Hum, another brain teaser for us to ponder over.
We’ve been making jelly with gran. You’ve been fascinated by the jelly cubes – look they have dissolved, how long will it take to set into a wibbly wobbly jelly and a host of other questions.
Well, let the investigations begin. Do they dissolve or do they melt, why does the jelly set, how long does it take?
Jelly answers seem just as elusive as the “Can giraffes swim” question. I’ve found loads of school lesson plans for making a jelly, but little to explain what is actually happening. So, I’ve taken a new approach. Firstly, to find out what the difference is between melting and dissolving, then apply this to the jelly example.
Melting and Dissolving
- When something melts the liquid is the same substance as the solid.
- Not all solids melt on heating (they may burn or decompose).
When something dissolves an additional substance is needed.
- Dissolving can involve chemical changes (for example, antacid tablets mixing with water or metal dissolving in acid).
- Dissolving results in a solution. The solution consists of a solute (substance being dissolved) and a solvent (the medium it is dissolved in) is called a “solvent”.
Melting and dissolving are not the same.
- In melting only one substance is involved and the liquid and solid are the same material. Heat is needed for melting to occur.
- Dissolving involves two materials; the resulting solution is a mixture of both. The dissolved substance is still present in the solution even though it can’t always be seen.
A Note to You and Me
So, we’ve decided that jelly cubes probably dissolve when added to hot water. Jelly cubes are definitely not ice cubes hence, we think there are at least two substances involved. The “jelly cube” solution is a mixture of whatever jelly cubes are made from and water.
Yes Kam, I was waiting for it, what are jelly cubes made from? Hang on in there, we’ll get work that out next! X