Seaweed spheres

The borax/PVA slime experiment is a lot of fun, but a demonstration of the cross-linking in sodium alginate shows students the creation and destruction of gels through the exchange of ions of different charge.

If using food-grade ingredients outside of the lab, the products can be eaten!

I normally show this demonstration to students towards the end of a structure and bonding course. The alginate displays properties both of ionic and of covalent materials and students can see how changing the charge on an ion can have an impact on structure.

With an accompanying video, Declan Fleming demonstrates how to prepare and create seaweed spheres, and suggests additional activities which could be incorporated.