My daughter is a fan of seaweed, which comes in an excess of packaging that includes packets of silica gel stamped with “Do Not Eat.” I wondered what the silica did and how hazardous it was. Naturally, I decided to investigate.
Silica is another name for silicon dioxide, a molecule composed of one silicon and two oxygen atoms, among the most abundant elements in the Earth’s crust. Sand is mostly silicon dioxide and quartz is a common crystal form of it. Glass is also made with it.
Silica gel packets in the seaweed contain hard little beads. They are made through a process involving sodium silicate and an acid patented by chemistry professor, Walter Patrick, of Johns Hopkins University in 1919. The mixture forms a gel that is then dried out. It is technically a xerogel but gets shortened to gel even though it is hard, just to confuse people.
Silica gel is a desiccant that can hold 30 to 40% of its weight in water. Water molecules stick to its surface, which is called adsorption. The similar-sounding phenomenon of absorption, involves the material being chemically incorporated into the material itself.
Each silica bead has many tiny interconnected pores, resulting in high surface area. The tiny pores also hang on to moisture through capillary condensation, which means that, even when saturated with moisture, the beads seem dry. Fancier types of silica gel contain other chemicals that change colour when they are saturated with moisture.
The silica gels work best when in a sealed container, and the beads themselves are in a breathable bag. But, in the case of the seaweed silica packet, the wrapping seemed to be plastic, which didn't seem right, so I put it in water. The water and it did not seem to pass through to the silica. This makes me wonder how useful it really was.
I then repackaged seaweed into two resealable bags and had one with the silica gel and one without. A day later, they both seemed fine, so that did not really tell me much. The experimental design needs work and time, if anyone would like to pursue that.
If you totally immerse silica beads in water, they make a popping sound and some of them break apart. I haven’t found a good explanation for this. I am imagining that perhaps the water molecules filling up the pores might somehow result in uneven pressures inside the bead, which with all the pores might be vulnerable to breaking.
Although silica itself is non-toxic, you should not eat those packets for at least five reasons:
- It might cause discomfort if you ate it because it might locally absorb more moisture than is likely good for you.
- The package might get stuck somewhere inside your body.
- If the beads break apart inside you, the pieces might not feel good.
- If you use the kind that change colour, those chemicals could be toxic.
- It could have adsorbed something toxic; you don't know where it's been.
If you still ate it and you don't feel well, here's some first aid advice.
If you have some silica gel, you can find lots of uses for it. Some people use left over packets to reduce moisture in their cars, for example.