphere that surrounds the water. The fully formed water sphere is made from nothing but water and the two chemicals!
As part of the session, we experimented with sodium alginate and calcium lactate to design our own edible ‘water bottles’. We first dissolved one gram of sodium alginate powder into 250 ml of water to create sodium alginate solution, Then we dissolved five grams of calcium lactate powder into 1250 ml of water to create a calcium lactate bath. We then gently set a tablespoon of the sodium alginate solution into the calcium lactate bath- allowing the spoon to become completely immersed before tipping it over to pour out the sodium alginate solution.
The main difficulty was estimating when to remove the water orbs from the calcium lactate bath; we came to the conclusion that 20 minutes is the minimum amount of time needed for the membrane to solidify properly whereas leaving the ‘water bottles’ submerged for an hour ensured that the membrane remained flexible but strong.
Avenues for further investigation would be to freeze the sodium alginate into spheres and then submerge the solid spheres into the calcium lactate bath to produce ‘water bottles’ with a more defined shape and to experiment with calcium chloride which is said to produce a stronger membrane. Overall, however, I feel the experiment was fairly successful and we were able to sample numerous ‘water bottles’!
This technique is causing a bit of a stir in manufacturing circles as it could provide a waste-free way to contain and transport water as the membrane is both edible and biodegradable. It is still a long way from replacing the water bottle on store shelves, however, as the gel membrane breaks down over time and isn’t as tough as plastic.
This blog post is based on the course content I created for a series of sessions on the biochemistry of water as part of the Exploring Everyday (Bio)Chemistry Society which I run at The Tiffin Girls’ School. The sessions focus on connecting chemistry with everyday products and phenomena to encourage KS3 engagement with science and they have been a great success so far. More blog posts based on this society can be found here.
Curiosity Killed The Cation 