How Calcium Turns Seaweed Extract into Gel

In the picture

1. 1The runny liquid: without calcium, the seaweed extract solution pours out freely.
2. 2A long alginate chain molecule: on its own, it slides past the other chains.
3. 3A calcium ion wedged between two chains, clamping them together like an egg in an egg box.
4. 4The gel: the clamped chains form a network that holds the water in, so it does not pour.

Examples

• Popping boba in bubble tea: drops of juice mixed with alginate turn firm when they fall into a calcium bath.
• The soft paste a dentist uses to make a mould of your teeth sets because of alginate.

Quiz: How Calcium Turns Seaweed Extract into Gel (Age 14)

1. 1

   Before calcium is added, why does a seaweed extract solution pour so easily?

   • The alginate has not dissolved in the water yet
   • Its long chain molecules can slide past one another
   • Its chains are already linked, but too loosely to hold the water
2. 2

   What do calcium ions do when they are added to an alginate solution?

   • They join chains end to end, making each one much longer
   • They make the chains curl up into tight little balls
   • They clamp pairs of chains together, building a network
3. 3

   Why does an alginate gel hold its shape instead of pouring like the runny extract?

   • The network of clamped chains traps the water inside it
   • The calcium reacts with the water and turns it into a solid
   • The water gets squeezed out, leaving a solid made only of chains

The answers, each with its explanation, are in the app. This lesson has left the free week, so its quiz is part of the subscription.