What You Need to Know
When a sodium alginate solution contacts a calcium chloride bath, divalent Ca²⁺ ions replace the sodium ions in the alginate chains, forming a three‑dimensional cross‑linked network that solidifies into a thin shell. The reaction is rapid, completing within seconds, and the core remains fluid while the shell hardens. The process is governed by the concentrations of alginate and calcium, temperature, and exposure time.
The Science
Primary Reaction
Cross‑linking of alginate chains by Ca²⁺ ions to form a gel shell