I’m running an outreach activity and we’ll be making alginate worms. I was testing my sodium alginate solutions yesterday as they tend to go off a bit. Usually this is demonstrated by no longer forming beautiful worms or spheres on addition to calcium chloride solution but rather forming slime. I suspect the polymer chains are being clipped. I add food dye as well – coloured worms are more fun.
One bottle yesterday was colourless and was a 2% solution of sodium alginate (food grade) that had been prepared a few months ago and was dyed with indigo carmine food dye (powdered). It had been stored in the dark (filing cabinet, my office) at 22 deg C for 4 months. On opening it stank of rotten eggs so I quickly recapped the bottle and turfed it in the sink for cleaning. When I came back to it 30 mins later, it was a blue solution and still stinky!
The other solutions were the appropriate colour and all formed decent worms.
I thought it was quite a nice wee chemical puzzle – anyone want to take a guess at what was going on? I have a working hypothesis which I’ll share later.